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llvm/lib/Analysis/ValueTracking.cpp
Sanjoy Das 9b2526d03d [ValueTracking] Don't do an unchecked shift in ComputeNumSignBits 
Summary:
Previously we used to return a bogus result, 0, for IR like `ashr %val,
-1`.

I've also added an assert checking that `ComputeNumSignBits` at least
returns 1.  That assert found an already checked in test case where we
were returning a bad result for `ashr %val, -1`.

Fixes PR32045.

Reviewers: spatel, majnemer

Reviewed By: spatel, majnemer

Subscribers: efriedma, mcrosier, llvm-commits

Differential Revision: https://reviews.llvm.org/D30311

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296273 91177308-0d34-0410-b5e6-96231b3b80d8
2017-02-25 20:30:45 +00:00

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//===- ValueTracking.cpp - Walk computations to compute properties --------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains routines that help analyze properties that chains of
// computations have.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/OptimizationDiagnosticInfo.h"
#include "llvm/Analysis/VectorUtils.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalAlias.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Statepoint.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include <algorithm>
#include <array>
#include <cstring>
using namespace llvm;
using namespace llvm::PatternMatch;
const unsigned MaxDepth = 6;
// Controls the number of uses of the value searched for possible
// dominating comparisons.
static cl::opt<unsigned> DomConditionsMaxUses("dom-conditions-max-uses",
cl::Hidden, cl::init(20));
// This optimization is known to cause performance regressions is some cases,
// keep it under a temporary flag for now.
static cl::opt<bool>
DontImproveNonNegativePhiBits("dont-improve-non-negative-phi-bits",
cl::Hidden, cl::init(true));
/// Returns the bitwidth of the given scalar or pointer type (if unknown returns
/// 0). For vector types, returns the element type's bitwidth.
static unsigned getBitWidth(Type *Ty, const DataLayout &DL) {
if (unsigned BitWidth = Ty->getScalarSizeInBits())
return BitWidth;
return DL.getPointerTypeSizeInBits(Ty);
}
namespace {
// Simplifying using an assume can only be done in a particular control-flow
// context (the context instruction provides that context). If an assume and
// the context instruction are not in the same block then the DT helps in
// figuring out if we can use it.
struct Query {
const DataLayout &DL;
AssumptionCache *AC;
const Instruction *CxtI;
const DominatorTree *DT;
// Unlike the other analyses, this may be a nullptr because not all clients
// provide it currently.
OptimizationRemarkEmitter *ORE;
/// Set of assumptions that should be excluded from further queries.
/// This is because of the potential for mutual recursion to cause
/// computeKnownBits to repeatedly visit the same assume intrinsic. The
/// classic case of this is assume(x = y), which will attempt to determine
/// bits in x from bits in y, which will attempt to determine bits in y from
/// bits in x, etc. Regarding the mutual recursion, computeKnownBits can call
/// isKnownNonZero, which calls computeKnownBits and ComputeSignBit and
/// isKnownToBeAPowerOfTwo (all of which can call computeKnownBits), and so
/// on.
std::array<const Value *, MaxDepth> Excluded;
unsigned NumExcluded;
Query(const DataLayout &DL, AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT, OptimizationRemarkEmitter *ORE = nullptr)
: DL(DL), AC(AC), CxtI(CxtI), DT(DT), ORE(ORE), NumExcluded(0) {}
Query(const Query &Q, const Value *NewExcl)
: DL(Q.DL), AC(Q.AC), CxtI(Q.CxtI), DT(Q.DT), ORE(Q.ORE),
NumExcluded(Q.NumExcluded) {
Excluded = Q.Excluded;
Excluded[NumExcluded++] = NewExcl;
assert(NumExcluded <= Excluded.size());
}
bool isExcluded(const Value *Value) const {
if (NumExcluded == 0)
return false;
auto End = Excluded.begin() + NumExcluded;
return std::find(Excluded.begin(), End, Value) != End;
}
};
} // end anonymous namespace
// Given the provided Value and, potentially, a context instruction, return
// the preferred context instruction (if any).
static const Instruction *safeCxtI(const Value *V, const Instruction *CxtI) {
// If we've been provided with a context instruction, then use that (provided
// it has been inserted).
if (CxtI && CxtI->getParent())
return CxtI;
// If the value is really an already-inserted instruction, then use that.
CxtI = dyn_cast<Instruction>(V);
if (CxtI && CxtI->getParent())
return CxtI;
return nullptr;
}
static void computeKnownBits(const Value *V, APInt &KnownZero, APInt &KnownOne,
unsigned Depth, const Query &Q);
void llvm::computeKnownBits(const Value *V, APInt &KnownZero, APInt &KnownOne,
const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT,
OptimizationRemarkEmitter *ORE) {
::computeKnownBits(V, KnownZero, KnownOne, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT, ORE));
}
bool llvm::haveNoCommonBitsSet(const Value *LHS, const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
assert(LHS->getType() == RHS->getType() &&
"LHS and RHS should have the same type");
assert(LHS->getType()->isIntOrIntVectorTy() &&
"LHS and RHS should be integers");
IntegerType *IT = cast<IntegerType>(LHS->getType()->getScalarType());
APInt LHSKnownZero(IT->getBitWidth(), 0), LHSKnownOne(IT->getBitWidth(), 0);
APInt RHSKnownZero(IT->getBitWidth(), 0), RHSKnownOne(IT->getBitWidth(), 0);
computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, 0, AC, CxtI, DT);
computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, 0, AC, CxtI, DT);
return (LHSKnownZero | RHSKnownZero).isAllOnesValue();
}
static void ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
unsigned Depth, const Query &Q);
void llvm::ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
::ComputeSignBit(V, KnownZero, KnownOne, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT));
}
static bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
const Query &Q);
bool llvm::isKnownToBeAPowerOfTwo(const Value *V, const DataLayout &DL,
bool OrZero,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
return ::isKnownToBeAPowerOfTwo(V, OrZero, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT));
}
static bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q);
bool llvm::isKnownNonZero(const Value *V, const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
return ::isKnownNonZero(V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT));
}
bool llvm::isKnownNonNegative(const Value *V, const DataLayout &DL,
unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
bool NonNegative, Negative;
ComputeSignBit(V, NonNegative, Negative, DL, Depth, AC, CxtI, DT);
return NonNegative;
}
bool llvm::isKnownPositive(const Value *V, const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
if (auto *CI = dyn_cast<ConstantInt>(V))
return CI->getValue().isStrictlyPositive();
// TODO: We'd doing two recursive queries here. We should factor this such
// that only a single query is needed.
return isKnownNonNegative(V, DL, Depth, AC, CxtI, DT) &&
isKnownNonZero(V, DL, Depth, AC, CxtI, DT);
}
bool llvm::isKnownNegative(const Value *V, const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
bool NonNegative, Negative;
ComputeSignBit(V, NonNegative, Negative, DL, Depth, AC, CxtI, DT);
return Negative;
}
static bool isKnownNonEqual(const Value *V1, const Value *V2, const Query &Q);
bool llvm::isKnownNonEqual(const Value *V1, const Value *V2,
const DataLayout &DL,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
return ::isKnownNonEqual(V1, V2, Query(DL, AC,
safeCxtI(V1, safeCxtI(V2, CxtI)),
DT));
}
static bool MaskedValueIsZero(const Value *V, const APInt &Mask, unsigned Depth,
const Query &Q);
bool llvm::MaskedValueIsZero(const Value *V, const APInt &Mask,
const DataLayout &DL,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI, const DominatorTree *DT) {
return ::MaskedValueIsZero(V, Mask, Depth,
Query(DL, AC, safeCxtI(V, CxtI), DT));
}
static unsigned ComputeNumSignBits(const Value *V, unsigned Depth,
const Query &Q);
unsigned llvm::ComputeNumSignBits(const Value *V, const DataLayout &DL,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
return ::ComputeNumSignBits(V, Depth, Query(DL, AC, safeCxtI(V, CxtI), DT));
}
static void computeKnownBitsAddSub(bool Add, const Value *Op0, const Value *Op1,
bool NSW,
APInt &KnownZero, APInt &KnownOne,
APInt &KnownZero2, APInt &KnownOne2,
unsigned Depth, const Query &Q) {
if (!Add) {
if (const ConstantInt *CLHS = dyn_cast<ConstantInt>(Op0)) {
// We know that the top bits of C-X are clear if X contains less bits
// than C (i.e. no wrap-around can happen). For example, 20-X is
// positive if we can prove that X is >= 0 and < 16.
if (!CLHS->getValue().isNegative()) {
unsigned BitWidth = KnownZero.getBitWidth();
unsigned NLZ = (CLHS->getValue()+1).countLeadingZeros();
// NLZ can't be BitWidth with no sign bit
APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
computeKnownBits(Op1, KnownZero2, KnownOne2, Depth + 1, Q);
// If all of the MaskV bits are known to be zero, then we know the
// output top bits are zero, because we now know that the output is
// from [0-C].
if ((KnownZero2 & MaskV) == MaskV) {
unsigned NLZ2 = CLHS->getValue().countLeadingZeros();
// Top bits known zero.
KnownZero = APInt::getHighBitsSet(BitWidth, NLZ2);
}
}
}
}
unsigned BitWidth = KnownZero.getBitWidth();
// If an initial sequence of bits in the result is not needed, the
// corresponding bits in the operands are not needed.
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
computeKnownBits(Op0, LHSKnownZero, LHSKnownOne, Depth + 1, Q);
computeKnownBits(Op1, KnownZero2, KnownOne2, Depth + 1, Q);
// Carry in a 1 for a subtract, rather than a 0.
APInt CarryIn(BitWidth, 0);
if (!Add) {
// Sum = LHS + ~RHS + 1
std::swap(KnownZero2, KnownOne2);
CarryIn.setBit(0);
}
APInt PossibleSumZero = ~LHSKnownZero + ~KnownZero2 + CarryIn;
APInt PossibleSumOne = LHSKnownOne + KnownOne2 + CarryIn;
// Compute known bits of the carry.
APInt CarryKnownZero = ~(PossibleSumZero ^ LHSKnownZero ^ KnownZero2);
APInt CarryKnownOne = PossibleSumOne ^ LHSKnownOne ^ KnownOne2;
// Compute set of known bits (where all three relevant bits are known).
APInt LHSKnown = LHSKnownZero | LHSKnownOne;
APInt RHSKnown = KnownZero2 | KnownOne2;
APInt CarryKnown = CarryKnownZero | CarryKnownOne;
APInt Known = LHSKnown & RHSKnown & CarryKnown;
assert((PossibleSumZero & Known) == (PossibleSumOne & Known) &&
"known bits of sum differ");
// Compute known bits of the result.
KnownZero = ~PossibleSumOne & Known;
KnownOne = PossibleSumOne & Known;
// Are we still trying to solve for the sign bit?
if (!Known.isNegative()) {
if (NSW) {
// Adding two non-negative numbers, or subtracting a negative number from
// a non-negative one, can't wrap into negative.
if (LHSKnownZero.isNegative() && KnownZero2.isNegative())
KnownZero |= APInt::getSignBit(BitWidth);
// Adding two negative numbers, or subtracting a non-negative number from
// a negative one, can't wrap into non-negative.
else if (LHSKnownOne.isNegative() && KnownOne2.isNegative())
KnownOne |= APInt::getSignBit(BitWidth);
}
}
}
static void computeKnownBitsMul(const Value *Op0, const Value *Op1, bool NSW,
APInt &KnownZero, APInt &KnownOne,
APInt &KnownZero2, APInt &KnownOne2,
unsigned Depth, const Query &Q) {
unsigned BitWidth = KnownZero.getBitWidth();
computeKnownBits(Op1, KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(Op0, KnownZero2, KnownOne2, Depth + 1, Q);
bool isKnownNegative = false;
bool isKnownNonNegative = false;
// If the multiplication is known not to overflow, compute the sign bit.
if (NSW) {
if (Op0 == Op1) {
// The product of a number with itself is non-negative.
isKnownNonNegative = true;
} else {
bool isKnownNonNegativeOp1 = KnownZero.isNegative();
bool isKnownNonNegativeOp0 = KnownZero2.isNegative();
bool isKnownNegativeOp1 = KnownOne.isNegative();
bool isKnownNegativeOp0 = KnownOne2.isNegative();
// The product of two numbers with the same sign is non-negative.
isKnownNonNegative = (isKnownNegativeOp1 && isKnownNegativeOp0) ||
(isKnownNonNegativeOp1 && isKnownNonNegativeOp0);
// The product of a negative number and a non-negative number is either
// negative or zero.
if (!isKnownNonNegative)
isKnownNegative = (isKnownNegativeOp1 && isKnownNonNegativeOp0 &&
isKnownNonZero(Op0, Depth, Q)) ||
(isKnownNegativeOp0 && isKnownNonNegativeOp1 &&
isKnownNonZero(Op1, Depth, Q));
}
}
// If low bits are zero in either operand, output low known-0 bits.
// Also compute a conservative estimate for high known-0 bits.
// More trickiness is possible, but this is sufficient for the
// interesting case of alignment computation.
KnownOne.clearAllBits();
unsigned TrailZ = KnownZero.countTrailingOnes() +
KnownZero2.countTrailingOnes();
unsigned LeadZ = std::max(KnownZero.countLeadingOnes() +
KnownZero2.countLeadingOnes(),
BitWidth) - BitWidth;
TrailZ = std::min(TrailZ, BitWidth);
LeadZ = std::min(LeadZ, BitWidth);
KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ) |
APInt::getHighBitsSet(BitWidth, LeadZ);
// Only make use of no-wrap flags if we failed to compute the sign bit
// directly. This matters if the multiplication always overflows, in
// which case we prefer to follow the result of the direct computation,
// though as the program is invoking undefined behaviour we can choose
// whatever we like here.
if (isKnownNonNegative && !KnownOne.isNegative())
KnownZero.setBit(BitWidth - 1);
else if (isKnownNegative && !KnownZero.isNegative())
KnownOne.setBit(BitWidth - 1);
}
void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
APInt &KnownZero,
APInt &KnownOne) {
unsigned BitWidth = KnownZero.getBitWidth();
unsigned NumRanges = Ranges.getNumOperands() / 2;
assert(NumRanges >= 1);
KnownZero.setAllBits();
KnownOne.setAllBits();
for (unsigned i = 0; i < NumRanges; ++i) {
ConstantInt *Lower =
mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0));
ConstantInt *Upper =
mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1));
ConstantRange Range(Lower->getValue(), Upper->getValue());
// The first CommonPrefixBits of all values in Range are equal.
unsigned CommonPrefixBits =
(Range.getUnsignedMax() ^ Range.getUnsignedMin()).countLeadingZeros();
APInt Mask = APInt::getHighBitsSet(BitWidth, CommonPrefixBits);
KnownOne &= Range.getUnsignedMax() & Mask;
KnownZero &= ~Range.getUnsignedMax() & Mask;
}
}
static bool isEphemeralValueOf(const Instruction *I, const Value *E) {
SmallVector<const Value *, 16> WorkSet(1, I);
SmallPtrSet<const Value *, 32> Visited;
SmallPtrSet<const Value *, 16> EphValues;
// The instruction defining an assumption's condition itself is always
// considered ephemeral to that assumption (even if it has other
// non-ephemeral users). See r246696's test case for an example.
if (is_contained(I->operands(), E))
return true;
while (!WorkSet.empty()) {
const Value *V = WorkSet.pop_back_val();
if (!Visited.insert(V).second)
continue;
// If all uses of this value are ephemeral, then so is this value.
if (all_of(V->users(), [&](const User *U) { return EphValues.count(U); })) {
if (V == E)
return true;
EphValues.insert(V);
if (const User *U = dyn_cast<User>(V))
for (User::const_op_iterator J = U->op_begin(), JE = U->op_end();
J != JE; ++J) {
if (isSafeToSpeculativelyExecute(*J))
WorkSet.push_back(*J);
}
}
}
return false;
}
// Is this an intrinsic that cannot be speculated but also cannot trap?
static bool isAssumeLikeIntrinsic(const Instruction *I) {
if (const CallInst *CI = dyn_cast<CallInst>(I))
if (Function *F = CI->getCalledFunction())
switch (F->getIntrinsicID()) {
default: break;
// FIXME: This list is repeated from NoTTI::getIntrinsicCost.
case Intrinsic::assume:
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
case Intrinsic::invariant_start:
case Intrinsic::invariant_end:
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
case Intrinsic::objectsize:
case Intrinsic::ptr_annotation:
case Intrinsic::var_annotation:
return true;
}
return false;
}
bool llvm::isValidAssumeForContext(const Instruction *Inv,
const Instruction *CxtI,
const DominatorTree *DT) {
// There are two restrictions on the use of an assume:
// 1. The assume must dominate the context (or the control flow must
// reach the assume whenever it reaches the context).
// 2. The context must not be in the assume's set of ephemeral values
// (otherwise we will use the assume to prove that the condition
// feeding the assume is trivially true, thus causing the removal of
// the assume).
if (DT) {
if (DT->dominates(Inv, CxtI))
return true;
} else if (Inv->getParent() == CxtI->getParent()->getSinglePredecessor()) {
// We don't have a DT, but this trivially dominates.
return true;
}
// With or without a DT, the only remaining case we will check is if the
// instructions are in the same BB. Give up if that is not the case.
if (Inv->getParent() != CxtI->getParent())
return false;
// If we have a dom tree, then we now know that the assume doens't dominate
// the other instruction. If we don't have a dom tree then we can check if
// the assume is first in the BB.
if (!DT) {
// Search forward from the assume until we reach the context (or the end
// of the block); the common case is that the assume will come first.
for (auto I = std::next(BasicBlock::const_iterator(Inv)),
IE = Inv->getParent()->end(); I != IE; ++I)
if (&*I == CxtI)
return true;
}
// The context comes first, but they're both in the same block. Make sure
// there is nothing in between that might interrupt the control flow.
for (BasicBlock::const_iterator I =
std::next(BasicBlock::const_iterator(CxtI)), IE(Inv);
I != IE; ++I)
if (!isSafeToSpeculativelyExecute(&*I) && !isAssumeLikeIntrinsic(&*I))
return false;
return !isEphemeralValueOf(Inv, CxtI);
}
static void computeKnownBitsFromAssume(const Value *V, APInt &KnownZero,
APInt &KnownOne, unsigned Depth,
const Query &Q) {
// Use of assumptions is context-sensitive. If we don't have a context, we
// cannot use them!
if (!Q.AC || !Q.CxtI)
return;
unsigned BitWidth = KnownZero.getBitWidth();
// Note that the patterns below need to be kept in sync with the code
// in AssumptionCache::updateAffectedValues.
for (auto &AssumeVH : Q.AC->assumptionsFor(V)) {
if (!AssumeVH)
continue;
CallInst *I = cast<CallInst>(AssumeVH);
assert(I->getParent()->getParent() == Q.CxtI->getParent()->getParent() &&
"Got assumption for the wrong function!");
if (Q.isExcluded(I))
continue;
// Warning: This loop can end up being somewhat performance sensetive.
// We're running this loop for once for each value queried resulting in a
// runtime of ~O(#assumes * #values).
assert(I->getCalledFunction()->getIntrinsicID() == Intrinsic::assume &&
"must be an assume intrinsic");
Value *Arg = I->getArgOperand(0);
if (Arg == V && isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
assert(BitWidth == 1 && "assume operand is not i1?");
KnownZero.clearAllBits();
KnownOne.setAllBits();
return;
}
if (match(Arg, m_Not(m_Specific(V))) &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
assert(BitWidth == 1 && "assume operand is not i1?");
KnownZero.setAllBits();
KnownOne.clearAllBits();
return;
}
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth == MaxDepth)
continue;
Value *A, *B;
auto m_V = m_CombineOr(m_Specific(V),
m_CombineOr(m_PtrToInt(m_Specific(V)),
m_BitCast(m_Specific(V))));
CmpInst::Predicate Pred;
ConstantInt *C;
// assume(v = a)
if (match(Arg, m_c_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ && isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
KnownZero |= RHSKnownZero;
KnownOne |= RHSKnownOne;
// assume(v & b = a)
} else if (match(Arg,
m_c_ICmp(Pred, m_c_And(m_V, m_Value(B)), m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
computeKnownBits(B, MaskKnownZero, MaskKnownOne, Depth+1, Query(Q, I));
// For those bits in the mask that are known to be one, we can propagate
// known bits from the RHS to V.
