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llvm/lib/Analysis/InstructionSimplify.cpp
Duncan Sands f8b1a5ea96 If we detect that the instruction we are simplifying is unreachable, arrange for 
it to be replaced by undef rather than not replaced at all, the idea being that
this may reduce the amount of work done by whoever called InstructionSimplify.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121860 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-15 11:02:22 +00:00

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//===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements routines for folding instructions into simpler forms
// that do not require creating new instructions. This does constant folding
// ("add i32 1, 1" -> "2") but can also handle non-constant operands, either
// returning a constant ("and i32 %x, 0" -> "0") or an already existing value
// ("and i32 %x, %x" -> "%x").
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/PatternMatch.h"
#include "llvm/Support/ValueHandle.h"
#include "llvm/Target/TargetData.h"
using namespace llvm;
using namespace llvm::PatternMatch;
#define RecursionLimit 3
static Value *SimplifyBinOp(unsigned, Value *, Value *, const TargetData *,
const DominatorTree *, unsigned);
static Value *SimplifyCmpInst(unsigned, Value *, Value *, const TargetData *,
const DominatorTree *, unsigned);
/// ValueDominatesPHI - Does the given value dominate the specified phi node?
static bool ValueDominatesPHI(Value *V, PHINode *P, const DominatorTree *DT) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I)
// Arguments and constants dominate all instructions.
return true;
// If we have a DominatorTree then do a precise test.
if (DT)
return DT->dominates(I, P);
// Otherwise, if the instruction is in the entry block, and is not an invoke,
// then it obviously dominates all phi nodes.
if (I->getParent() == &I->getParent()->getParent()->getEntryBlock() &&
!isa<InvokeInst>(I))
return true;
return false;
}
/// ThreadBinOpOverSelect - In the case of a binary operation with a select
/// instruction as an operand, try to simplify the binop by seeing whether
/// evaluating it on both branches of the select results in the same value.
/// Returns the common value if so, otherwise returns null.
static Value *ThreadBinOpOverSelect(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD,
const DominatorTree *DT,
unsigned MaxRecurse) {
SelectInst *SI;
if (isa<SelectInst>(LHS)) {
SI = cast<SelectInst>(LHS);
} else {
assert(isa<SelectInst>(RHS) && "No select instruction operand!");
SI = cast<SelectInst>(RHS);
}
// Evaluate the BinOp on the true and false branches of the select.
Value *TV;
Value *FV;
if (SI == LHS) {
TV = SimplifyBinOp(Opcode, SI->getTrueValue(), RHS, TD, DT, MaxRecurse);
FV = SimplifyBinOp(Opcode, SI->getFalseValue(), RHS, TD, DT, MaxRecurse);
} else {
TV = SimplifyBinOp(Opcode, LHS, SI->getTrueValue(), TD, DT, MaxRecurse);
FV = SimplifyBinOp(Opcode, LHS, SI->getFalseValue(), TD, DT, MaxRecurse);
}
// If they simplified to the same value, then return the common value.
// If they both failed to simplify then return null.
if (TV == FV)
return TV;
// If one branch simplified to undef, return the other one.
if (TV && isa<UndefValue>(TV))
return FV;
if (FV && isa<UndefValue>(FV))
return TV;
// If applying the operation did not change the true and false select values,
// then the result of the binop is the select itself.
if (TV == SI->getTrueValue() && FV == SI->getFalseValue())
return SI;
// If one branch simplified and the other did not, and the simplified
// value is equal to the unsimplified one, return the simplified value.
// For example, select (cond, X, X & Z) & Z -> X & Z.
if ((FV && !TV) || (TV && !FV)) {
// Check that the simplified value has the form "X op Y" where "op" is the
// same as the original operation.
Instruction *Simplified = dyn_cast<Instruction>(FV ? FV : TV);
if (Simplified && Simplified->getOpcode() == Opcode) {
// The value that didn't simplify is "UnsimplifiedLHS op UnsimplifiedRHS".
// We already know that "op" is the same as for the simplified value. See
// if the operands match too. If so, return the simplified value.
Value *UnsimplifiedBranch = FV ? SI->getTrueValue() : SI->getFalseValue();
Value *UnsimplifiedLHS = SI == LHS ? UnsimplifiedBranch : LHS;
Value *UnsimplifiedRHS = SI == LHS ? RHS : UnsimplifiedBranch;
if (Simplified->getOperand(0) == UnsimplifiedLHS &&
Simplified->getOperand(1) == UnsimplifiedRHS)
return Simplified;
if (Simplified->isCommutative() &&
Simplified->getOperand(1) == UnsimplifiedLHS &&
Simplified->getOperand(0) == UnsimplifiedRHS)
return Simplified;
}
}
return 0;
}
/// ThreadCmpOverSelect - In the case of a comparison with a select instruction,
/// try to simplify the comparison by seeing whether both branches of the select
/// result in the same value. Returns the common value if so, otherwise returns
/// null.
static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
Value *RHS, const TargetData *TD,
const DominatorTree *DT,
unsigned MaxRecurse) {