KnownZero |= RHSKnownZero & MaskKnownOne;
KnownOne |= RHSKnownOne & MaskKnownOne;
// assume(~(v & b) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_And(m_V, m_Value(B))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
APInt MaskKnownZero(BitWidth, 0), MaskKnownOne(BitWidth, 0);
computeKnownBits(B, MaskKnownZero, MaskKnownOne, Depth+1, Query(Q, I));
// For those bits in the mask that are known to be one, we can propagate
// inverted known bits from the RHS to V.
KnownZero |= RHSKnownOne & MaskKnownOne;
KnownOne |= RHSKnownZero & MaskKnownOne;
// assume(v | b = a)
} else if (match(Arg,
m_c_ICmp(Pred, m_c_Or(m_V, m_Value(B)), m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate known
// bits from the RHS to V.
KnownZero |= RHSKnownZero & BKnownZero;
KnownOne |= RHSKnownOne & BKnownZero;
// assume(~(v | b) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Or(m_V, m_Value(B))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate
// inverted known bits from the RHS to V.
KnownZero |= RHSKnownOne & BKnownZero;
KnownOne |= RHSKnownZero & BKnownZero;
// assume(v ^ b = a)
} else if (match(Arg,
m_c_ICmp(Pred, m_c_Xor(m_V, m_Value(B)), m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate known
// bits from the RHS to V. For those bits in B that are known to be one,
// we can propagate inverted known bits from the RHS to V.
KnownZero |= RHSKnownZero & BKnownZero;
KnownOne |= RHSKnownOne & BKnownZero;
KnownZero |= RHSKnownOne & BKnownOne;
KnownOne |= RHSKnownZero & BKnownOne;
// assume(~(v ^ b) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_c_Xor(m_V, m_Value(B))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
APInt BKnownZero(BitWidth, 0), BKnownOne(BitWidth, 0);
computeKnownBits(B, BKnownZero, BKnownOne, Depth+1, Query(Q, I));
// For those bits in B that are known to be zero, we can propagate
// inverted known bits from the RHS to V. For those bits in B that are
// known to be one, we can propagate known bits from the RHS to V.
KnownZero |= RHSKnownOne & BKnownZero;
KnownOne |= RHSKnownZero & BKnownZero;
KnownZero |= RHSKnownZero & BKnownOne;
KnownOne |= RHSKnownOne & BKnownOne;
// assume(v << c = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Shl(m_V, m_ConstantInt(C)),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them to known
// bits in V shifted to the right by C.
KnownZero |= RHSKnownZero.lshr(C->getZExtValue());
KnownOne |= RHSKnownOne.lshr(C->getZExtValue());
// assume(~(v << c) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_Shl(m_V, m_ConstantInt(C))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them inverted
// to known bits in V shifted to the right by C.
KnownZero |= RHSKnownOne.lshr(C->getZExtValue());
KnownOne |= RHSKnownZero.lshr(C->getZExtValue());
// assume(v >> c = a)
} else if (match(Arg,
m_c_ICmp(Pred, m_CombineOr(m_LShr(m_V, m_ConstantInt(C)),
m_AShr(m_V, m_ConstantInt(C))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them to known
// bits in V shifted to the right by C.
KnownZero |= RHSKnownZero << C->getZExtValue();
KnownOne |= RHSKnownOne << C->getZExtValue();
// assume(~(v >> c) = a)
} else if (match(Arg, m_c_ICmp(Pred, m_Not(m_CombineOr(
m_LShr(m_V, m_ConstantInt(C)),
m_AShr(m_V, m_ConstantInt(C)))),
m_Value(A))) &&
Pred == ICmpInst::ICMP_EQ &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
// For those bits in RHS that are known, we can propagate them inverted
// to known bits in V shifted to the right by C.
KnownZero |= RHSKnownOne << C->getZExtValue();
KnownOne |= RHSKnownZero << C->getZExtValue();
// assume(v >=_s c) where c is non-negative
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SGE &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
if (RHSKnownZero.isNegative()) {
// We know that the sign bit is zero.
KnownZero |= APInt::getSignBit(BitWidth);
}
// assume(v >_s c) where c is at least -1.
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SGT &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
if (RHSKnownOne.isAllOnesValue() || RHSKnownZero.isNegative()) {
// We know that the sign bit is zero.
KnownZero |= APInt::getSignBit(BitWidth);
}
// assume(v <=_s c) where c is negative
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SLE &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
if (RHSKnownOne.isNegative()) {
// We know that the sign bit is one.
KnownOne |= APInt::getSignBit(BitWidth);
}
// assume(v <_s c) where c is non-positive
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_SLT &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
if (RHSKnownZero.isAllOnesValue() || RHSKnownOne.isNegative()) {
// We know that the sign bit is one.
KnownOne |= APInt::getSignBit(BitWidth);
}
// assume(v <=_u c)
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_ULE &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
// Whatever high bits in c are zero are known to be zero.
KnownZero |=
APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
// assume(v <_u c)
} else if (match(Arg, m_ICmp(Pred, m_V, m_Value(A))) &&
Pred == ICmpInst::ICMP_ULT &&
isValidAssumeForContext(I, Q.CxtI, Q.DT)) {
APInt RHSKnownZero(BitWidth, 0), RHSKnownOne(BitWidth, 0);
computeKnownBits(A, RHSKnownZero, RHSKnownOne, Depth+1, Query(Q, I));
// Whatever high bits in c are zero are known to be zero (if c is a power
// of 2, then one more).
if (isKnownToBeAPowerOfTwo(A, false, Depth + 1, Query(Q, I)))
KnownZero |=
APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes()+1);
else
KnownZero |=
APInt::getHighBitsSet(BitWidth, RHSKnownZero.countLeadingOnes());
}
}
// If assumptions conflict with each other or previous known bits, then we
// have a logical fallacy. It's possible that the assumption is not reachable,
// so this isn't a real bug. On the other hand, the program may have undefined
// behavior, or we might have a bug in the compiler. We can't assert/crash, so
// clear out the known bits, try to warn the user, and hope for the best.
if ((KnownZero & KnownOne) != 0) {
KnownZero.clearAllBits();
KnownOne.clearAllBits();
if (Q.ORE) {
auto *CxtI = const_cast<Instruction *>(Q.CxtI);
OptimizationRemarkAnalysis ORA("value-tracking", "BadAssumption", CxtI);
Q.ORE->emit(ORA << "Detected conflicting code assumptions. Program may "
"have undefined behavior, or compiler may have "
"internal error.");
}
}
}
// Compute known bits from a shift operator, including those with a
// non-constant shift amount. KnownZero and KnownOne are the outputs of this
// function. KnownZero2 and KnownOne2 are pre-allocated temporaries with the
// same bit width as KnownZero and KnownOne. KZF and KOF are operator-specific
// functors that, given the known-zero or known-one bits respectively, and a
// shift amount, compute the implied known-zero or known-one bits of the shift
// operator's result respectively for that shift amount. The results from calling
// KZF and KOF are conservatively combined for all permitted shift amounts.
static void computeKnownBitsFromShiftOperator(
const Operator *I, APInt &KnownZero, APInt &KnownOne, APInt &KnownZero2,
APInt &KnownOne2, unsigned Depth, const Query &Q,
function_ref<APInt(const APInt &, unsigned)> KZF,
function_ref<APInt(const APInt &, unsigned)> KOF) {
unsigned BitWidth = KnownZero.getBitWidth();
if (auto *SA = dyn_cast<ConstantInt>(I->getOperand(1))) {
unsigned ShiftAmt = SA->getLimitedValue(BitWidth-1);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
KnownZero = KZF(KnownZero, ShiftAmt);
KnownOne = KOF(KnownOne, ShiftAmt);
// If there is conflict between KnownZero and KnownOne, this must be an
// overflowing left shift, so the shift result is undefined. Clear KnownZero
// and KnownOne bits so that other code could propagate this undef.
if ((KnownZero & KnownOne) != 0) {
KnownZero.clearAllBits();
KnownOne.clearAllBits();
}
return;
}
computeKnownBits(I->getOperand(1), KnownZero, KnownOne, Depth + 1, Q);
// Note: We cannot use KnownZero.getLimitedValue() here, because if
// BitWidth > 64 and any upper bits are known, we'll end up returning the
// limit value (which implies all bits are known).
uint64_t ShiftAmtKZ = KnownZero.zextOrTrunc(64).getZExtValue();
uint64_t ShiftAmtKO = KnownOne.zextOrTrunc(64).getZExtValue();
// It would be more-clearly correct to use the two temporaries for this
// calculation. Reusing the APInts here to prevent unnecessary allocations.
KnownZero.clearAllBits();
KnownOne.clearAllBits();
// If we know the shifter operand is nonzero, we can sometimes infer more
// known bits. However this is expensive to compute, so be lazy about it and
// only compute it when absolutely necessary.
Optional<bool> ShifterOperandIsNonZero;
// Early exit if we can't constrain any well-defined shift amount.
if (!(ShiftAmtKZ & (BitWidth - 1)) && !(ShiftAmtKO & (BitWidth - 1))) {
ShifterOperandIsNonZero =
isKnownNonZero(I->getOperand(1), Depth + 1, Q);
if (!*ShifterOperandIsNonZero)
return;
}
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
KnownZero = KnownOne = APInt::getAllOnesValue(BitWidth);
for (unsigned ShiftAmt = 0; ShiftAmt < BitWidth; ++ShiftAmt) {
// Combine the shifted known input bits only for those shift amounts
// compatible with its known constraints.
if ((ShiftAmt & ~ShiftAmtKZ) != ShiftAmt)
continue;
if ((ShiftAmt | ShiftAmtKO) != ShiftAmt)
continue;
// If we know the shifter is nonzero, we may be able to infer more known
// bits. This check is sunk down as far as possible to avoid the expensive
// call to isKnownNonZero if the cheaper checks above fail.
if (ShiftAmt == 0) {
if (!ShifterOperandIsNonZero.hasValue())
ShifterOperandIsNonZero =
isKnownNonZero(I->getOperand(1), Depth + 1, Q);
if (*ShifterOperandIsNonZero)
continue;
}
KnownZero &= KZF(KnownZero2, ShiftAmt);
KnownOne &= KOF(KnownOne2, ShiftAmt);
}
// If there are no compatible shift amounts, then we've proven that the shift
// amount must be >= the BitWidth, and the result is undefined. We could
// return anything we'd like, but we need to make sure the sets of known bits
// stay disjoint (it should be better for some other code to actually
// propagate the undef than to pick a value here using known bits).
if ((KnownZero & KnownOne) != 0) {
KnownZero.clearAllBits();
KnownOne.clearAllBits();
}
}
static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
APInt &KnownOne, unsigned Depth,
const Query &Q) {
unsigned BitWidth = KnownZero.getBitWidth();
APInt KnownZero2(KnownZero), KnownOne2(KnownOne);
switch (I->getOpcode()) {
default: break;
case Instruction::Load:
if (MDNode *MD = cast<LoadInst>(I)->getMetadata(LLVMContext::MD_range))
computeKnownBitsFromRangeMetadata(*MD, KnownZero, KnownOne);
break;
case Instruction::And: {
// If either the LHS or the RHS are Zero, the result is zero.
computeKnownBits(I->getOperand(1), KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
// Output known-1 bits are only known if set in both the LHS & RHS.
KnownOne &= KnownOne2;
// Output known-0 are known to be clear if zero in either the LHS | RHS.
KnownZero |= KnownZero2;
// and(x, add (x, -1)) is a common idiom that always clears the low bit;
// here we handle the more general case of adding any odd number by
// matching the form add(x, add(x, y)) where y is odd.
// TODO: This could be generalized to clearing any bit set in y where the
// following bit is known to be unset in y.
Value *Y = nullptr;
if (match(I->getOperand(0), m_Add(m_Specific(I->getOperand(1)),
m_Value(Y))) ||
match(I->getOperand(1), m_Add(m_Specific(I->getOperand(0)),
m_Value(Y)))) {
APInt KnownZero3(BitWidth, 0), KnownOne3(BitWidth, 0);
computeKnownBits(Y, KnownZero3, KnownOne3, Depth + 1, Q);
if (KnownOne3.countTrailingOnes() > 0)
KnownZero |= APInt::getLowBitsSet(BitWidth, 1);
}
break;
}
case Instruction::Or: {
computeKnownBits(I->getOperand(1), KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
// Output known-0 bits are only known if clear in both the LHS & RHS.
KnownZero &= KnownZero2;
// Output known-1 are known to be set if set in either the LHS | RHS.
KnownOne |= KnownOne2;
break;
}
case Instruction::Xor: {
computeKnownBits(I->getOperand(1), KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
// Output known-0 bits are known if clear or set in both the LHS & RHS.
APInt KnownZeroOut = (KnownZero & KnownZero2) | (KnownOne & KnownOne2);
// Output known-1 are known to be set if set in only one of the LHS, RHS.
KnownOne = (KnownZero & KnownOne2) | (KnownOne & KnownZero2);
KnownZero = KnownZeroOut;
break;
}
case Instruction::Mul: {
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
computeKnownBitsMul(I->getOperand(0), I->getOperand(1), NSW, KnownZero,
KnownOne, KnownZero2, KnownOne2, Depth, Q);
break;
}
case Instruction::UDiv: {
// For the purposes of computing leading zeros we can conservatively
// treat a udiv as a logical right shift by the power of 2 known to
// be less than the denominator.
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
unsigned LeadZ = KnownZero2.countLeadingOnes();
KnownOne2.clearAllBits();
KnownZero2.clearAllBits();
computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, Depth + 1, Q);
unsigned RHSUnknownLeadingOnes = KnownOne2.countLeadingZeros();
if (RHSUnknownLeadingOnes != BitWidth)
LeadZ = std::min(BitWidth,
LeadZ + BitWidth - RHSUnknownLeadingOnes - 1);
KnownZero = APInt::getHighBitsSet(BitWidth, LeadZ);
break;
}
case Instruction::Select: {
computeKnownBits(I->getOperand(2), KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, Depth + 1, Q);
const Value *LHS;
const Value *RHS;
SelectPatternFlavor SPF = matchSelectPattern(I, LHS, RHS).Flavor;
if (SelectPatternResult::isMinOrMax(SPF)) {
computeKnownBits(RHS, KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(LHS, KnownZero2, KnownOne2, Depth + 1, Q);
} else {
computeKnownBits(I->getOperand(2), KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, Depth + 1, Q);
}
unsigned MaxHighOnes = 0;
unsigned MaxHighZeros = 0;
if (SPF == SPF_SMAX) {
// If both sides are negative, the result is negative.
if (KnownOne[BitWidth - 1] && KnownOne2[BitWidth - 1])
// We can derive a lower bound on the result by taking the max of the
// leading one bits.
MaxHighOnes =
std::max(KnownOne.countLeadingOnes(), KnownOne2.countLeadingOnes());
// If either side is non-negative, the result is non-negative.
else if (KnownZero[BitWidth - 1] || KnownZero2[BitWidth - 1])
MaxHighZeros = 1;
} else if (SPF == SPF_SMIN) {
// If both sides are non-negative, the result is non-negative.
if (KnownZero[BitWidth - 1] && KnownZero2[BitWidth - 1])
// We can derive an upper bound on the result by taking the max of the
// leading zero bits.
MaxHighZeros = std::max(KnownZero.countLeadingOnes(),
KnownZero2.countLeadingOnes());
// If either side is negative, the result is negative.
else if (KnownOne[BitWidth - 1] || KnownOne2[BitWidth - 1])
MaxHighOnes = 1;
} else if (SPF == SPF_UMAX) {
// We can derive a lower bound on the result by taking the max of the
// leading one bits.
MaxHighOnes =
std::max(KnownOne.countLeadingOnes(), KnownOne2.countLeadingOnes());
} else if (SPF == SPF_UMIN) {
// We can derive an upper bound on the result by taking the max of the
// leading zero bits.
MaxHighZeros =
std::max(KnownZero.countLeadingOnes(), KnownZero2.countLeadingOnes());
}
// Only known if known in both the LHS and RHS.
KnownOne &= KnownOne2;
KnownZero &= KnownZero2;
if (MaxHighOnes > 0)
KnownOne |= APInt::getHighBitsSet(BitWidth, MaxHighOnes);
if (MaxHighZeros > 0)
KnownZero |= APInt::getHighBitsSet(BitWidth, MaxHighZeros);
break;
}
case Instruction::FPTrunc:
case Instruction::FPExt:
case Instruction::FPToUI:
case Instruction::FPToSI:
case Instruction::SIToFP:
case Instruction::UIToFP:
break; // Can't work with floating point.
case Instruction::PtrToInt:
case Instruction::IntToPtr:
// Fall through and handle them the same as zext/trunc.
LLVM_FALLTHROUGH;
case Instruction::ZExt:
case Instruction::Trunc: {
Type *SrcTy = I->getOperand(0)->getType();
unsigned SrcBitWidth;
// Note that we handle pointer operands here because of inttoptr/ptrtoint
// which fall through here.
SrcBitWidth = Q.DL.getTypeSizeInBits(SrcTy->getScalarType());
assert(SrcBitWidth && "SrcBitWidth can't be zero");
KnownZero = KnownZero.zextOrTrunc(SrcBitWidth);
KnownOne = KnownOne.zextOrTrunc(SrcBitWidth);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
KnownZero = KnownZero.zextOrTrunc(BitWidth);
KnownOne = KnownOne.zextOrTrunc(BitWidth);
// Any top bits are known to be zero.
if (BitWidth > SrcBitWidth)
KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
break;
}
case Instruction::BitCast: {
Type *SrcTy = I->getOperand(0)->getType();
if ((SrcTy->isIntegerTy() || SrcTy->isPointerTy()) &&
// TODO: For now, not handling conversions like:
// (bitcast i64 %x to <2 x i32>)
!I->getType()->isVectorTy()) {
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
break;
}
break;
}
case Instruction::SExt: {
// Compute the bits in the result that are not present in the input.
unsigned SrcBitWidth = I->getOperand(0)->getType()->getScalarSizeInBits();
KnownZero = KnownZero.trunc(SrcBitWidth);
KnownOne = KnownOne.trunc(SrcBitWidth);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
KnownZero = KnownZero.zext(BitWidth);
KnownOne = KnownOne.zext(BitWidth);
// If the sign bit of the input is known set or clear, then we know the
// top bits of the result.
if (KnownZero[SrcBitWidth-1]) // Input sign bit known zero
KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
else if (KnownOne[SrcBitWidth-1]) // Input sign bit known set
KnownOne |= APInt::getHighBitsSet(BitWidth, BitWidth - SrcBitWidth);
break;
}
case Instruction::Shl: {
// (shl X, C1) & C2 == 0 iff (X & C2 >>u C1) == 0
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
auto KZF = [BitWidth, NSW](const APInt &KnownZero, unsigned ShiftAmt) {
APInt KZResult =
(KnownZero << ShiftAmt) |
APInt::getLowBitsSet(BitWidth, ShiftAmt); // Low bits known 0.
// If this shift has "nsw" keyword, then the result is either a poison
// value or has the same sign bit as the first operand.
if (NSW && KnownZero.isNegative())
KZResult.setBit(BitWidth - 1);
return KZResult;
};
auto KOF = [BitWidth, NSW](const APInt &KnownOne, unsigned ShiftAmt) {
APInt KOResult = KnownOne << ShiftAmt;
if (NSW && KnownOne.isNegative())
KOResult.setBit(BitWidth - 1);
return KOResult;
};
computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne,
KnownZero2, KnownOne2, Depth, Q, KZF,
KOF);
break;
}
case Instruction::LShr: {
// (ushr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
auto KZF = [BitWidth](const APInt &KnownZero, unsigned ShiftAmt) {
return APIntOps::lshr(KnownZero, ShiftAmt) |
// High bits known zero.
APInt::getHighBitsSet(BitWidth, ShiftAmt);
};
auto KOF = [](const APInt &KnownOne, unsigned ShiftAmt) {
return APIntOps::lshr(KnownOne, ShiftAmt);
};
computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne,
KnownZero2, KnownOne2, Depth, Q, KZF,
KOF);
break;
}
case Instruction::AShr: {
// (ashr X, C1) & C2 == 0 iff (-1 >> C1) & C2 == 0
auto KZF = [](const APInt &KnownZero, unsigned ShiftAmt) {
return APIntOps::ashr(KnownZero, ShiftAmt);
};
auto KOF = [](const APInt &KnownOne, unsigned ShiftAmt) {
return APIntOps::ashr(KnownOne, ShiftAmt);
};
computeKnownBitsFromShiftOperator(I, KnownZero, KnownOne,
KnownZero2, KnownOne2, Depth, Q, KZF,
KOF);
break;
}
case Instruction::Sub: {
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
computeKnownBitsAddSub(false, I->getOperand(0), I->getOperand(1), NSW,
KnownZero, KnownOne, KnownZero2, KnownOne2, Depth,
Q);
break;
}
case Instruction::Add: {
bool NSW = cast<OverflowingBinaryOperator>(I)->hasNoSignedWrap();
computeKnownBitsAddSub(true, I->getOperand(0), I->getOperand(1), NSW,
KnownZero, KnownOne, KnownZero2, KnownOne2, Depth,
Q);
break;
}
case Instruction::SRem:
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
APInt RA = Rem->getValue().abs();
if (RA.isPowerOf2()) {
APInt LowBits = RA - 1;
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1,
Q);
// The low bits of the first operand are unchanged by the srem.
KnownZero = KnownZero2 & LowBits;
KnownOne = KnownOne2 & LowBits;
// If the first operand is non-negative or has all low bits zero, then
// the upper bits are all zero.
if (KnownZero2[BitWidth-1] || ((KnownZero2 & LowBits) == LowBits))
KnownZero |= ~LowBits;
// If the first operand is negative and not all low bits are zero, then
// the upper bits are all one.
if (KnownOne2[BitWidth-1] && ((KnownOne2 & LowBits) != 0))
KnownOne |= ~LowBits;
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
}
}
// The sign bit is the LHS's sign bit, except when the result of the
// remainder is zero.
if (KnownZero.isNonNegative()) {
APInt LHSKnownZero(BitWidth, 0), LHSKnownOne(BitWidth, 0);
computeKnownBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth + 1,
Q);
// If it's known zero, our sign bit is also zero.
if (LHSKnownZero.isNegative())
KnownZero.setBit(BitWidth - 1);
}
break;
case Instruction::URem: {
if (ConstantInt *Rem = dyn_cast<ConstantInt>(I->getOperand(1))) {
const APInt &RA = Rem->getValue();
if (RA.isPowerOf2()) {
APInt LowBits = (RA - 1);
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
KnownZero |= ~LowBits;
KnownOne &= LowBits;
break;
}
}
// Since the result is less than or equal to either operand, any leading
// zero bits in either operand must also exist in the result.
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
computeKnownBits(I->getOperand(1), KnownZero2, KnownOne2, Depth + 1, Q);
unsigned Leaders = std::max(KnownZero.countLeadingOnes(),
KnownZero2.countLeadingOnes());
KnownOne.clearAllBits();
KnownZero = APInt::getHighBitsSet(BitWidth, Leaders);
break;
}
case Instruction::Alloca: {
const AllocaInst *AI = cast<AllocaInst>(I);
unsigned Align = AI->getAlignment();
if (Align == 0)
Align = Q.DL.getABITypeAlignment(AI->getAllocatedType());
if (Align > 0)
KnownZero = APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
break;
}
case Instruction::GetElementPtr: {
// Analyze all of the subscripts of this getelementptr instruction
// to determine if we can prove known low zero bits.
APInt LocalKnownZero(BitWidth, 0), LocalKnownOne(BitWidth, 0);
computeKnownBits(I->getOperand(0), LocalKnownZero, LocalKnownOne, Depth + 1,
Q);
unsigned TrailZ = LocalKnownZero.countTrailingOnes();
gep_type_iterator GTI = gep_type_begin(I);
for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i, ++GTI) {
Value *Index = I->getOperand(i);
if (StructType *STy = GTI.getStructTypeOrNull()) {
// Handle struct member offset arithmetic.
// Handle case when index is vector zeroinitializer
Constant *CIndex = cast<Constant>(Index);
if (CIndex->isZeroValue())
continue;
if (CIndex->getType()->isVectorTy())
Index = CIndex->getSplatValue();
unsigned Idx = cast<ConstantInt>(Index)->getZExtValue();
const StructLayout *SL = Q.DL.getStructLayout(STy);
uint64_t Offset = SL->getElementOffset(Idx);
TrailZ = std::min<unsigned>(TrailZ,
countTrailingZeros(Offset));
} else {
// Handle array index arithmetic.
Type *IndexedTy = GTI.getIndexedType();
if (!IndexedTy->isSized()) {
TrailZ = 0;
break;
}
unsigned GEPOpiBits = Index->getType()->getScalarSizeInBits();
uint64_t TypeSize = Q.DL.getTypeAllocSize(IndexedTy);
LocalKnownZero = LocalKnownOne = APInt(GEPOpiBits, 0);
computeKnownBits(Index, LocalKnownZero, LocalKnownOne, Depth + 1, Q);
TrailZ = std::min(TrailZ,
unsigned(countTrailingZeros(TypeSize) +
LocalKnownZero.countTrailingOnes()));
}
}
KnownZero = APInt::getLowBitsSet(BitWidth, TrailZ);
break;
}
case Instruction::PHI: {
const PHINode *P = cast<PHINode>(I);
// Handle the case of a simple two-predecessor recurrence PHI.
// There's a lot more that could theoretically be done here, but
// this is sufficient to catch some interesting cases.
if (P->getNumIncomingValues() == 2) {
for (unsigned i = 0; i != 2; ++i) {
Value *L = P->getIncomingValue(i);
Value *R = P->getIncomingValue(!i);
Operator *LU = dyn_cast<Operator>(L);
if (!LU)
continue;
unsigned Opcode = LU->getOpcode();
// Check for operations that have the property that if
// both their operands have low zero bits, the result
// will have low zero bits.
if (Opcode == Instruction::Add ||
Opcode == Instruction::Sub ||
Opcode == Instruction::And ||
Opcode == Instruction::Or ||
Opcode == Instruction::Mul) {
Value *LL = LU->getOperand(0);
Value *LR = LU->getOperand(1);
// Find a recurrence.
if (LL == I)
L = LR;
else if (LR == I)
L = LL;
else
break;
// Ok, we have a PHI of the form L op= R. Check for low
// zero bits.
computeKnownBits(R, KnownZero2, KnownOne2, Depth + 1, Q);
// We need to take the minimum number of known bits
APInt KnownZero3(KnownZero), KnownOne3(KnownOne);
computeKnownBits(L, KnownZero3, KnownOne3, Depth + 1, Q);
KnownZero = APInt::getLowBitsSet(
BitWidth, std::min(KnownZero2.countTrailingOnes(),
KnownZero3.countTrailingOnes()));
if (DontImproveNonNegativePhiBits)
break;
auto *OverflowOp = dyn_cast<OverflowingBinaryOperator>(LU);
if (OverflowOp && OverflowOp->hasNoSignedWrap()) {
// If initial value of recurrence is nonnegative, and we are adding
// a nonnegative number with nsw, the result can only be nonnegative
// or poison value regardless of the number of times we execute the
// add in phi recurrence. If initial value is negative and we are
// adding a negative number with nsw, the result can only be
// negative or poison value. Similar arguments apply to sub and mul.
//
// (add non-negative, non-negative) --> non-negative
// (add negative, negative) --> negative
if (Opcode == Instruction::Add) {
if (KnownZero2.isNegative() && KnownZero3.isNegative())
KnownZero.setBit(BitWidth - 1);
else if (KnownOne2.isNegative() && KnownOne3.isNegative())
KnownOne.setBit(BitWidth - 1);
}
// (sub nsw non-negative, negative) --> non-negative
// (sub nsw negative, non-negative) --> negative
else if (Opcode == Instruction::Sub && LL == I) {
if (KnownZero2.isNegative() && KnownOne3.isNegative())
KnownZero.setBit(BitWidth - 1);
else if (KnownOne2.isNegative() && KnownZero3.isNegative())
KnownOne.setBit(BitWidth - 1);
}
// (mul nsw non-negative, non-negative) --> non-negative
else if (Opcode == Instruction::Mul && KnownZero2.isNegative() &&
KnownZero3.isNegative())
KnownZero.setBit(BitWidth - 1);
}
break;
}
}
}
// Unreachable blocks may have zero-operand PHI nodes.
if (P->getNumIncomingValues() == 0)
break;
// Otherwise take the unions of the known bit sets of the operands,
// taking conservative care to avoid excessive recursion.
if (Depth < MaxDepth - 1 && !KnownZero && !KnownOne) {
// Skip if every incoming value references to ourself.
if (dyn_cast_or_null<UndefValue>(P->hasConstantValue()))
break;
KnownZero = APInt::getAllOnesValue(BitWidth);
KnownOne = APInt::getAllOnesValue(BitWidth);
for (Value *IncValue : P->incoming_values()) {
// Skip direct self references.
if (IncValue == P) continue;
KnownZero2 = APInt(BitWidth, 0);
KnownOne2 = APInt(BitWidth, 0);
// Recurse, but cap the recursion to one level, because we don't
// want to waste time spinning around in loops.
computeKnownBits(IncValue, KnownZero2, KnownOne2, MaxDepth - 1, Q);
KnownZero &= KnownZero2;
KnownOne &= KnownOne2;
// If all bits have been ruled out, there's no need to check
// more operands.
if (!KnownZero && !KnownOne)
break;
}
}
break;
}
case Instruction::Call:
case Instruction::Invoke:
// If range metadata is attached to this call, set known bits from that,
// and then intersect with known bits based on other properties of the
// function.
if (MDNode *MD = cast<Instruction>(I)->getMetadata(LLVMContext::MD_range))
computeKnownBitsFromRangeMetadata(*MD, KnownZero, KnownOne);
if (const Value *RV = ImmutableCallSite(I).getReturnedArgOperand()) {
computeKnownBits(RV, KnownZero2, KnownOne2, Depth + 1, Q);
KnownZero |= KnownZero2;
KnownOne |= KnownOne2;
}
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::bitreverse:
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
KnownZero = KnownZero2.reverseBits();
KnownOne = KnownOne2.reverseBits();
break;
case Intrinsic::bswap:
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
KnownZero |= KnownZero2.byteSwap();
KnownOne |= KnownOne2.byteSwap();
break;
case Intrinsic::ctlz:
case Intrinsic::cttz: {
unsigned LowBits = Log2_32(BitWidth)+1;
// If this call is undefined for 0, the result will be less than 2^n.
if (II->getArgOperand(1) == ConstantInt::getTrue(II->getContext()))
LowBits -= 1;
KnownZero |= APInt::getHighBitsSet(BitWidth, BitWidth - LowBits);
break;
}
case Intrinsic::ctpop: {
computeKnownBits(I->getOperand(0), KnownZero2, KnownOne2, Depth + 1, Q);
// We can bound the space the count needs. Also, bits known to be zero
// can't contribute to the population.
unsigned BitsPossiblySet = BitWidth - KnownZero2.countPopulation();
unsigned LeadingZeros =
APInt(BitWidth, BitsPossiblySet).countLeadingZeros();
assert(LeadingZeros <= BitWidth);
KnownZero |= APInt::getHighBitsSet(BitWidth, LeadingZeros);
KnownOne &= ~KnownZero;
// TODO: we could bound KnownOne using the lower bound on the number
// of bits which might be set provided by popcnt KnownOne2.
break;
}
case Intrinsic::x86_sse42_crc32_64_64:
KnownZero |= APInt::getHighBitsSet(64, 32);
break;
}
}
break;
case Instruction::ExtractElement:
// Look through extract element. At the moment we keep this simple and skip
// tracking the specific element. But at least we might find information
// valid for all elements of the vector (for example if vector is sign
// extended, shifted, etc).
computeKnownBits(I->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
break;
case Instruction::ExtractValue:
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I->getOperand(0))) {
const ExtractValueInst *EVI = cast<ExtractValueInst>(I);
if (EVI->getNumIndices() != 1) break;
if (EVI->getIndices()[0] == 0) {
switch (II->getIntrinsicID()) {
default: break;
case Intrinsic::uadd_with_overflow:
case Intrinsic::sadd_with_overflow:
computeKnownBitsAddSub(true, II->getArgOperand(0),
II->getArgOperand(1), false, KnownZero,
KnownOne, KnownZero2, KnownOne2, Depth, Q);
break;
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow:
computeKnownBitsAddSub(false, II->getArgOperand(0),
II->getArgOperand(1), false, KnownZero,
KnownOne, KnownZero2, KnownOne2, Depth, Q);
break;
case Intrinsic::umul_with_overflow:
case Intrinsic::smul_with_overflow:
computeKnownBitsMul(II->getArgOperand(0), II->getArgOperand(1), false,
KnownZero, KnownOne, KnownZero2, KnownOne2, Depth,
Q);
break;
}
}
}
}
}
/// Determine which bits of V are known to be either zero or one and return
/// them in the KnownZero/KnownOne bit sets.
///
/// NOTE: we cannot consider 'undef' to be "IsZero" here. The problem is that
/// we cannot optimize based on the assumption that it is zero without changing
/// it to be an explicit zero. If we don't change it to zero, other code could
/// optimized based on the contradictory assumption that it is non-zero.
/// Because instcombine aggressively folds operations with undef args anyway,
/// this won't lose us code quality.
///
/// This function is defined on values with integer type, values with pointer
/// type, and vectors of integers. In the case
/// where V is a vector, known zero, and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
void computeKnownBits(const Value *V, APInt &KnownZero, APInt &KnownOne,
unsigned Depth, const Query &Q) {
assert(V && "No Value?");
assert(Depth <= MaxDepth && "Limit Search Depth");
unsigned BitWidth = KnownZero.getBitWidth();
assert((V->getType()->isIntOrIntVectorTy() ||
V->getType()->getScalarType()->isPointerTy()) &&
"Not integer or pointer type!");
assert((Q.DL.getTypeSizeInBits(V->getType()->getScalarType()) == BitWidth) &&
(!V->getType()->isIntOrIntVectorTy() ||
V->getType()->getScalarSizeInBits() == BitWidth) &&
KnownZero.getBitWidth() == BitWidth &&
KnownOne.getBitWidth() == BitWidth &&
"V, KnownOne and KnownZero should have same BitWidth");
const APInt *C;
if (match(V, m_APInt(C))) {
// We know all of the bits for a scalar constant or a splat vector constant!
KnownOne = *C;
KnownZero = ~KnownOne;
return;
}
// Null and aggregate-zero are all-zeros.
if (isa<ConstantPointerNull>(V) || isa<ConstantAggregateZero>(V)) {
KnownOne.clearAllBits();
KnownZero = APInt::getAllOnesValue(BitWidth);
return;
}
// Handle a constant vector by taking the intersection of the known bits of
// each element.
if (const ConstantDataSequential *CDS = dyn_cast<ConstantDataSequential>(V)) {
// We know that CDS must be a vector of integers. Take the intersection of
// each element.
KnownZero.setAllBits(); KnownOne.setAllBits();
APInt Elt(KnownZero.getBitWidth(), 0);
for (unsigned i = 0, e = CDS->getNumElements(); i != e; ++i) {
Elt = CDS->getElementAsInteger(i);
KnownZero &= ~Elt;
KnownOne &= Elt;
}
return;
}
if (const auto *CV = dyn_cast<ConstantVector>(V)) {
// We know that CV must be a vector of integers. Take the intersection of
// each element.
KnownZero.setAllBits(); KnownOne.setAllBits();
APInt Elt(KnownZero.getBitWidth(), 0);
for (unsigned i = 0, e = CV->getNumOperands(); i != e; ++i) {
Constant *Element = CV->getAggregateElement(i);
auto *ElementCI = dyn_cast_or_null<ConstantInt>(Element);
if (!ElementCI) {
KnownZero.clearAllBits();
KnownOne.clearAllBits();
return;
}
Elt = ElementCI->getValue();
KnownZero &= ~Elt;
KnownOne &= Elt;
}
return;
}
// Start out not knowing anything.
KnownZero.clearAllBits(); KnownOne.clearAllBits();
// We can't imply anything about undefs.
if (isa<UndefValue>(V))
return;
// There's no point in looking through other users of ConstantData for
// assumptions. Confirm that we've handled them all.
assert(!isa<ConstantData>(V) && "Unhandled constant data!");
// Limit search depth.
// All recursive calls that increase depth must come after this.
if (Depth == MaxDepth)
return;
// A weak GlobalAlias is totally unknown. A non-weak GlobalAlias has
// the bits of its aliasee.
if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (!GA->isInterposable())
computeKnownBits(GA->getAliasee(), KnownZero, KnownOne, Depth + 1, Q);
return;
}
if (const Operator *I = dyn_cast<Operator>(V))
computeKnownBitsFromOperator(I, KnownZero, KnownOne, Depth, Q);
// Aligned pointers have trailing zeros - refine KnownZero set
if (V->getType()->isPointerTy()) {
unsigned Align = V->getPointerAlignment(Q.DL);
if (Align)
KnownZero |= APInt::getLowBitsSet(BitWidth, countTrailingZeros(Align));
}
// computeKnownBitsFromAssume strictly refines KnownZero and
// KnownOne. Therefore, we run them after computeKnownBitsFromOperator.
// Check whether a nearby assume intrinsic can determine some known bits.
computeKnownBitsFromAssume(V, KnownZero, KnownOne, Depth, Q);
assert((KnownZero & KnownOne) == 0 && "Bits known to be one AND zero?");
}
/// Determine whether the sign bit is known to be zero or one.
/// Convenience wrapper around computeKnownBits.
void ComputeSignBit(const Value *V, bool &KnownZero, bool &KnownOne,
unsigned Depth, const Query &Q) {
unsigned BitWidth = getBitWidth(V->getType(), Q.DL);
if (!BitWidth) {
KnownZero = false;
KnownOne = false;
return;
}
APInt ZeroBits(BitWidth, 0);
APInt OneBits(BitWidth, 0);
computeKnownBits(V, ZeroBits, OneBits, Depth, Q);
KnownOne = OneBits[BitWidth - 1];
KnownZero = ZeroBits[BitWidth - 1];
}
/// Return true if the given value is known to have exactly one
/// bit set when defined. For vectors return true if every element is known to
/// be a power of two when defined. Supports values with integer or pointer
/// types and vectors of integers.
bool isKnownToBeAPowerOfTwo(const Value *V, bool OrZero, unsigned Depth,
const Query &Q) {
if (const Constant *C = dyn_cast<Constant>(V)) {
if (C->isNullValue())
return OrZero;
const APInt *ConstIntOrConstSplatInt;
if (match(C, m_APInt(ConstIntOrConstSplatInt)))
return ConstIntOrConstSplatInt->isPowerOf2();
}
// 1 << X is clearly a power of two if the one is not shifted off the end. If
// it is shifted off the end then the result is undefined.
if (match(V, m_Shl(m_One(), m_Value())))
return true;
// (signbit) >>l X is clearly a power of two if the one is not shifted off the
// bottom. If it is shifted off the bottom then the result is undefined.
if (match(V, m_LShr(m_SignBit(), m_Value())))
return true;
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth++ == MaxDepth)
return false;
Value *X = nullptr, *Y = nullptr;
// A shift left or a logical shift right of a power of two is a power of two
// or zero.
if (OrZero && (match(V, m_Shl(m_Value(X), m_Value())) ||
match(V, m_LShr(m_Value(X), m_Value()))))
return isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q);
if (const ZExtInst *ZI = dyn_cast<ZExtInst>(V))
return isKnownToBeAPowerOfTwo(ZI->getOperand(0), OrZero, Depth, Q);
if (const SelectInst *SI = dyn_cast<SelectInst>(V))
return isKnownToBeAPowerOfTwo(SI->getTrueValue(), OrZero, Depth, Q) &&
isKnownToBeAPowerOfTwo(SI->getFalseValue(), OrZero, Depth, Q);
if (OrZero && match(V, m_And(m_Value(X), m_Value(Y)))) {
// A power of two and'd with anything is a power of two or zero.
if (isKnownToBeAPowerOfTwo(X, /*OrZero*/ true, Depth, Q) ||
isKnownToBeAPowerOfTwo(Y, /*OrZero*/ true, Depth, Q))
return true;
// X & (-X) is always a power of two or zero.
if (match(X, m_Neg(m_Specific(Y))) || match(Y, m_Neg(m_Specific(X))))
return true;
return false;
}
// Adding a power-of-two or zero to the same power-of-two or zero yields
// either the original power-of-two, a larger power-of-two or zero.
if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
const OverflowingBinaryOperator *VOBO = cast<OverflowingBinaryOperator>(V);
if (OrZero || VOBO->hasNoUnsignedWrap() || VOBO->hasNoSignedWrap()) {
if (match(X, m_And(m_Specific(Y), m_Value())) ||
match(X, m_And(m_Value(), m_Specific(Y))))
if (isKnownToBeAPowerOfTwo(Y, OrZero, Depth, Q))
return true;
if (match(Y, m_And(m_Specific(X), m_Value())) ||
match(Y, m_And(m_Value(), m_Specific(X))))
if (isKnownToBeAPowerOfTwo(X, OrZero, Depth, Q))
return true;
unsigned BitWidth = V->getType()->getScalarSizeInBits();
APInt LHSZeroBits(BitWidth, 0), LHSOneBits(BitWidth, 0);
computeKnownBits(X, LHSZeroBits, LHSOneBits, Depth, Q);
APInt RHSZeroBits(BitWidth, 0), RHSOneBits(BitWidth, 0);
computeKnownBits(Y, RHSZeroBits, RHSOneBits, Depth, Q);
// If i8 V is a power of two or zero:
// ZeroBits: 1 1 1 0 1 1 1 1
// ~ZeroBits: 0 0 0 1 0 0 0 0
if ((~(LHSZeroBits & RHSZeroBits)).isPowerOf2())
// If OrZero isn't set, we cannot give back a zero result.
// Make sure either the LHS or RHS has a bit set.
if (OrZero || RHSOneBits.getBoolValue() || LHSOneBits.getBoolValue())
return true;
}
}
// An exact divide or right shift can only shift off zero bits, so the result
// is a power of two only if the first operand is a power of two and not
// copying a sign bit (sdiv int_min, 2).
if (match(V, m_Exact(m_LShr(m_Value(), m_Value()))) ||
match(V, m_Exact(m_UDiv(m_Value(), m_Value())))) {
return isKnownToBeAPowerOfTwo(cast<Operator>(V)->getOperand(0), OrZero,
Depth, Q);
}
return false;
}
/// \brief Test whether a GEP's result is known to be non-null.
///
/// Uses properties inherent in a GEP to try to determine whether it is known
/// to be non-null.
///
/// Currently this routine does not support vector GEPs.
static bool isGEPKnownNonNull(const GEPOperator *GEP, unsigned Depth,
const Query &Q) {
if (!GEP->isInBounds() || GEP->getPointerAddressSpace() != 0)
return false;
// FIXME: Support vector-GEPs.
assert(GEP->getType()->isPointerTy() && "We only support plain pointer GEP");
// If the base pointer is non-null, we cannot walk to a null address with an
// inbounds GEP in address space zero.
if (isKnownNonZero(GEP->getPointerOperand(), Depth, Q))
return true;
// Walk the GEP operands and see if any operand introduces a non-zero offset.
// If so, then the GEP cannot produce a null pointer, as doing so would
// inherently violate the inbounds contract within address space zero.
for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
GTI != GTE; ++GTI) {
// Struct types are easy -- they must always be indexed by a constant.
if (StructType *STy = GTI.getStructTypeOrNull()) {
ConstantInt *OpC = cast<ConstantInt>(GTI.getOperand());
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = Q.DL.getStructLayout(STy);
uint64_t ElementOffset = SL->getElementOffset(ElementIdx);
if (ElementOffset > 0)
return true;
continue;
}
// If we have a zero-sized type, the index doesn't matter. Keep looping.
if (Q.DL.getTypeAllocSize(GTI.getIndexedType()) == 0)
continue;
// Fast path the constant operand case both for efficiency and so we don't
// increment Depth when just zipping down an all-constant GEP.
if (ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand())) {
if (!OpC->isZero())
return true;
continue;
}
// We post-increment Depth here because while isKnownNonZero increments it
// as well, when we pop back up that increment won't persist. We don't want
// to recurse 10k times just because we have 10k GEP operands. We don't
// bail completely out because we want to handle constant GEPs regardless
// of depth.
if (Depth++ >= MaxDepth)
continue;
if (isKnownNonZero(GTI.getOperand(), Depth, Q))
return true;
}
return false;
}
/// Does the 'Range' metadata (which must be a valid MD_range operand list)
/// ensure that the value it's attached to is never Value? 'RangeType' is
/// is the type of the value described by the range.
static bool rangeMetadataExcludesValue(const MDNode* Ranges, const APInt& Value) {
const unsigned NumRanges = Ranges->getNumOperands() / 2;
assert(NumRanges >= 1);
for (unsigned i = 0; i < NumRanges; ++i) {
ConstantInt *Lower =
mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 0));
ConstantInt *Upper =
mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 1));
ConstantRange Range(Lower->getValue(), Upper->getValue());
if (Range.contains(Value))
return false;
}
return true;
}
/// Return true if the given value is known to be non-zero when defined. For
/// vectors, return true if every element is known to be non-zero when
/// defined. For pointers, if the context instruction and dominator tree are
/// specified, perform context-sensitive analysis and return true if the
/// pointer couldn't possibly be null at the specified instruction.
/// Supports values with integer or pointer type and vectors of integers.
bool isKnownNonZero(const Value *V, unsigned Depth, const Query &Q) {
if (auto *C = dyn_cast<Constant>(V)) {
if (C->isNullValue())
return false;
if (isa<ConstantInt>(C))
// Must be non-zero due to null test above.
return true;
// For constant vectors, check that all elements are undefined or known
// non-zero to determine that the whole vector is known non-zero.
if (auto *VecTy = dyn_cast<VectorType>(C->getType())) {
for (unsigned i = 0, e = VecTy->getNumElements(); i != e; ++i) {
Constant *Elt = C->getAggregateElement(i);
if (!Elt || Elt->isNullValue())
return false;
if (!isa<UndefValue>(Elt) && !isa<ConstantInt>(Elt))
return false;
}
return true;
}
return false;
}
if (auto *I = dyn_cast<Instruction>(V)) {
if (MDNode *Ranges = I->getMetadata(LLVMContext::MD_range)) {
// If the possible ranges don't contain zero, then the value is
// definitely non-zero.
if (auto *Ty = dyn_cast<IntegerType>(V->getType())) {
const APInt ZeroValue(Ty->getBitWidth(), 0);
if (rangeMetadataExcludesValue(Ranges, ZeroValue))
return true;
}
}
}
// The remaining tests are all recursive, so bail out if we hit the limit.
if (Depth++ >= MaxDepth)
return false;
// Check for pointer simplifications.
if (V->getType()->isPointerTy()) {
if (isKnownNonNullAt(V, Q.CxtI, Q.DT))
return true;
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V))
if (isGEPKnownNonNull(GEP, Depth, Q))
return true;
}
unsigned BitWidth = getBitWidth(V->getType()->getScalarType(), Q.DL);
// X | Y != 0 if X != 0 or Y != 0.
Value *X = nullptr, *Y = nullptr;
if (match(V, m_Or(m_Value(X), m_Value(Y))))
return isKnownNonZero(X, Depth, Q) || isKnownNonZero(Y, Depth, Q);
// ext X != 0 if X != 0.
if (isa<SExtInst>(V) || isa<ZExtInst>(V))
return isKnownNonZero(cast<Instruction>(V)->getOperand(0), Depth, Q);
// shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
// if the lowest bit is shifted off the end.
if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
// shl nuw can't remove any non-zero bits.
const OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
if (BO->hasNoUnsignedWrap())
return isKnownNonZero(X, Depth, Q);
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(X, KnownZero, KnownOne, Depth, Q);
if (KnownOne[0])
return true;
}
// shr X, Y != 0 if X is negative. Note that the value of the shift is not
// defined if the sign bit is shifted off the end.
else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
// shr exact can only shift out zero bits.
const PossiblyExactOperator *BO = cast<PossiblyExactOperator>(V);
if (BO->isExact())
return isKnownNonZero(X, Depth, Q);
bool XKnownNonNegative, XKnownNegative;
ComputeSignBit(X, XKnownNonNegative, XKnownNegative, Depth, Q);
if (XKnownNegative)
return true;
// If the shifter operand is a constant, and all of the bits shifted
// out are known to be zero, and X is known non-zero then at least one
// non-zero bit must remain.
if (ConstantInt *Shift = dyn_cast<ConstantInt>(Y)) {
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(X, KnownZero, KnownOne, Depth, Q);
auto ShiftVal = Shift->getLimitedValue(BitWidth - 1);
// Is there a known one in the portion not shifted out?
if (KnownOne.countLeadingZeros() < BitWidth - ShiftVal)
return true;
// Are all the bits to be shifted out known zero?
if (KnownZero.countTrailingOnes() >= ShiftVal)
return isKnownNonZero(X, Depth, Q);
}
}
// div exact can only produce a zero if the dividend is zero.
else if (match(V, m_Exact(m_IDiv(m_Value(X), m_Value())))) {
return isKnownNonZero(X, Depth, Q);
}
// X + Y.
else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
bool XKnownNonNegative, XKnownNegative;
bool YKnownNonNegative, YKnownNegative;
ComputeSignBit(X, XKnownNonNegative, XKnownNegative, Depth, Q);
ComputeSignBit(Y, YKnownNonNegative, YKnownNegative, Depth, Q);
// If X and Y are both non-negative (as signed values) then their sum is not
// zero unless both X and Y are zero.
if (XKnownNonNegative && YKnownNonNegative)
if (isKnownNonZero(X, Depth, Q) || isKnownNonZero(Y, Depth, Q))
return true;
// If X and Y are both negative (as signed values) then their sum is not
// zero unless both X and Y equal INT_MIN.
if (BitWidth && XKnownNegative && YKnownNegative) {
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
APInt Mask = APInt::getSignedMaxValue(BitWidth);
// The sign bit of X is set. If some other bit is set then X is not equal
// to INT_MIN.
computeKnownBits(X, KnownZero, KnownOne, Depth, Q);
if ((KnownOne & Mask) != 0)
return true;
// The sign bit of Y is set. If some other bit is set then Y is not equal
// to INT_MIN.
computeKnownBits(Y, KnownZero, KnownOne, Depth, Q);
if ((KnownOne & Mask) != 0)
return true;
}
// The sum of a non-negative number and a power of two is not zero.
if (XKnownNonNegative &&
isKnownToBeAPowerOfTwo(Y, /*OrZero*/ false, Depth, Q))
return true;
if (YKnownNonNegative &&
isKnownToBeAPowerOfTwo(X, /*OrZero*/ false, Depth, Q))
return true;
}
// X * Y.
else if (match(V, m_Mul(m_Value(X), m_Value(Y)))) {
const OverflowingBinaryOperator *BO = cast<OverflowingBinaryOperator>(V);
// If X and Y are non-zero then so is X * Y as long as the multiplication
// does not overflow.
if ((BO->hasNoSignedWrap() || BO->hasNoUnsignedWrap()) &&
isKnownNonZero(X, Depth, Q) && isKnownNonZero(Y, Depth, Q))
return true;
}
// (C ? X : Y) != 0 if X != 0 and Y != 0.
else if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
if (isKnownNonZero(SI->getTrueValue(), Depth, Q) &&
isKnownNonZero(SI->getFalseValue(), Depth, Q))
return true;
}
// PHI
else if (const PHINode *PN = dyn_cast<PHINode>(V)) {
// Try and detect a recurrence that monotonically increases from a
// starting value, as these are common as induction variables.
if (PN->getNumIncomingValues() == 2) {
Value *Start = PN->getIncomingValue(0);
Value *Induction = PN->getIncomingValue(1);
if (isa<ConstantInt>(Induction) && !isa<ConstantInt>(Start))
std::swap(Start, Induction);
if (ConstantInt *C = dyn_cast<ConstantInt>(Start)) {
if (!C->isZero() && !C->isNegative()) {
ConstantInt *X;
if ((match(Induction, m_NSWAdd(m_Specific(PN), m_ConstantInt(X))) ||
match(Induction, m_NUWAdd(m_Specific(PN), m_ConstantInt(X)))) &&
!X->isNegative())
return true;
}
}
}
// Check if all incoming values are non-zero constant.
bool AllNonZeroConstants = all_of(PN->operands(), [](Value *V) {
return isa<ConstantInt>(V) && !cast<ConstantInt>(V)->isZeroValue();
});
if (AllNonZeroConstants)
return true;
}
if (!BitWidth) return false;
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(V, KnownZero, KnownOne, Depth, Q);
return KnownOne != 0;
}
/// Return true if V2 == V1 + X, where X is known non-zero.
static bool isAddOfNonZero(const Value *V1, const Value *V2, const Query &Q) {
const BinaryOperator *BO = dyn_cast<BinaryOperator>(V1);
if (!BO || BO->getOpcode() != Instruction::Add)
return false;
Value *Op = nullptr;
if (V2 == BO->getOperand(0))
Op = BO->getOperand(1);
else if (V2 == BO->getOperand(1))
Op = BO->getOperand(0);
else
return false;
return isKnownNonZero(Op, 0, Q);
}
/// Return true if it is known that V1 != V2.
static bool isKnownNonEqual(const Value *V1, const Value *V2, const Query &Q) {
if (V1->getType()->isVectorTy() || V1 == V2)
return false;
if (V1->getType() != V2->getType())
// We can't look through casts yet.
return false;
if (isAddOfNonZero(V1, V2, Q) || isAddOfNonZero(V2, V1, Q))
return true;
if (IntegerType *Ty = dyn_cast<IntegerType>(V1->getType())) {
// Are any known bits in V1 contradictory to known bits in V2? If V1
// has a known zero where V2 has a known one, they must not be equal.
auto BitWidth = Ty->getBitWidth();
APInt KnownZero1(BitWidth, 0);
APInt KnownOne1(BitWidth, 0);
computeKnownBits(V1, KnownZero1, KnownOne1, 0, Q);
APInt KnownZero2(BitWidth, 0);
APInt KnownOne2(BitWidth, 0);
computeKnownBits(V2, KnownZero2, KnownOne2, 0, Q);
auto OppositeBits = (KnownZero1 & KnownOne2) | (KnownZero2 & KnownOne1);
if (OppositeBits.getBoolValue())
return true;
}
return false;
}
/// Return true if 'V & Mask' is known to be zero. We use this predicate to
/// simplify operations downstream. Mask is known to be zero for bits that V
/// cannot have.
///
/// This function is defined on values with integer type, values with pointer
/// type, and vectors of integers. In the case
/// where V is a vector, the mask, known zero, and known one values are the
/// same width as the vector element, and the bit is set only if it is true
/// for all of the elements in the vector.
bool MaskedValueIsZero(const Value *V, const APInt &Mask, unsigned Depth,
const Query &Q) {
APInt KnownZero(Mask.getBitWidth(), 0), KnownOne(Mask.getBitWidth(), 0);
computeKnownBits(V, KnownZero, KnownOne, Depth, Q);
return (KnownZero & Mask) == Mask;
}
/// For vector constants, loop over the elements and find the constant with the
/// minimum number of sign bits. Return 0 if the value is not a vector constant
/// or if any element was not analyzed; otherwise, return the count for the
/// element with the minimum number of sign bits.
static unsigned computeNumSignBitsVectorConstant(const Value *V,
unsigned TyBits) {
const auto *CV = dyn_cast<Constant>(V);
if (!CV || !CV->getType()->isVectorTy())
return 0;
unsigned MinSignBits = TyBits;
unsigned NumElts = CV->getType()->getVectorNumElements();
for (unsigned i = 0; i != NumElts; ++i) {
// If we find a non-ConstantInt, bail out.
auto *Elt = dyn_cast_or_null<ConstantInt>(CV->getAggregateElement(i));
if (!Elt)
return 0;
// If the sign bit is 1, flip the bits, so we always count leading zeros.
APInt EltVal = Elt->getValue();
if (EltVal.isNegative())
EltVal = ~EltVal;
MinSignBits = std::min(MinSignBits, EltVal.countLeadingZeros());
}
return MinSignBits;
}
static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth,
const Query &Q);
static unsigned ComputeNumSignBits(const Value *V, unsigned Depth,
const Query &Q) {
unsigned Result = ComputeNumSignBitsImpl(V, Depth, Q);
assert(Result > 0 && "At least one sign bit needs to be present!");
return Result;
}
/// Return the number of times the sign bit of the register is replicated into
/// the other bits. We know that at least 1 bit is always equal to the sign bit
/// (itself), but other cases can give us information. For example, immediately
/// after an "ashr X, 2", we know that the top 3 bits are all equal to each
/// other, so we return 3. For vectors, return the number of sign bits for the
/// vector element with the mininum number of known sign bits.
static unsigned ComputeNumSignBitsImpl(const Value *V, unsigned Depth,
const Query &Q) {
// We return the minimum number of sign bits that are guaranteed to be present
// in V, so for undef we have to conservatively return 1. We don't have the
// same behavior for poison though -- that's a FIXME today.
unsigned TyBits = Q.DL.getTypeSizeInBits(V->getType()->getScalarType());
unsigned Tmp, Tmp2;
unsigned FirstAnswer = 1;
// Note that ConstantInt is handled by the general computeKnownBits case
// below.
if (Depth == MaxDepth)
return 1; // Limit search depth.
const Operator *U = dyn_cast<Operator>(V);
switch (Operator::getOpcode(V)) {
default: break;
case Instruction::SExt:
Tmp = TyBits - U->getOperand(0)->getType()->getScalarSizeInBits();
return ComputeNumSignBits(U->getOperand(0), Depth + 1, Q) + Tmp;
case Instruction::SDiv: {
const APInt *Denominator;
// sdiv X, C -> adds log(C) sign bits.
if (match(U->getOperand(1), m_APInt(Denominator))) {
// Ignore non-positive denominator.
if (!Denominator->isStrictlyPositive())
break;
// Calculate the incoming numerator bits.
unsigned NumBits = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
// Add floor(log(C)) bits to the numerator bits.
return std::min(TyBits, NumBits + Denominator->logBase2());
}
break;
}
case Instruction::SRem: {
const APInt *Denominator;
// srem X, C -> we know that the result is within [-C+1,C) when C is a
// positive constant. This let us put a lower bound on the number of sign
// bits.
if (match(U->getOperand(1), m_APInt(Denominator))) {
// Ignore non-positive denominator.
if (!Denominator->isStrictlyPositive())
break;
// Calculate the incoming numerator bits. SRem by a positive constant
// can't lower the number of sign bits.
unsigned NumrBits =
ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
// Calculate the leading sign bit constraints by examining the
// denominator. Given that the denominator is positive, there are two
// cases:
//
// 1. the numerator is positive. The result range is [0,C) and [0,C) u<
// (1 << ceilLogBase2(C)).
//
// 2. the numerator is negative. Then the result range is (-C,0] and
// integers in (-C,0] are either 0 or >u (-1 << ceilLogBase2(C)).
//
// Thus a lower bound on the number of sign bits is `TyBits -
// ceilLogBase2(C)`.
unsigned ResBits = TyBits - Denominator->ceilLogBase2();
return std::max(NumrBits, ResBits);
}
break;
}
case Instruction::AShr: {
Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
// ashr X, C -> adds C sign bits. Vectors too.
const APInt *ShAmt;
if (match(U->getOperand(1), m_APInt(ShAmt))) {
unsigned ShAmtLimited = ShAmt->getZExtValue();
if (ShAmtLimited >= TyBits)
break; // Bad shift.
Tmp += ShAmtLimited;
if (Tmp > TyBits) Tmp = TyBits;
}
return Tmp;
}
case Instruction::Shl: {
const APInt *ShAmt;
if (match(U->getOperand(1), m_APInt(ShAmt))) {
// shl destroys sign bits.
Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
Tmp2 = ShAmt->getZExtValue();
if (Tmp2 >= TyBits || // Bad shift.
Tmp2 >= Tmp) break; // Shifted all sign bits out.
return Tmp - Tmp2;
}
break;
}
case Instruction::And:
case Instruction::Or:
case Instruction::Xor: // NOT is handled here.
// Logical binary ops preserve the number of sign bits at the worst.
Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
if (Tmp != 1) {
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
FirstAnswer = std::min(Tmp, Tmp2);
// We computed what we know about the sign bits as our first
// answer. Now proceed to the generic code that uses
// computeKnownBits, and pick whichever answer is better.
}
break;
case Instruction::Select:
Tmp = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (Tmp == 1) return 1; // Early out.
Tmp2 = ComputeNumSignBits(U->getOperand(2), Depth + 1, Q);
return std::min(Tmp, Tmp2);
case Instruction::Add:
// Add can have at most one carry bit. Thus we know that the output
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
if (Tmp == 1) return 1; // Early out.
// Special case decrementing a value (ADD X, -1):
if (const auto *CRHS = dyn_cast<Constant>(U->getOperand(1)))
if (CRHS->isAllOnesValue()) {
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
computeKnownBits(U->getOperand(0), KnownZero, KnownOne, Depth + 1, Q);
// If the input is known to be 0 or 1, the output is 0/-1, which is all
// sign bits set.
if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
return TyBits;
// If we are subtracting one from a positive number, there is no carry
// out of the result.
if (KnownZero.isNegative())
return Tmp;
}
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (Tmp2 == 1) return 1;
return std::min(Tmp, Tmp2)-1;
case Instruction::Sub:
Tmp2 = ComputeNumSignBits(U->getOperand(1), Depth + 1, Q);
if (Tmp2 == 1) return 1;
// Handle NEG.
if (const auto *CLHS = dyn_cast<Constant>(U->getOperand(0)))
if (CLHS->isNullValue()) {
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
computeKnownBits(U->getOperand(1), KnownZero, KnownOne, Depth + 1, Q);
// If the input is known to be 0 or 1, the output is 0/-1, which is all
// sign bits set.
if ((KnownZero | APInt(TyBits, 1)).isAllOnesValue())
return TyBits;
// If the input is known to be positive (the sign bit is known clear),
// the output of the NEG has the same number of sign bits as the input.
if (KnownZero.isNegative())
return Tmp2;
// Otherwise, we treat this like a SUB.
}
// Sub can have at most one carry bit. Thus we know that the output
// is, at worst, one more bit than the inputs.
Tmp = ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
if (Tmp == 1) return 1; // Early out.
return std::min(Tmp, Tmp2)-1;
case Instruction::PHI: {
const PHINode *PN = cast<PHINode>(U);
unsigned NumIncomingValues = PN->getNumIncomingValues();
// Don't analyze large in-degree PHIs.
if (NumIncomingValues > 4) break;
// Unreachable blocks may have zero-operand PHI nodes.
if (NumIncomingValues == 0) break;
// Take the minimum of all incoming values. This can't infinitely loop
// because of our depth threshold.
Tmp = ComputeNumSignBits(PN->getIncomingValue(0), Depth + 1, Q);
for (unsigned i = 1, e = NumIncomingValues; i != e; ++i) {
if (Tmp == 1) return Tmp;
Tmp = std::min(
Tmp, ComputeNumSignBits(PN->getIncomingValue(i), Depth + 1, Q));
}
return Tmp;
}
case Instruction::Trunc:
// FIXME: it's tricky to do anything useful for this, but it is an important
// case for targets like X86.
break;
case Instruction::ExtractElement:
// Look through extract element. At the moment we keep this simple and skip
// tracking the specific element. But at least we might find information
// valid for all elements of the vector (for example if vector is sign
// extended, shifted, etc).
return ComputeNumSignBits(U->getOperand(0), Depth + 1, Q);
}
// Finally, if we can prove that the top bits of the result are 0's or 1's,
// use this information.
// If we can examine all elements of a vector constant successfully, we're
// done (we can't do any better than that). If not, keep trying.
if (unsigned VecSignBits = computeNumSignBitsVectorConstant(V, TyBits))
return VecSignBits;
APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
computeKnownBits(V, KnownZero, KnownOne, Depth, Q);
// If we know that the sign bit is either zero or one, determine the number of
// identical bits in the top of the input value.
if (KnownZero.isNegative())
return std::max(FirstAnswer, KnownZero.countLeadingOnes());
if (KnownOne.isNegative())
return std::max(FirstAnswer, KnownOne.countLeadingOnes());
// computeKnownBits gave us no extra information about the top bits.
return FirstAnswer;
}
/// This function computes the integer multiple of Base that equals V.
/// If successful, it returns true and returns the multiple in
/// Multiple. If unsuccessful, it returns false. It looks
/// through SExt instructions only if LookThroughSExt is true.
bool llvm::ComputeMultiple(Value *V, unsigned Base, Value *&Multiple,
bool LookThroughSExt, unsigned Depth) {
const unsigned MaxDepth = 6;
assert(V && "No Value?");
assert(Depth <= MaxDepth && "Limit Search Depth");
assert(V->getType()->isIntegerTy() && "Not integer or pointer type!");
Type *T = V->getType();
ConstantInt *CI = dyn_cast<ConstantInt>(V);
if (Base == 0)
return false;
if (Base == 1) {
Multiple = V;
return true;
}
ConstantExpr *CO = dyn_cast<ConstantExpr>(V);
Constant *BaseVal = ConstantInt::get(T, Base);
if (CO && CO == BaseVal) {
// Multiple is 1.
Multiple = ConstantInt::get(T, 1);
return true;
}
if (CI && CI->getZExtValue() % Base == 0) {
Multiple = ConstantInt::get(T, CI->getZExtValue() / Base);
return true;
}
if (Depth == MaxDepth) return false; // Limit search depth.
Operator *I = dyn_cast<Operator>(V);
if (!I) return false;
switch (I->getOpcode()) {
default: break;
case Instruction::SExt:
if (!LookThroughSExt) return false;
// otherwise fall through to ZExt
case Instruction::ZExt:
return ComputeMultiple(I->getOperand(0), Base, Multiple,
LookThroughSExt, Depth+1);
case Instruction::Shl:
case Instruction::Mul: {
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
if (I->getOpcode() == Instruction::Shl) {
ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1);
if (!Op1CI) return false;
// Turn Op0 << Op1 into Op0 * 2^Op1
APInt Op1Int = Op1CI->getValue();
uint64_t BitToSet = Op1Int.getLimitedValue(Op1Int.getBitWidth() - 1);
APInt API(Op1Int.getBitWidth(), 0);
API.setBit(BitToSet);
Op1 = ConstantInt::get(V->getContext(), API);
}
Value *Mul0 = nullptr;
if (ComputeMultiple(Op0, Base, Mul0, LookThroughSExt, Depth+1)) {
if (Constant *Op1C = dyn_cast<Constant>(Op1))
if (Constant *MulC = dyn_cast<Constant>(Mul0)) {
if (Op1C->getType()->getPrimitiveSizeInBits() <
MulC->getType()->getPrimitiveSizeInBits())
Op1C = ConstantExpr::getZExt(Op1C, MulC->getType());
if (Op1C->getType()->getPrimitiveSizeInBits() >
MulC->getType()->getPrimitiveSizeInBits())
MulC = ConstantExpr::getZExt(MulC, Op1C->getType());
// V == Base * (Mul0 * Op1), so return (Mul0 * Op1)
Multiple = ConstantExpr::getMul(MulC, Op1C);
return true;
}
if (ConstantInt *Mul0CI = dyn_cast<ConstantInt>(Mul0))
if (Mul0CI->getValue() == 1) {
// V == Base * Op1, so return Op1
Multiple = Op1;
return true;
}
}
Value *Mul1 = nullptr;
if (ComputeMultiple(Op1, Base, Mul1, LookThroughSExt, Depth+1)) {
if (Constant *Op0C = dyn_cast<Constant>(Op0))
if (Constant *MulC = dyn_cast<Constant>(Mul1)) {
if (Op0C->getType()->getPrimitiveSizeInBits() <
MulC->getType()->getPrimitiveSizeInBits())
Op0C = ConstantExpr::getZExt(Op0C, MulC->getType());
if (Op0C->getType()->getPrimitiveSizeInBits() >
MulC->getType()->getPrimitiveSizeInBits())
MulC = ConstantExpr::getZExt(MulC, Op0C->getType());
// V == Base * (Mul1 * Op0), so return (Mul1 * Op0)
Multiple = ConstantExpr::getMul(MulC, Op0C);
return true;
}
if (ConstantInt *Mul1CI = dyn_cast<ConstantInt>(Mul1))
if (Mul1CI->getValue() == 1) {
// V == Base * Op0, so return Op0
Multiple = Op0;
return true;
}
}
}
}
// We could not determine if V is a multiple of Base.
return false;
}
Intrinsic::ID llvm::getIntrinsicForCallSite(ImmutableCallSite ICS,
const TargetLibraryInfo *TLI) {
const Function *F = ICS.getCalledFunction();
if (!F)
return Intrinsic::not_intrinsic;
if (F->isIntrinsic())
return F->getIntrinsicID();
if (!TLI)
return Intrinsic::not_intrinsic;
LibFunc Func;
// We're going to make assumptions on the semantics of the functions, check
// that the target knows that it's available in this environment and it does
// not have local linkage.
if (!F || F->hasLocalLinkage() || !TLI->getLibFunc(*F, Func))
return Intrinsic::not_intrinsic;
if (!ICS.onlyReadsMemory())
return Intrinsic::not_intrinsic;
// Otherwise check if we have a call to a function that can be turned into a
// vector intrinsic.
switch (Func) {
default:
break;
case LibFunc_sin:
case LibFunc_sinf:
case LibFunc_sinl:
return Intrinsic::sin;
case LibFunc_cos:
case LibFunc_cosf:
case LibFunc_cosl:
return Intrinsic::cos;
case LibFunc_exp:
case LibFunc_expf:
case LibFunc_expl:
return Intrinsic::exp;
case LibFunc_exp2:
case LibFunc_exp2f:
case LibFunc_exp2l:
return Intrinsic::exp2;
case LibFunc_log:
case LibFunc_logf:
case LibFunc_logl:
return Intrinsic::log;
case LibFunc_log10:
case LibFunc_log10f:
case LibFunc_log10l:
return Intrinsic::log10;
case LibFunc_log2:
case LibFunc_log2f:
case LibFunc_log2l:
return Intrinsic::log2;
case LibFunc_fabs:
case LibFunc_fabsf:
case LibFunc_fabsl:
return Intrinsic::fabs;
case LibFunc_fmin:
case LibFunc_fminf:
case LibFunc_fminl:
return Intrinsic::minnum;
case LibFunc_fmax:
case LibFunc_fmaxf:
case LibFunc_fmaxl:
return Intrinsic::maxnum;
case LibFunc_copysign:
case LibFunc_copysignf:
case LibFunc_copysignl:
return Intrinsic::copysign;
case LibFunc_floor:
case LibFunc_floorf:
case LibFunc_floorl:
return Intrinsic::floor;
case LibFunc_ceil:
case LibFunc_ceilf:
case LibFunc_ceill:
return Intrinsic::ceil;
case LibFunc_trunc:
case LibFunc_truncf:
case LibFunc_truncl:
return Intrinsic::trunc;
case LibFunc_rint:
case LibFunc_rintf:
case LibFunc_rintl:
return Intrinsic::rint;
case LibFunc_nearbyint:
case LibFunc_nearbyintf:
case LibFunc_nearbyintl:
return Intrinsic::nearbyint;
case LibFunc_round:
case LibFunc_roundf:
case LibFunc_roundl:
return Intrinsic::round;
case LibFunc_pow:
case LibFunc_powf:
case LibFunc_powl:
return Intrinsic::pow;
case LibFunc_sqrt:
case LibFunc_sqrtf:
case LibFunc_sqrtl:
if (ICS->hasNoNaNs())
return Intrinsic::sqrt;
return Intrinsic::not_intrinsic;
}
return Intrinsic::not_intrinsic;
}
/// Return true if we can prove that the specified FP value is never equal to
/// -0.0.
///
/// NOTE: this function will need to be revisited when we support non-default
/// rounding modes!
///
bool llvm::CannotBeNegativeZero(const Value *V, const TargetLibraryInfo *TLI,
unsigned Depth) {
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
return !CFP->getValueAPF().isNegZero();
if (Depth == MaxDepth)
return false; // Limit search depth.
const Operator *I = dyn_cast<Operator>(V);
if (!I) return false;
// Check if the nsz fast-math flag is set
if (const FPMathOperator *FPO = dyn_cast<FPMathOperator>(I))
if (FPO->hasNoSignedZeros())
return true;
// (add x, 0.0) is guaranteed to return +0.0, not -0.0.
if (I->getOpcode() == Instruction::FAdd)
if (ConstantFP *CFP = dyn_cast<ConstantFP>(I->getOperand(1)))
if (CFP->isNullValue())
return true;
// sitofp and uitofp turn into +0.0 for zero.
if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
return true;
if (const CallInst *CI = dyn_cast<CallInst>(I)) {
Intrinsic::ID IID = getIntrinsicForCallSite(CI, TLI);
switch (IID) {
default:
break;
// sqrt(-0.0) = -0.0, no other negative results are possible.
case Intrinsic::sqrt:
return CannotBeNegativeZero(CI->getArgOperand(0), TLI, Depth + 1);
// fabs(x) != -0.0
case Intrinsic::fabs:
return true;
}
}
return false;
}
/// If \p SignBitOnly is true, test for a known 0 sign bit rather than a
/// standard ordered compare. e.g. make -0.0 olt 0.0 be true because of the sign
/// bit despite comparing equal.
static bool cannotBeOrderedLessThanZeroImpl(const Value *V,
const TargetLibraryInfo *TLI,
bool SignBitOnly,
unsigned Depth) {
// TODO: This function does not do the right thing when SignBitOnly is true
// and we're lowering to a hypothetical IEEE 754-compliant-but-evil platform
// which flips the sign bits of NaNs. See
// https://llvm.org/bugs/show_bug.cgi?id=31702.
if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
return !CFP->getValueAPF().isNegative() ||
(!SignBitOnly && CFP->getValueAPF().isZero());
}
if (Depth == MaxDepth)
return false; // Limit search depth.
const Operator *I = dyn_cast<Operator>(V);
if (!I)
return false;
switch (I->getOpcode()) {
default:
break;
// Unsigned integers are always nonnegative.
case Instruction::UIToFP:
return true;
case Instruction::FMul:
// x*x is always non-negative or a NaN.
if (I->getOperand(0) == I->getOperand(1) &&
(!SignBitOnly || cast<FPMathOperator>(I)->hasNoNaNs()))
return true;
LLVM_FALLTHROUGH;
case Instruction::FAdd:
case Instruction::FDiv:
case Instruction::FRem:
return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
Depth + 1) &&
cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
Depth + 1);
case Instruction::Select:
return cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
Depth + 1) &&
cannotBeOrderedLessThanZeroImpl(I->getOperand(2), TLI, SignBitOnly,
Depth + 1);
case Instruction::FPExt:
case Instruction::FPTrunc:
// Widening/narrowing never change sign.
return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
Depth + 1);
case Instruction::Call:
const auto *CI = cast<CallInst>(I);
Intrinsic::ID IID = getIntrinsicForCallSite(CI, TLI);
switch (IID) {
default:
break;
case Intrinsic::maxnum:
return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
Depth + 1) ||
cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
Depth + 1);
case Intrinsic::minnum:
return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
Depth + 1) &&
cannotBeOrderedLessThanZeroImpl(I->getOperand(1), TLI, SignBitOnly,
Depth + 1);
case Intrinsic::exp:
case Intrinsic::exp2:
case Intrinsic::fabs:
return true;
case Intrinsic::sqrt:
// sqrt(x) is always >= -0 or NaN. Moreover, sqrt(x) == -0 iff x == -0.
if (!SignBitOnly)
return true;
return CI->hasNoNaNs() && (CI->hasNoSignedZeros() ||
CannotBeNegativeZero(CI->getOperand(0), TLI));
case Intrinsic::powi:
if (ConstantInt *Exponent = dyn_cast<ConstantInt>(I->getOperand(1))) {
// powi(x,n) is non-negative if n is even.
if (Exponent->getBitWidth() <= 64 && Exponent->getSExtValue() % 2u == 0)
return true;
}
// TODO: This is not correct. Given that exp is an integer, here are the
// ways that pow can return a negative value:
//
// pow(x, exp) --> negative if exp is odd and x is negative.
// pow(-0, exp) --> -inf if exp is negative odd.
// pow(-0, exp) --> -0 if exp is positive odd.
// pow(-inf, exp) --> -0 if exp is negative odd.
// pow(-inf, exp) --> -inf if exp is positive odd.
//
// Therefore, if !SignBitOnly, we can return true if x >= +0 or x is NaN,
// but we must return false if x == -0. Unfortunately we do not currently
// have a way of expressing this constraint. See details in
// https://llvm.org/bugs/show_bug.cgi?id=31702.
return cannotBeOrderedLessThanZeroImpl(I->getOperand(0), TLI, SignBitOnly,
Depth + 1);
case Intrinsic::fma:
case Intrinsic::fmuladd:
// x*x+y is non-negative if y is non-negative.
return I->getOperand(0) == I->getOperand(1) &&
(!SignBitOnly || cast<FPMathOperator>(I)->hasNoNaNs()) &&
cannotBeOrderedLessThanZeroImpl(I->getOperand(2), TLI, SignBitOnly,
Depth + 1);
}
break;
}
return false;
}
bool llvm::CannotBeOrderedLessThanZero(const Value *V,
const TargetLibraryInfo *TLI) {
return cannotBeOrderedLessThanZeroImpl(V, TLI, false, 0);
}
bool llvm::SignBitMustBeZero(const Value *V, const TargetLibraryInfo *TLI) {
return cannotBeOrderedLessThanZeroImpl(V, TLI, true, 0);
}
/// If the specified value can be set by repeating the same byte in memory,
/// return the i8 value that it is represented with. This is
/// true for all i8 values obviously, but is also true for i32 0, i32 -1,
/// i16 0xF0F0, double 0.0 etc. If the value can't be handled with a repeated
/// byte store (e.g. i16 0x1234), return null.
Value *llvm::isBytewiseValue(Value *V) {
// All byte-wide stores are splatable, even of arbitrary variables.
if (V->getType()->isIntegerTy(8)) return V;
// Handle 'null' ConstantArrayZero etc.
if (Constant *C = dyn_cast<Constant>(V))
if (C->isNullValue())
return Constant::getNullValue(Type::getInt8Ty(V->getContext()));
// Constant float and double values can be handled as integer values if the
// corresponding integer value is "byteable". An important case is 0.0.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
if (CFP->getType()->isFloatTy())
V = ConstantExpr::getBitCast(CFP, Type::getInt32Ty(V->getContext()));
if (CFP->getType()->isDoubleTy())
V = ConstantExpr::getBitCast(CFP, Type::getInt64Ty(V->getContext()));
// Don't handle long double formats, which have strange constraints.
}
// We can handle constant integers that are multiple of 8 bits.
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
if (CI->getBitWidth() % 8 == 0) {
assert(CI->getBitWidth() > 8 && "8 bits should be handled above!");
if (!CI->getValue().isSplat(8))
return nullptr;
return ConstantInt::get(V->getContext(), CI->getValue().trunc(8));
}
}
// A ConstantDataArray/Vector is splatable if all its members are equal and
// also splatable.
if (ConstantDataSequential *CA = dyn_cast<ConstantDataSequential>(V)) {
Value *Elt = CA->getElementAsConstant(0);
Value *Val = isBytewiseValue(Elt);
if (!Val)
return nullptr;
for (unsigned I = 1, E = CA->getNumElements(); I != E; ++I)
if (CA->getElementAsConstant(I) != Elt)
return nullptr;
return Val;
}
// Conceptually, we could handle things like:
// %a = zext i8 %X to i16
// %b = shl i16 %a, 8
// %c = or i16 %a, %b
// but until there is an example that actually needs this, it doesn't seem
// worth worrying about.
return nullptr;
}
// This is the recursive version of BuildSubAggregate. It takes a few different
// arguments. Idxs is the index within the nested struct From that we are
// looking at now (which is of type IndexedType). IdxSkip is the number of
// indices from Idxs that should be left out when inserting into the resulting
// struct. To is the result struct built so far, new insertvalue instructions
// build on that.
static Value *BuildSubAggregate(Value *From, Value* To, Type *IndexedType,
SmallVectorImpl<unsigned> &Idxs,
unsigned IdxSkip,
Instruction *InsertBefore) {
llvm::StructType *STy = dyn_cast<llvm::StructType>(IndexedType);
if (STy) {
// Save the original To argument so we can modify it
Value *OrigTo = To;
// General case, the type indexed by Idxs is a struct
for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
// Process each struct element recursively
Idxs.push_back(i);
Value *PrevTo = To;
To = BuildSubAggregate(From, To, STy->getElementType(i), Idxs, IdxSkip,
InsertBefore);
Idxs.pop_back();
if (!To) {
// Couldn't find any inserted value for this index? Cleanup
while (PrevTo != OrigTo) {
InsertValueInst* Del = cast<InsertValueInst>(PrevTo);
PrevTo = Del->getAggregateOperand();
Del->eraseFromParent();
}
// Stop processing elements
break;
}
}
// If we successfully found a value for each of our subaggregates
if (To)
return To;
}
// Base case, the type indexed by SourceIdxs is not a struct, or not all of
// the struct's elements had a value that was inserted directly. In the latter
// case, perhaps we can't determine each of the subelements individually, but
// we might be able to find the complete struct somewhere.
// Find the value that is at that particular spot
Value *V = FindInsertedValue(From, Idxs);
if (!V)
return nullptr;
// Insert the value in the new (sub) aggregrate
return llvm::InsertValueInst::Create(To, V, makeArrayRef(Idxs).slice(IdxSkip),
"tmp", InsertBefore);
}
// This helper takes a nested struct and extracts a part of it (which is again a
// struct) into a new value. For example, given the struct:
// { a, { b, { c, d }, e } }
// and the indices "1, 1" this returns
// { c, d }.
//
// It does this by inserting an insertvalue for each element in the resulting
// struct, as opposed to just inserting a single struct. This will only work if
// each of the elements of the substruct are known (ie, inserted into From by an
// insertvalue instruction somewhere).
//
// All inserted insertvalue instructions are inserted before InsertBefore
static Value *BuildSubAggregate(Value *From, ArrayRef<unsigned> idx_range,
Instruction *InsertBefore) {
assert(InsertBefore && "Must have someplace to insert!");
Type *IndexedType = ExtractValueInst::getIndexedType(From->getType(),
idx_range);
Value *To = UndefValue::get(IndexedType);
SmallVector<unsigned, 10> Idxs(idx_range.begin(), idx_range.end());
unsigned IdxSkip = Idxs.size();
return BuildSubAggregate(From, To, IndexedType, Idxs, IdxSkip, InsertBefore);
}
/// Given an aggregrate and an sequence of indices, see if
/// the scalar value indexed is already around as a register, for example if it
/// were inserted directly into the aggregrate.
///
/// If InsertBefore is not null, this function will duplicate (modified)
/// insertvalues when a part of a nested struct is extracted.
Value *llvm::FindInsertedValue(Value *V, ArrayRef<unsigned> idx_range,
Instruction *InsertBefore) {
// Nothing to index? Just return V then (this is useful at the end of our
// recursion).
if (idx_range.empty())
return V;
// We have indices, so V should have an indexable type.
assert((V->getType()->isStructTy() || V->getType()->isArrayTy()) &&
"Not looking at a struct or array?");
assert(ExtractValueInst::getIndexedType(V->getType(), idx_range) &&
"Invalid indices for type?");
if (Constant *C = dyn_cast<Constant>(V)) {
C = C->getAggregateElement(idx_range[0]);
if (!C) return nullptr;
return FindInsertedValue(C, idx_range.slice(1), InsertBefore);
}
if (InsertValueInst *I = dyn_cast<InsertValueInst>(V)) {
// Loop the indices for the insertvalue instruction in parallel with the
// requested indices
const unsigned *req_idx = idx_range.begin();
for (const unsigned *i = I->idx_begin(), *e = I->idx_end();
i != e; ++i, ++req_idx) {
if (req_idx == idx_range.end()) {
// We can't handle this without inserting insertvalues
if (!InsertBefore)
return nullptr;
// The requested index identifies a part of a nested aggregate. Handle
// this specially. For example,
// %A = insertvalue { i32, {i32, i32 } } undef, i32 10, 1, 0
// %B = insertvalue { i32, {i32, i32 } } %A, i32 11, 1, 1
// %C = extractvalue {i32, { i32, i32 } } %B, 1
// This can be changed into
// %A = insertvalue {i32, i32 } undef, i32 10, 0
// %C = insertvalue {i32, i32 } %A, i32 11, 1
// which allows the unused 0,0 element from the nested struct to be
// removed.
return BuildSubAggregate(V, makeArrayRef(idx_range.begin(), req_idx),
InsertBefore);
}
// This insert value inserts something else than what we are looking for.
// See if the (aggregate) value inserted into has the value we are
// looking for, then.
if (*req_idx != *i)
return FindInsertedValue(I->getAggregateOperand(), idx_range,
InsertBefore);
}
// If we end up here, the indices of the insertvalue match with those
// requested (though possibly only partially). Now we recursively look at
// the inserted value, passing any remaining indices.
return FindInsertedValue(I->getInsertedValueOperand(),
makeArrayRef(req_idx, idx_range.end()),
InsertBefore);
}
if (ExtractValueInst *I = dyn_cast<ExtractValueInst>(V)) {
// If we're extracting a value from an aggregate that was extracted from
// something else, we can extract from that something else directly instead.
// However, we will need to chain I's indices with the requested indices.
// Calculate the number of indices required
unsigned size = I->getNumIndices() + idx_range.size();
// Allocate some space to put the new indices in
SmallVector<unsigned, 5> Idxs;
Idxs.reserve(size);
// Add indices from the extract value instruction
Idxs.append(I->idx_begin(), I->idx_end());
// Add requested indices
Idxs.append(idx_range.begin(), idx_range.end());
assert(Idxs.size() == size
&& "Number of indices added not correct?");
return FindInsertedValue(I->getAggregateOperand(), Idxs, InsertBefore);
}
// Otherwise, we don't know (such as, extracting from a function return value
// or load instruction)
return nullptr;
}
/// Analyze the specified pointer to see if it can be expressed as a base
/// pointer plus a constant offset. Return the base and offset to the caller.
Value *llvm::GetPointerBaseWithConstantOffset(Value *Ptr, int64_t &Offset,
const DataLayout &DL) {
unsigned BitWidth = DL.getPointerTypeSizeInBits(Ptr->getType());
APInt ByteOffset(BitWidth, 0);
// We walk up the defs but use a visited set to handle unreachable code. In
// that case, we stop after accumulating the cycle once (not that it
// matters).
SmallPtrSet<Value *, 16> Visited;
while (Visited.insert(Ptr).second) {
if (Ptr->getType()->isVectorTy())
break;
if (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
// If one of the values we have visited is an addrspacecast, then
// the pointer type of this GEP may be different from the type
// of the Ptr parameter which was passed to this function. This
// means when we construct GEPOffset, we need to use the size
// of GEP's pointer type rather than the size of the original
// pointer type.
APInt GEPOffset(DL.getPointerTypeSizeInBits(Ptr->getType()), 0);
if (!GEP->accumulateConstantOffset(DL, GEPOffset))
break;
ByteOffset += GEPOffset.getSExtValue();
Ptr = GEP->getPointerOperand();
} else if (Operator::getOpcode(Ptr) == Instruction::BitCast ||
Operator::getOpcode(Ptr) == Instruction::AddrSpaceCast) {
Ptr = cast<Operator>(Ptr)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
if (GA->isInterposable())
break;
Ptr = GA->getAliasee();
} else {
break;
}
}
Offset = ByteOffset.getSExtValue();
return Ptr;
}
bool llvm::isGEPBasedOnPointerToString(const GEPOperator *GEP) {
// Make sure the GEP has exactly three arguments.
if (GEP->getNumOperands() != 3)
return false;
// Make sure the index-ee is a pointer to array of i8.
ArrayType *AT = dyn_cast<ArrayType>(GEP->getSourceElementType());
if (!AT || !AT->getElementType()->isIntegerTy(8))
return false;
// Check to make sure that the first operand of the GEP is an integer and
// has value 0 so that we are sure we're indexing into the initializer.
const ConstantInt *FirstIdx = dyn_cast<ConstantInt>(GEP->getOperand(1));
if (!FirstIdx || !FirstIdx->isZero())
return false;
return true;
}
/// This function computes the length of a null-terminated C string pointed to
/// by V. If successful, it returns true and returns the string in Str.
/// If unsuccessful, it returns false.
bool llvm::getConstantStringInfo(const Value *V, StringRef &Str,
uint64_t Offset, bool TrimAtNul) {
assert(V);
// Look through bitcast instructions and geps.
V = V->stripPointerCasts();
// If the value is a GEP instruction or constant expression, treat it as an
// offset.
if (const GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
// The GEP operator should be based on a pointer to string constant, and is
// indexing into the string constant.
if (!isGEPBasedOnPointerToString(GEP))
return false;
// If the second index isn't a ConstantInt, then this is a variable index
// into the array. If this occurs, we can't say anything meaningful about
// the string.
uint64_t StartIdx = 0;
if (const ConstantInt *CI = dyn_cast<ConstantInt>(GEP->getOperand(2)))
StartIdx = CI->getZExtValue();
else
return false;
return getConstantStringInfo(GEP->getOperand(0), Str, StartIdx + Offset,
TrimAtNul);
}
// The GEP instruction, constant or instruction, must reference a global
// variable that is a constant and is initialized. The referenced constant
// initializer is the array that we'll use for optimization.
const GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
if (!GV || !GV->isConstant() || !GV->hasDefinitiveInitializer())
return false;
// Handle the all-zeros case.
if (GV->getInitializer()->isNullValue()) {
// This is a degenerate case. The initializer is constant zero so the
// length of the string must be zero.
Str = "";
return true;
}
// This must be a ConstantDataArray.
const auto *Array = dyn_cast<ConstantDataArray>(GV->getInitializer());
if (!Array || !Array->isString())
return false;
// Get the number of elements in the array.
uint64_t NumElts = Array->getType()->getArrayNumElements();
// Start out with the entire array in the StringRef.
Str = Array->getAsString();
if (Offset > NumElts)
return false;
// Skip over 'offset' bytes.
Str = Str.substr(Offset);
if (TrimAtNul) {
// Trim off the \0 and anything after it. If the array is not nul
// terminated, we just return the whole end of string. The client may know
// some other way that the string is length-bound.
Str = Str.substr(0, Str.find('\0'));
}
return true;
}
// These next two are very similar to the above, but also look through PHI
// nodes.
// TODO: See if we can integrate these two together.
/// If we can compute the length of the string pointed to by
/// the specified pointer, return 'len+1'. If we can't, return 0.
static uint64_t GetStringLengthH(const Value *V,
SmallPtrSetImpl<const PHINode*> &PHIs) {
// Look through noop bitcast instructions.
V = V->stripPointerCasts();
// If this is a PHI node, there are two cases: either we have already seen it
// or we haven't.
if (const PHINode *PN = dyn_cast<PHINode>(V)) {
if (!PHIs.insert(PN).second)
return ~0ULL; // already in the set.
// If it was new, see if all the input strings are the same length.
uint64_t LenSoFar = ~0ULL;
for (Value *IncValue : PN->incoming_values()) {
uint64_t Len = GetStringLengthH(IncValue, PHIs);
if (Len == 0) return 0; // Unknown length -> unknown.
if (Len == ~0ULL) continue;
if (Len != LenSoFar && LenSoFar != ~0ULL)
return 0; // Disagree -> unknown.
LenSoFar = Len;
}
// Success, all agree.
return LenSoFar;
}
// strlen(select(c,x,y)) -> strlen(x) ^ strlen(y)
if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
uint64_t Len1 = GetStringLengthH(SI->getTrueValue(), PHIs);
if (Len1 == 0) return 0;
uint64_t Len2 = GetStringLengthH(SI->getFalseValue(), PHIs);
if (Len2 == 0) return 0;
if (Len1 == ~0ULL) return Len2;
if (Len2 == ~0ULL) return Len1;
if (Len1 != Len2) return 0;
return Len1;
}
// Otherwise, see if we can read the string.
StringRef StrData;
if (!getConstantStringInfo(V, StrData))
return 0;
return StrData.size()+1;
}
/// If we can compute the length of the string pointed to by
/// the specified pointer, return 'len+1'. If we can't, return 0.
uint64_t llvm::GetStringLength(const Value *V) {
if (!V->getType()->isPointerTy()) return 0;
SmallPtrSet<const PHINode*, 32> PHIs;
uint64_t Len = GetStringLengthH(V, PHIs);
// If Len is ~0ULL, we had an infinite phi cycle: this is dead code, so return
// an empty string as a length.
return Len == ~0ULL ? 1 : Len;
}
/// \brief \p PN defines a loop-variant pointer to an object. Check if the
/// previous iteration of the loop was referring to the same object as \p PN.
static bool isSameUnderlyingObjectInLoop(const PHINode *PN,
const LoopInfo *LI) {
// Find the loop-defined value.
Loop *L = LI->getLoopFor(PN->getParent());
if (PN->getNumIncomingValues() != 2)
return true;
// Find the value from previous iteration.
auto *PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(0));
if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L)
PrevValue = dyn_cast<Instruction>(PN->getIncomingValue(1));
if (!PrevValue || LI->getLoopFor(PrevValue->getParent()) != L)
return true;
// If a new pointer is loaded in the loop, the pointer references a different
// object in every iteration. E.g.:
// for (i)
// int *p = a[i];
// ...
if (auto *Load = dyn_cast<LoadInst>(PrevValue))
if (!L->isLoopInvariant(Load->getPointerOperand()))
return false;
return true;
}
Value *llvm::GetUnderlyingObject(Value *V, const DataLayout &DL,
unsigned MaxLookup) {
if (!V->getType()->isPointerTy())
return V;
for (unsigned Count = 0; MaxLookup == 0 || Count < MaxLookup; ++Count) {
if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
V = GEP->getPointerOperand();
} else if (Operator::getOpcode(V) == Instruction::BitCast ||
Operator::getOpcode(V) == Instruction::AddrSpaceCast) {
V = cast<Operator>(V)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
if (GA->isInterposable())
return V;
V = GA->getAliasee();
} else {
if (auto CS = CallSite(V))
if (Value *RV = CS.getReturnedArgOperand()) {
V = RV;
continue;
}
// See if InstructionSimplify knows any relevant tricks.
if (Instruction *I = dyn_cast<Instruction>(V))
// TODO: Acquire a DominatorTree and AssumptionCache and use them.
if (Value *Simplified = SimplifyInstruction(I, DL, nullptr)) {
V = Simplified;
continue;
}
return V;
}
assert(V->getType()->isPointerTy() && "Unexpected operand type!");
}
return V;
}
void llvm::GetUnderlyingObjects(Value *V, SmallVectorImpl<Value *> &Objects,
const DataLayout &DL, LoopInfo *LI,
unsigned MaxLookup) {
SmallPtrSet<Value *, 4> Visited;
SmallVector<Value *, 4> Worklist;
Worklist.push_back(V);
do {
Value *P = Worklist.pop_back_val();
P = GetUnderlyingObject(P, DL, MaxLookup);
if (!Visited.insert(P).second)
continue;
if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
Worklist.push_back(SI->getTrueValue());
Worklist.push_back(SI->getFalseValue());
continue;
}
if (PHINode *PN = dyn_cast<PHINode>(P)) {
// If this PHI changes the underlying object in every iteration of the
// loop, don't look through it. Consider:
// int **A;
// for (i) {
// Prev = Curr; // Prev = PHI (Prev_0, Curr)
// Curr = A[i];
// *Prev, *Curr;
//
// Prev is tracking Curr one iteration behind so they refer to different
// underlying objects.
if (!LI || !LI->isLoopHeader(PN->getParent()) ||
isSameUnderlyingObjectInLoop(PN, LI))
for (Value *IncValue : PN->incoming_values())
Worklist.push_back(IncValue);
continue;
}
Objects.push_back(P);
} while (!Worklist.empty());
}
/// Return true if the only users of this pointer are lifetime markers.
bool llvm::onlyUsedByLifetimeMarkers(const Value *V) {
for (const User *U : V->users()) {
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(U);
if (!II) return false;
if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
II->getIntrinsicID() != Intrinsic::lifetime_end)
return false;
}
return true;
}
bool llvm::isSafeToSpeculativelyExecute(const Value *V,
const Instruction *CtxI,
const DominatorTree *DT) {
const Operator *Inst = dyn_cast<Operator>(V);
if (!Inst)
return false;
for (unsigned i = 0, e = Inst->getNumOperands(); i != e; ++i)
if (Constant *C = dyn_cast<Constant>(Inst->getOperand(i)))
if (C->canTrap())
return false;
switch (Inst->getOpcode()) {
default:
return true;
case Instruction::UDiv:
case Instruction::URem: {
// x / y is undefined if y == 0.
const APInt *V;
if (match(Inst->getOperand(1), m_APInt(V)))
return *V != 0;
return false;
}
case Instruction::SDiv:
case Instruction::SRem: {
// x / y is undefined if y == 0 or x == INT_MIN and y == -1
const APInt *Numerator, *Denominator;
if (!match(Inst->getOperand(1), m_APInt(Denominator)))
return false;
// We cannot hoist this division if the denominator is 0.
if (*Denominator == 0)
return false;
// It's safe to hoist if the denominator is not 0 or -1.
if (*Denominator != -1)
return true;
// At this point we know that the denominator is -1. It is safe to hoist as
// long we know that the numerator is not INT_MIN.
if (match(Inst->getOperand(0), m_APInt(Numerator)))
return !Numerator->isMinSignedValue();
// The numerator *might* be MinSignedValue.
return false;
}
case Instruction::Load: {
const LoadInst *LI = cast<LoadInst>(Inst);
if (!LI->isUnordered() ||
// Speculative load may create a race that did not exist in the source.
LI->getFunction()->hasFnAttribute(Attribute::SanitizeThread) ||
// Speculative load may load data from dirty regions.
LI->getFunction()->hasFnAttribute(Attribute::SanitizeAddress))
return false;
const DataLayout &DL = LI->getModule()->getDataLayout();
return isDereferenceableAndAlignedPointer(LI->getPointerOperand(),
LI->getAlignment(), DL, CtxI, DT);
}
case Instruction::Call: {
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
switch (II->getIntrinsicID()) {
// These synthetic intrinsics have no side-effects and just mark
// information about their operands.
// FIXME: There are other no-op synthetic instructions that potentially
// should be considered at least *safe* to speculate...
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
return true;
case Intrinsic::bitreverse:
case Intrinsic::bswap:
case Intrinsic::ctlz:
case Intrinsic::ctpop:
case Intrinsic::cttz:
case Intrinsic::objectsize:
case Intrinsic::sadd_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::umul_with_overflow:
case Intrinsic::usub_with_overflow:
return true;
// These intrinsics are defined to have the same behavior as libm
// functions except for setting errno.
case Intrinsic::sqrt:
case Intrinsic::fma:
case Intrinsic::fmuladd:
return true;
// These intrinsics are defined to have the same behavior as libm
// functions, and the corresponding libm functions never set errno.
case Intrinsic::trunc:
case Intrinsic::copysign:
case Intrinsic::fabs:
case Intrinsic::minnum:
case Intrinsic::maxnum:
return true;
// These intrinsics are defined to have the same behavior as libm
// functions, which never overflow when operating on the IEEE754 types
// that we support, and never set errno otherwise.
case Intrinsic::ceil:
case Intrinsic::floor:
case Intrinsic::nearbyint:
case Intrinsic::rint:
case Intrinsic::round:
return true;
// These intrinsics do not correspond to any libm function, and
// do not set errno.
case Intrinsic::powi:
return true;
// TODO: are convert_{from,to}_fp16 safe?
// TODO: can we list target-specific intrinsics here?
default: break;
}
}
return false; // The called function could have undefined behavior or
// side-effects, even if marked readnone nounwind.
}
case Instruction::VAArg:
case Instruction::Alloca:
case Instruction::Invoke:
case Instruction::PHI:
case Instruction::Store:
case Instruction::Ret:
case Instruction::Br:
case Instruction::IndirectBr:
case Instruction::Switch:
case Instruction::Unreachable:
case Instruction::Fence:
case Instruction::AtomicRMW:
case Instruction::AtomicCmpXchg:
case Instruction::LandingPad:
case Instruction::Resume:
case Instruction::CatchSwitch:
case Instruction::CatchPad:
case Instruction::CatchRet:
case Instruction::CleanupPad:
case Instruction::CleanupRet:
return false; // Misc instructions which have effects
}
}
bool llvm::mayBeMemoryDependent(const Instruction &I) {
return I.mayReadOrWriteMemory() || !isSafeToSpeculativelyExecute(&I);
}
/// Return true if we know that the specified value is never null.
bool llvm::isKnownNonNull(const Value *V) {
assert(V->getType()->isPointerTy() && "V must be pointer type");
// Alloca never returns null, malloc might.
if (isa<AllocaInst>(V)) return true;
// A byval, inalloca, or nonnull argument is never null.
if (const Argument *A = dyn_cast<Argument>(V))
return A->hasByValOrInAllocaAttr() || A->hasNonNullAttr();
// A global variable in address space 0 is non null unless extern weak
// or an absolute symbol reference. Other address spaces may have null as a
// valid address for a global, so we can't assume anything.
if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
return !GV->isAbsoluteSymbolRef() && !GV->hasExternalWeakLinkage() &&
GV->getType()->getAddressSpace() == 0;
// A Load tagged with nonnull metadata is never null.
if (const LoadInst *LI = dyn_cast<LoadInst>(V))
return LI->getMetadata(LLVMContext::MD_nonnull);
if (auto CS = ImmutableCallSite(V))
if (CS.isReturnNonNull())
return true;
return false;
}
static bool isKnownNonNullFromDominatingCondition(const Value *V,
const Instruction *CtxI,
const DominatorTree *DT) {
assert(V->getType()->isPointerTy() && "V must be pointer type");
assert(!isa<ConstantData>(V) && "Did not expect ConstantPointerNull");
assert(CtxI && "Context instruction required for analysis");
assert(DT && "Dominator tree required for analysis");
unsigned NumUsesExplored = 0;
for (auto *U : V->users()) {
// Avoid massive lists
if (NumUsesExplored >= DomConditionsMaxUses)
break;
NumUsesExplored++;
// If the value is used as an argument to a call or invoke, then argument
// attributes may provide an answer about null-ness.
if (auto CS = ImmutableCallSite(U))
if (auto *CalledFunc = CS.getCalledFunction())
for (const Argument &Arg : CalledFunc->args())
if (CS.getArgOperand(Arg.getArgNo()) == V &&
Arg.hasNonNullAttr() && DT->dominates(CS.getInstruction(), CtxI))
return true;
// Consider only compare instructions uniquely controlling a branch
CmpInst::Predicate Pred;
if (!match(const_cast<User *>(U),
m_c_ICmp(Pred, m_Specific(V), m_Zero())) ||
(Pred != ICmpInst::ICMP_EQ && Pred != ICmpInst::ICMP_NE))
continue;
for (auto *CmpU : U->users()) {
if (const BranchInst *BI = dyn_cast<BranchInst>(CmpU)) {
assert(BI->isConditional() && "uses a comparison!");
BasicBlock *NonNullSuccessor =
BI->getSuccessor(Pred == ICmpInst::ICMP_EQ ? 1 : 0);
BasicBlockEdge Edge(BI->getParent(), NonNullSuccessor);
if (Edge.isSingleEdge() && DT->dominates(Edge, CtxI->getParent()))
return true;
} else if (Pred == ICmpInst::ICMP_NE &&
match(CmpU, m_Intrinsic<Intrinsic::experimental_guard>()) &&
DT->dominates(cast<Instruction>(CmpU), CtxI)) {
return true;
}
}
}
return false;
}
bool llvm::isKnownNonNullAt(const Value *V, const Instruction *CtxI,
const DominatorTree *DT) {
if (isa<ConstantPointerNull>(V) || isa<UndefValue>(V))
return false;
if (isKnownNonNull(V))
return true;
if (!CtxI || !DT)
return false;
return ::isKnownNonNullFromDominatingCondition(V, CtxI, DT);
}
OverflowResult llvm::computeOverflowForUnsignedMul(const Value *LHS,
const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
// Multiplying n * m significant bits yields a result of n + m significant
// bits. If the total number of significant bits does not exceed the
// result bit width (minus 1), there is no overflow.
// This means if we have enough leading zero bits in the operands
// we can guarantee that the result does not overflow.
// Ref: "Hacker's Delight" by Henry Warren
unsigned BitWidth = LHS->getType()->getScalarSizeInBits();
APInt LHSKnownZero(BitWidth, 0);
APInt LHSKnownOne(BitWidth, 0);
APInt RHSKnownZero(BitWidth, 0);
APInt RHSKnownOne(BitWidth, 0);
computeKnownBits(LHS, LHSKnownZero, LHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
DT);
computeKnownBits(RHS, RHSKnownZero, RHSKnownOne, DL, /*Depth=*/0, AC, CxtI,
DT);
// Note that underestimating the number of zero bits gives a more
// conservative answer.
unsigned ZeroBits = LHSKnownZero.countLeadingOnes() +
RHSKnownZero.countLeadingOnes();
// First handle the easy case: if we have enough zero bits there's
// definitely no overflow.
if (ZeroBits >= BitWidth)
return OverflowResult::NeverOverflows;
// Get the largest possible values for each operand.
APInt LHSMax = ~LHSKnownZero;
APInt RHSMax = ~RHSKnownZero;
// We know the multiply operation doesn't overflow if the maximum values for
// each operand will not overflow after we multiply them together.
bool MaxOverflow;
LHSMax.umul_ov(RHSMax, MaxOverflow);
if (!MaxOverflow)
return OverflowResult::NeverOverflows;
// We know it always overflows if multiplying the smallest possible values for
// the operands also results in overflow.
bool MinOverflow;
LHSKnownOne.umul_ov(RHSKnownOne, MinOverflow);
if (MinOverflow)
return OverflowResult::AlwaysOverflows;
return OverflowResult::MayOverflow;
}
OverflowResult llvm::computeOverflowForUnsignedAdd(const Value *LHS,
const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
bool LHSKnownNonNegative, LHSKnownNegative;
ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
AC, CxtI, DT);
if (LHSKnownNonNegative || LHSKnownNegative) {
bool RHSKnownNonNegative, RHSKnownNegative;
ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
AC, CxtI, DT);
if (LHSKnownNegative && RHSKnownNegative) {
// The sign bit is set in both cases: this MUST overflow.
// Create a simple add instruction, and insert it into the struct.
return OverflowResult::AlwaysOverflows;
}
if (LHSKnownNonNegative && RHSKnownNonNegative) {
// The sign bit is clear in both cases: this CANNOT overflow.
// Create a simple add instruction, and insert it into the struct.
return OverflowResult::NeverOverflows;
}
}
return OverflowResult::MayOverflow;
}
static OverflowResult computeOverflowForSignedAdd(const Value *LHS,
const Value *RHS,
const AddOperator *Add,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
if (Add && Add->hasNoSignedWrap()) {
return OverflowResult::NeverOverflows;
}
bool LHSKnownNonNegative, LHSKnownNegative;
bool RHSKnownNonNegative, RHSKnownNegative;
ComputeSignBit(LHS, LHSKnownNonNegative, LHSKnownNegative, DL, /*Depth=*/0,
AC, CxtI, DT);
ComputeSignBit(RHS, RHSKnownNonNegative, RHSKnownNegative, DL, /*Depth=*/0,
AC, CxtI, DT);
if ((LHSKnownNonNegative && RHSKnownNegative) ||
(LHSKnownNegative && RHSKnownNonNegative)) {
// The sign bits are opposite: this CANNOT overflow.
return OverflowResult::NeverOverflows;
}
// The remaining code needs Add to be available. Early returns if not so.
if (!Add)
return OverflowResult::MayOverflow;
// If the sign of Add is the same as at least one of the operands, this add
// CANNOT overflow. This is particularly useful when the sum is
// @llvm.assume'ed non-negative rather than proved so from analyzing its
// operands.
bool LHSOrRHSKnownNonNegative =
(LHSKnownNonNegative || RHSKnownNonNegative);
bool LHSOrRHSKnownNegative = (LHSKnownNegative || RHSKnownNegative);
if (LHSOrRHSKnownNonNegative || LHSOrRHSKnownNegative) {
bool AddKnownNonNegative, AddKnownNegative;
ComputeSignBit(Add, AddKnownNonNegative, AddKnownNegative, DL,
/*Depth=*/0, AC, CxtI, DT);
if ((AddKnownNonNegative && LHSOrRHSKnownNonNegative) ||
(AddKnownNegative && LHSOrRHSKnownNegative)) {
return OverflowResult::NeverOverflows;
}
}
return OverflowResult::MayOverflow;
}
bool llvm::isOverflowIntrinsicNoWrap(const IntrinsicInst *II,
const DominatorTree &DT) {
#ifndef NDEBUG
auto IID = II->getIntrinsicID();
assert((IID == Intrinsic::sadd_with_overflow ||
IID == Intrinsic::uadd_with_overflow ||
IID == Intrinsic::ssub_with_overflow ||
IID == Intrinsic::usub_with_overflow ||
IID == Intrinsic::smul_with_overflow ||
IID == Intrinsic::umul_with_overflow) &&
"Not an overflow intrinsic!");
#endif
SmallVector<const BranchInst *, 2> GuardingBranches;
SmallVector<const ExtractValueInst *, 2> Results;
for (const User *U : II->users()) {
if (const auto *EVI = dyn_cast<ExtractValueInst>(U)) {
assert(EVI->getNumIndices() == 1 && "Obvious from CI's type");
if (EVI->getIndices()[0] == 0)
Results.push_back(EVI);
else {
assert(EVI->getIndices()[0] == 1 && "Obvious from CI's type");
for (const auto *U : EVI->users())
if (const auto *B = dyn_cast<BranchInst>(U)) {
assert(B->isConditional() && "How else is it using an i1?");
GuardingBranches.push_back(B);
}
}
} else {
// We are using the aggregate directly in a way we don't want to analyze
// here (storing it to a global, say).
return false;
}
}
auto AllUsesGuardedByBranch = [&](const BranchInst *BI) {
BasicBlockEdge NoWrapEdge(BI->getParent(), BI->getSuccessor(1));
if (!NoWrapEdge.isSingleEdge())
return false;
// Check if all users of the add are provably no-wrap.
for (const auto *Result : Results) {
// If the extractvalue itself is not executed on overflow, the we don't
// need to check each use separately, since domination is transitive.
if (DT.dominates(NoWrapEdge, Result->getParent()))
continue;
for (auto &RU : Result->uses())
if (!DT.dominates(NoWrapEdge, RU))
return false;
}
return true;
};
return any_of(GuardingBranches, AllUsesGuardedByBranch);
}
OverflowResult llvm::computeOverflowForSignedAdd(const AddOperator *Add,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
return ::computeOverflowForSignedAdd(Add->getOperand(0), Add->getOperand(1),
Add, DL, AC, CxtI, DT);
}
OverflowResult llvm::computeOverflowForSignedAdd(const Value *LHS,
const Value *RHS,
const DataLayout &DL,
AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
return ::computeOverflowForSignedAdd(LHS, RHS, nullptr, DL, AC, CxtI, DT);
}
bool llvm::isGuaranteedToTransferExecutionToSuccessor(const Instruction *I) {
// A memory operation returns normally if it isn't volatile. A volatile
// operation is allowed to trap.
//
// An atomic operation isn't guaranteed to return in a reasonable amount of
// time because it's possible for another thread to interfere with it for an
// arbitrary length of time, but programs aren't allowed to rely on that.
if (const LoadInst *LI = dyn_cast<LoadInst>(I))
return !LI->isVolatile();
if (const StoreInst *SI = dyn_cast<StoreInst>(I))
return !SI->isVolatile();
if (const AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(I))
return !CXI->isVolatile();
if (const AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(I))
return !RMWI->isVolatile();
if (const MemIntrinsic *MII = dyn_cast<MemIntrinsic>(I))
return !MII->isVolatile();
// If there is no successor, then execution can't transfer to it.
if (const auto *CRI = dyn_cast<CleanupReturnInst>(I))
return !CRI->unwindsToCaller();
if (const auto *CatchSwitch = dyn_cast<CatchSwitchInst>(I))
return !CatchSwitch->unwindsToCaller();
if (isa<ResumeInst>(I))
return false;
if (isa<ReturnInst>(I))
return false;
// Calls can throw, or contain an infinite loop, or kill the process.
if (auto CS = ImmutableCallSite(I)) {
// Call sites that throw have implicit non-local control flow.
if (!CS.doesNotThrow())
return false;
// Non-throwing call sites can loop infinitely, call exit/pthread_exit
// etc. and thus not return. However, LLVM already assumes that
//
// - Thread exiting actions are modeled as writes to memory invisible to
// the program.
//
// - Loops that don't have side effects (side effects are volatile/atomic
// stores and IO) always terminate (see http://llvm.org/PR965).
// Furthermore IO itself is also modeled as writes to memory invisible to
// the program.
//
// We rely on those assumptions here, and use the memory effects of the call
// target as a proxy for checking that it always returns.
// FIXME: This isn't aggressive enough; a call which only writes to a global
// is guaranteed to return.
return CS.onlyReadsMemory() || CS.onlyAccessesArgMemory() ||
match(I, m_Intrinsic<Intrinsic::assume>());
}
// Other instructions return normally.
return true;
}
bool llvm::isGuaranteedToExecuteForEveryIteration(const Instruction *I,
const Loop *L) {
// The loop header is guaranteed to be executed for every iteration.
//
// FIXME: Relax this constraint to cover all basic blocks that are
// guaranteed to be executed at every iteration.
if (I->getParent() != L->getHeader()) return false;
for (const Instruction &LI : *L->getHeader()) {
if (&LI == I) return true;
if (!isGuaranteedToTransferExecutionToSuccessor(&LI)) return false;
}
llvm_unreachable("Instruction not contained in its own parent basic block.");
}
bool llvm::propagatesFullPoison(const Instruction *I) {
switch (I->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Xor:
case Instruction::Trunc:
case Instruction::BitCast:
case Instruction::AddrSpaceCast:
case Instruction::Mul:
case Instruction::Shl:
case Instruction::GetElementPtr:
// These operations all propagate poison unconditionally. Note that poison
// is not any particular value, so xor or subtraction of poison with
// itself still yields poison, not zero.
return true;
case Instruction::AShr:
case Instruction::SExt:
// For these operations, one bit of the input is replicated across
// multiple output bits. A replicated poison bit is still poison.
return true;
case Instruction::ICmp:
// Comparing poison with any value yields poison. This is why, for
// instance, x s< (x +nsw 1) can be folded to true.
return true;
default:
return false;
}
}
const Value *llvm::getGuaranteedNonFullPoisonOp(const Instruction *I) {
switch (I->getOpcode()) {
case Instruction::Store:
return cast<StoreInst>(I)->getPointerOperand();
case Instruction::Load:
return cast<LoadInst>(I)->getPointerOperand();
case Instruction::AtomicCmpXchg:
return cast<AtomicCmpXchgInst>(I)->getPointerOperand();
case Instruction::AtomicRMW:
return cast<AtomicRMWInst>(I)->getPointerOperand();
case Instruction::UDiv:
case Instruction::SDiv:
case Instruction::URem:
case Instruction::SRem:
return I->getOperand(1);
default:
return nullptr;
}
}
bool llvm::isKnownNotFullPoison(const Instruction *PoisonI) {
// We currently only look for uses of poison values within the same basic
// block, as that makes it easier to guarantee that the uses will be
// executed given that PoisonI is executed.
//
// FIXME: Expand this to consider uses beyond the same basic block. To do
// this, look out for the distinction between post-dominance and strong
// post-dominance.
const BasicBlock *BB = PoisonI->getParent();
// Set of instructions that we have proved will yield poison if PoisonI
// does.
SmallSet<const Value *, 16> YieldsPoison;
SmallSet<const BasicBlock *, 4> Visited;
YieldsPoison.insert(PoisonI);
Visited.insert(PoisonI->getParent());
BasicBlock::const_iterator Begin = PoisonI->getIterator(), End = BB->end();
unsigned Iter = 0;
while (Iter++ < MaxDepth) {
for (auto &I : make_range(Begin, End)) {
if (&I != PoisonI) {
const Value *NotPoison = getGuaranteedNonFullPoisonOp(&I);
if (NotPoison != nullptr && YieldsPoison.count(NotPoison))
return true;
if (!isGuaranteedToTransferExecutionToSuccessor(&I))
return false;
}
// Mark poison that propagates from I through uses of I.
if (YieldsPoison.count(&I)) {
for (const User *User : I.users()) {
const Instruction *UserI = cast<Instruction>(User);
if (propagatesFullPoison(UserI))
YieldsPoison.insert(User);
}
}
}
if (auto *NextBB = BB->getSingleSuccessor()) {
if (Visited.insert(NextBB).second) {
BB = NextBB;
Begin = BB->getFirstNonPHI()->getIterator();
End = BB->end();
continue;
}
}
break;
};
return false;
}
static bool isKnownNonNaN(const Value *V, FastMathFlags FMF) {
if (FMF.noNaNs())
return true;
if (auto *C = dyn_cast<ConstantFP>(V))
return !C->isNaN();
return false;
}
static bool isKnownNonZero(const Value *V) {
if (auto *C = dyn_cast<ConstantFP>(V))
return !C->isZero();
return false;
}
/// Match non-obvious integer minimum and maximum sequences.
static SelectPatternResult matchMinMax(CmpInst::Predicate Pred,
Value *CmpLHS, Value *CmpRHS,
Value *TrueVal, Value *FalseVal,
Value *&LHS, Value *&RHS) {
// Assume success. If there's no match, callers should not use these anyway.
LHS = TrueVal;
RHS = FalseVal;
// Recognize variations of:
// CLAMP(v,l,h) ==> ((v) < (l) ? (l) : ((v) > (h) ? (h) : (v)))
const APInt *C1;
if (CmpRHS == TrueVal && match(CmpRHS, m_APInt(C1))) {
const APInt *C2;
// (X <s C1) ? C1 : SMIN(X, C2) ==> SMAX(SMIN(X, C2), C1)
if (match(FalseVal, m_SMin(m_Specific(CmpLHS), m_APInt(C2))) &&
C1->slt(*C2) && Pred == CmpInst::ICMP_SLT)
return {SPF_SMAX, SPNB_NA, false};
// (X >s C1) ? C1 : SMAX(X, C2) ==> SMIN(SMAX(X, C2), C1)
if (match(FalseVal, m_SMax(m_Specific(CmpLHS), m_APInt(C2))) &&
C1->sgt(*C2) && Pred == CmpInst::ICMP_SGT)
return {SPF_SMIN, SPNB_NA, false};
// (X <u C1) ? C1 : UMIN(X, C2) ==> UMAX(UMIN(X, C2), C1)
if (match(FalseVal, m_UMin(m_Specific(CmpLHS), m_APInt(C2))) &&
C1->ult(*C2) && Pred == CmpInst::ICMP_ULT)
return {SPF_UMAX, SPNB_NA, false};
// (X >u C1) ? C1 : UMAX(X, C2) ==> UMIN(UMAX(X, C2), C1)
if (match(FalseVal, m_UMax(m_Specific(CmpLHS), m_APInt(C2))) &&
C1->ugt(*C2) && Pred == CmpInst::ICMP_UGT)
return {SPF_UMIN, SPNB_NA, false};
}
if (Pred != CmpInst::ICMP_SGT && Pred != CmpInst::ICMP_SLT)
return {SPF_UNKNOWN, SPNB_NA, false};
// Z = X -nsw Y
// (X >s Y) ? 0 : Z ==> (Z >s 0) ? 0 : Z ==> SMIN(Z, 0)
// (X <s Y) ? 0 : Z ==> (Z <s 0) ? 0 : Z ==> SMAX(Z, 0)
if (match(TrueVal, m_Zero()) &&
match(FalseVal, m_NSWSub(m_Specific(CmpLHS), m_Specific(CmpRHS))))
return {Pred == CmpInst::ICMP_SGT ? SPF_SMIN : SPF_SMAX, SPNB_NA, false};
// Z = X -nsw Y
// (X >s Y) ? Z : 0 ==> (Z >s 0) ? Z : 0 ==> SMAX(Z, 0)
// (X <s Y) ? Z : 0 ==> (Z <s 0) ? Z : 0 ==> SMIN(Z, 0)
if (match(FalseVal, m_Zero()) &&
match(TrueVal, m_NSWSub(m_Specific(CmpLHS), m_Specific(CmpRHS))))
return {Pred == CmpInst::ICMP_SGT ? SPF_SMAX : SPF_SMIN, SPNB_NA, false};
if (!match(CmpRHS, m_APInt(C1)))
return {SPF_UNKNOWN, SPNB_NA, false};
// An unsigned min/max can be written with a signed compare.
const APInt *C2;
if ((CmpLHS == TrueVal && match(FalseVal, m_APInt(C2))) ||
(CmpLHS == FalseVal && match(TrueVal, m_APInt(C2)))) {
// Is the sign bit set?
// (X <s 0) ? X : MAXVAL ==> (X >u MAXVAL) ? X : MAXVAL ==> UMAX
// (X <s 0) ? MAXVAL : X ==> (X >u MAXVAL) ? MAXVAL : X ==> UMIN
if (Pred == CmpInst::ICMP_SLT && *C1 == 0 && C2->isMaxSignedValue())
return {CmpLHS == TrueVal ? SPF_UMAX : SPF_UMIN, SPNB_NA, false};
// Is the sign bit clear?
// (X >s -1) ? MINVAL : X ==> (X <u MINVAL) ? MINVAL : X ==> UMAX
// (X >s -1) ? X : MINVAL ==> (X <u MINVAL) ? X : MINVAL ==> UMIN
if (Pred == CmpInst::ICMP_SGT && C1->isAllOnesValue() &&
C2->isMinSignedValue())
return {CmpLHS == FalseVal ? SPF_UMAX : SPF_UMIN, SPNB_NA, false};
}
// Look through 'not' ops to find disguised signed min/max.
// (X >s C) ? ~X : ~C ==> (~X <s ~C) ? ~X : ~C ==> SMIN(~X, ~C)
// (X <s C) ? ~X : ~C ==> (~X >s ~C) ? ~X : ~C ==> SMAX(~X, ~C)
if (match(TrueVal, m_Not(m_Specific(CmpLHS))) &&
match(FalseVal, m_APInt(C2)) && ~(*C1) == *C2)
return {Pred == CmpInst::ICMP_SGT ? SPF_SMIN : SPF_SMAX, SPNB_NA, false};
// (X >s C) ? ~C : ~X ==> (~X <s ~C) ? ~C : ~X ==> SMAX(~C, ~X)
// (X <s C) ? ~C : ~X ==> (~X >s ~C) ? ~C : ~X ==> SMIN(~C, ~X)
if (match(FalseVal, m_Not(m_Specific(CmpLHS))) &&
match(TrueVal, m_APInt(C2)) && ~(*C1) == *C2)
return {Pred == CmpInst::ICMP_SGT ? SPF_SMAX : SPF_SMIN, SPNB_NA, false};
return {SPF_UNKNOWN, SPNB_NA, false};
}
static SelectPatternResult matchSelectPattern(CmpInst::Predicate Pred,
FastMathFlags FMF,
Value *CmpLHS, Value *CmpRHS,
Value *TrueVal, Value *FalseVal,
Value *&LHS, Value *&RHS) {
LHS = CmpLHS;
RHS = CmpRHS;
// If the predicate is an "or-equal" (FP) predicate, then signed zeroes may
// return inconsistent results between implementations.
// (0.0 <= -0.0) ? 0.0 : -0.0 // Returns 0.0
// minNum(0.0, -0.0) // May return -0.0 or 0.0 (IEEE 754-2008 5.3.1)
// Therefore we behave conservatively and only proceed if at least one of the
// operands is known to not be zero, or if we don't care about signed zeroes.
switch (Pred) {
default: break;
case CmpInst::FCMP_OGE: case CmpInst::FCMP_OLE:
case CmpInst::FCMP_UGE: case CmpInst::FCMP_ULE:
if (!FMF.noSignedZeros() && !isKnownNonZero(CmpLHS) &&
!isKnownNonZero(CmpRHS))
return {SPF_UNKNOWN, SPNB_NA, false};
}
SelectPatternNaNBehavior NaNBehavior = SPNB_NA;
bool Ordered = false;
// When given one NaN and one non-NaN input:
// - maxnum/minnum (C99 fmaxf()/fminf()) return the non-NaN input.
// - A simple C99 (a < b ? a : b) construction will return 'b' (as the
// ordered comparison fails), which could be NaN or non-NaN.
// so here we discover exactly what NaN behavior is required/accepted.
if (CmpInst::isFPPredicate(Pred)) {
bool LHSSafe = isKnownNonNaN(CmpLHS, FMF);
bool RHSSafe = isKnownNonNaN(CmpRHS, FMF);
if (LHSSafe && RHSSafe) {
// Both operands are known non-NaN.
NaNBehavior = SPNB_RETURNS_ANY;
} else if (CmpInst::isOrdered(Pred)) {
// An ordered comparison will return false when given a NaN, so it
// returns the RHS.
Ordered = true;
if (LHSSafe)
// LHS is non-NaN, so if RHS is NaN then NaN will be returned.
NaNBehavior = SPNB_RETURNS_NAN;
else if (RHSSafe)
NaNBehavior = SPNB_RETURNS_OTHER;
else
// Completely unsafe.
return {SPF_UNKNOWN, SPNB_NA, false};
} else {
Ordered = false;
// An unordered comparison will return true when given a NaN, so it
// returns the LHS.
if (LHSSafe)
// LHS is non-NaN, so if RHS is NaN then non-NaN will be returned.
NaNBehavior = SPNB_RETURNS_OTHER;
else if (RHSSafe)
NaNBehavior = SPNB_RETURNS_NAN;
else
// Completely unsafe.
return {SPF_UNKNOWN, SPNB_NA, false};
}
}
if (TrueVal == CmpRHS && FalseVal == CmpLHS) {
std::swap(CmpLHS, CmpRHS);
Pred = CmpInst::getSwappedPredicate(Pred);
if (NaNBehavior == SPNB_RETURNS_NAN)
NaNBehavior = SPNB_RETURNS_OTHER;
else if (NaNBehavior == SPNB_RETURNS_OTHER)
NaNBehavior = SPNB_RETURNS_NAN;
Ordered = !Ordered;
}
// ([if]cmp X, Y) ? X : Y
if (TrueVal == CmpLHS && FalseVal == CmpRHS) {
switch (Pred) {
default: return {SPF_UNKNOWN, SPNB_NA, false}; // Equality.
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE: return {SPF_UMAX, SPNB_NA, false};
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_SGE: return {SPF_SMAX, SPNB_NA, false};
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE: return {SPF_UMIN, SPNB_NA, false};
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_SLE: return {SPF_SMIN, SPNB_NA, false};
case FCmpInst::FCMP_UGT:
case FCmpInst::FCMP_UGE:
case FCmpInst::FCMP_OGT:
case FCmpInst::FCMP_OGE: return {SPF_FMAXNUM, NaNBehavior, Ordered};
case FCmpInst::FCMP_ULT:
case FCmpInst::FCMP_ULE:
case FCmpInst::FCMP_OLT:
case FCmpInst::FCMP_OLE: return {SPF_FMINNUM, NaNBehavior, Ordered};
}
}
const APInt *C1;
if (match(CmpRHS, m_APInt(C1))) {
if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
(CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
// ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
// NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
if (Pred == ICmpInst::ICMP_SGT && (*C1 == 0 || C1->isAllOnesValue())) {
return {(CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
}
// ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
// NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
if (Pred == ICmpInst::ICMP_SLT && (*C1 == 0 || *C1 == 1)) {
return {(CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
}
}
}
return matchMinMax(Pred, CmpLHS, CmpRHS, TrueVal, FalseVal, LHS, RHS);
}
static Value *lookThroughCast(CmpInst *CmpI, Value *V1, Value *V2,
Instruction::CastOps *CastOp) {
auto *Cast1 = dyn_cast<CastInst>(V1);
if (!Cast1)
return nullptr;
*CastOp = Cast1->getOpcode();
Type *SrcTy = Cast1->getSrcTy();
if (auto *Cast2 = dyn_cast<CastInst>(V2)) {
// If V1 and V2 are both the same cast from the same type, look through V1.
if (*CastOp == Cast2->getOpcode() && SrcTy == Cast2->getSrcTy())
return Cast2->getOperand(0);
return nullptr;
}
auto *C = dyn_cast<Constant>(V2);
if (!C)
return nullptr;
Constant *CastedTo = nullptr;
switch (*CastOp) {
case Instruction::ZExt:
if (CmpI->isUnsigned())
CastedTo = ConstantExpr::getTrunc(C, SrcTy);
break;
case Instruction::SExt:
if (CmpI->isSigned())
CastedTo = ConstantExpr::getTrunc(C, SrcTy, true);
break;
case Instruction::Trunc:
CastedTo = ConstantExpr::getIntegerCast(C, SrcTy, CmpI->isSigned());
break;
case Instruction::FPTrunc:
CastedTo = ConstantExpr::getFPExtend(C, SrcTy, true);
break;
case Instruction::FPExt:
CastedTo = ConstantExpr::getFPTrunc(C, SrcTy, true);
break;
case Instruction::FPToUI:
CastedTo = ConstantExpr::getUIToFP(C, SrcTy, true);
break;
case Instruction::FPToSI:
CastedTo = ConstantExpr::getSIToFP(C, SrcTy, true);
break;
case Instruction::UIToFP:
CastedTo = ConstantExpr::getFPToUI(C, SrcTy, true);
break;
case Instruction::SIToFP:
CastedTo = ConstantExpr::getFPToSI(C, SrcTy, true);
break;
default:
break;
}
if (!CastedTo)
return nullptr;
// Make sure the cast doesn't lose any information.
Constant *CastedBack =
ConstantExpr::getCast(*CastOp, CastedTo, C->getType(), true);
if (CastedBack != C)
return nullptr;
return CastedTo;
}
SelectPatternResult llvm::matchSelectPattern(Value *V, Value *&LHS, Value *&RHS,
Instruction::CastOps *CastOp) {
SelectInst *SI = dyn_cast<SelectInst>(V);
if (!SI) return {SPF_UNKNOWN, SPNB_NA, false};
CmpInst *CmpI = dyn_cast<CmpInst>(SI->getCondition());
if (!CmpI) return {SPF_UNKNOWN, SPNB_NA, false};
CmpInst::Predicate Pred = CmpI->getPredicate();
Value *CmpLHS = CmpI->getOperand(0);
Value *CmpRHS = CmpI->getOperand(1);
Value *TrueVal = SI->getTrueValue();
Value *FalseVal = SI->getFalseValue();
FastMathFlags FMF;
if (isa<FPMathOperator>(CmpI))
FMF = CmpI->getFastMathFlags();
// Bail out early.
if (CmpI->isEquality())
return {SPF_UNKNOWN, SPNB_NA, false};
// Deal with type mismatches.
if (CastOp && CmpLHS->getType() != TrueVal->getType()) {
if (Value *C = lookThroughCast(CmpI, TrueVal, FalseVal, CastOp))
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
cast<CastInst>(TrueVal)->getOperand(0), C,
LHS, RHS);
if (Value *C = lookThroughCast(CmpI, FalseVal, TrueVal, CastOp))
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS,
C, cast<CastInst>(FalseVal)->getOperand(0),
LHS, RHS);
}
return ::matchSelectPattern(Pred, FMF, CmpLHS, CmpRHS, TrueVal, FalseVal,
LHS, RHS);
}
/// Return true if "icmp Pred LHS RHS" is always true.
static bool isTruePredicate(CmpInst::Predicate Pred,
const Value *LHS, const Value *RHS,
const DataLayout &DL, unsigned Depth,
AssumptionCache *AC, const Instruction *CxtI,
const DominatorTree *DT) {
assert(!LHS->getType()->isVectorTy() && "TODO: extend to handle vectors!");
if (ICmpInst::isTrueWhenEqual(Pred) && LHS == RHS)
return true;
switch (Pred) {
default:
return false;
case CmpInst::ICMP_SLE: {
const APInt *C;
// LHS s<= LHS +_{nsw} C if C >= 0
if (match(RHS, m_NSWAdd(m_Specific(LHS), m_APInt(C))))
return !C->isNegative();
return false;
}
case CmpInst::ICMP_ULE: {
const APInt *C;
// LHS u<= LHS +_{nuw} C for any C
if (match(RHS, m_NUWAdd(m_Specific(LHS), m_APInt(C))))
return true;
// Match A to (X +_{nuw} CA) and B to (X +_{nuw} CB)
auto MatchNUWAddsToSameValue = [&](const Value *A, const Value *B,
const Value *&X,
const APInt *&CA, const APInt *&CB) {
if (match(A, m_NUWAdd(m_Value(X), m_APInt(CA))) &&
match(B, m_NUWAdd(m_Specific(X), m_APInt(CB))))
return true;
// If X & C == 0 then (X | C) == X +_{nuw} C
if (match(A, m_Or(m_Value(X), m_APInt(CA))) &&
match(B, m_Or(m_Specific(X), m_APInt(CB)))) {
unsigned BitWidth = CA->getBitWidth();
APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
computeKnownBits(X, KnownZero, KnownOne, DL, Depth + 1, AC, CxtI, DT);
if ((KnownZero & *CA) == *CA && (KnownZero & *CB) == *CB)
return true;
}
return false;
};
const Value *X;
const APInt *CLHS, *CRHS;
if (MatchNUWAddsToSameValue(LHS, RHS, X, CLHS, CRHS))
return CLHS->ule(*CRHS);
return false;
}
}
}
/// Return true if "icmp Pred BLHS BRHS" is true whenever "icmp Pred
/// ALHS ARHS" is true. Otherwise, return None.
static Optional<bool>
isImpliedCondOperands(CmpInst::Predicate Pred, const Value *ALHS,
const Value *ARHS, const Value *BLHS,
const Value *BRHS, const DataLayout &DL,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI, const DominatorTree *DT) {
switch (Pred) {
default:
return None;
case CmpInst::ICMP_SLT:
case CmpInst::ICMP_SLE:
if (isTruePredicate(CmpInst::ICMP_SLE, BLHS, ALHS, DL, Depth, AC, CxtI,
DT) &&
isTruePredicate(CmpInst::ICMP_SLE, ARHS, BRHS, DL, Depth, AC, CxtI, DT))
return true;
return None;
case CmpInst::ICMP_ULT:
case CmpInst::ICMP_ULE:
if (isTruePredicate(CmpInst::ICMP_ULE, BLHS, ALHS, DL, Depth, AC, CxtI,
DT) &&
isTruePredicate(CmpInst::ICMP_ULE, ARHS, BRHS, DL, Depth, AC, CxtI, DT))
return true;
return None;
}
}
/// Return true if the operands of the two compares match. IsSwappedOps is true
/// when the operands match, but are swapped.
static bool isMatchingOps(const Value *ALHS, const Value *ARHS,
const Value *BLHS, const Value *BRHS,
bool &IsSwappedOps) {
bool IsMatchingOps = (ALHS == BLHS && ARHS == BRHS);
IsSwappedOps = (ALHS == BRHS && ARHS == BLHS);
return IsMatchingOps || IsSwappedOps;
}
/// Return true if "icmp1 APred ALHS ARHS" implies "icmp2 BPred BLHS BRHS" is
/// true. Return false if "icmp1 APred ALHS ARHS" implies "icmp2 BPred BLHS
/// BRHS" is false. Otherwise, return None if we can't infer anything.
static Optional<bool> isImpliedCondMatchingOperands(CmpInst::Predicate APred,
const Value *ALHS,
const Value *ARHS,
CmpInst::Predicate BPred,
const Value *BLHS,
const Value *BRHS,
bool IsSwappedOps) {
// Canonicalize the operands so they're matching.
if (IsSwappedOps) {
std::swap(BLHS, BRHS);
BPred = ICmpInst::getSwappedPredicate(BPred);
}
if (CmpInst::isImpliedTrueByMatchingCmp(APred, BPred))
return true;
if (CmpInst::isImpliedFalseByMatchingCmp(APred, BPred))
return false;
return None;
}
/// Return true if "icmp1 APred ALHS C1" implies "icmp2 BPred BLHS C2" is
/// true. Return false if "icmp1 APred ALHS C1" implies "icmp2 BPred BLHS
/// C2" is false. Otherwise, return None if we can't infer anything.
static Optional<bool>
isImpliedCondMatchingImmOperands(CmpInst::Predicate APred, const Value *ALHS,
const ConstantInt *C1,
CmpInst::Predicate BPred,
const Value *BLHS, const ConstantInt *C2) {
assert(ALHS == BLHS && "LHS operands must match.");
ConstantRange DomCR =
ConstantRange::makeExactICmpRegion(APred, C1->getValue());
ConstantRange CR =
ConstantRange::makeAllowedICmpRegion(BPred, C2->getValue());
ConstantRange Intersection = DomCR.intersectWith(CR);
ConstantRange Difference = DomCR.difference(CR);
if (Intersection.isEmptySet())
return false;
if (Difference.isEmptySet())
return true;
return None;
}
Optional<bool> llvm::isImpliedCondition(const Value *LHS, const Value *RHS,
const DataLayout &DL, bool InvertAPred,
unsigned Depth, AssumptionCache *AC,
const Instruction *CxtI,
const DominatorTree *DT) {
// A mismatch occurs when we compare a scalar cmp to a vector cmp, for example.
if (LHS->getType() != RHS->getType())
return None;
Type *OpTy = LHS->getType();
assert(OpTy->getScalarType()->isIntegerTy(1));
// LHS ==> RHS by definition
if (!InvertAPred && LHS == RHS)
return true;
if (OpTy->isVectorTy())
// TODO: extending the code below to handle vectors
return None;
assert(OpTy->isIntegerTy(1) && "implied by above");
ICmpInst::Predicate APred, BPred;
Value *ALHS, *ARHS;
Value *BLHS, *BRHS;
if (!match(LHS, m_ICmp(APred, m_Value(ALHS), m_Value(ARHS))) ||
!match(RHS, m_ICmp(BPred, m_Value(BLHS), m_Value(BRHS))))
return None;
if (InvertAPred)
APred = CmpInst::getInversePredicate(APred);
// Can we infer anything when the two compares have matching operands?
bool IsSwappedOps;
if (isMatchingOps(ALHS, ARHS, BLHS, BRHS, IsSwappedOps)) {
if (Optional<bool> Implication = isImpliedCondMatchingOperands(
APred, ALHS, ARHS, BPred, BLHS, BRHS, IsSwappedOps))
return Implication;
// No amount of additional analysis will infer the second condition, so
// early exit.
return None;
}
// Can we infer anything when the LHS operands match and the RHS operands are
// constants (not necessarily matching)?
if (ALHS == BLHS && isa<ConstantInt>(ARHS) && isa<ConstantInt>(BRHS)) {
if (Optional<bool> Implication = isImpliedCondMatchingImmOperands(
APred, ALHS, cast<ConstantInt>(ARHS), BPred, BLHS,
cast<ConstantInt>(BRHS)))
return Implication;
// No amount of additional analysis will infer the second condition, so
// early exit.
return None;
}
if (APred == BPred)
return isImpliedCondOperands(APred, ALHS, ARHS, BLHS, BRHS, DL, Depth, AC,
CxtI, DT);
return None;
}
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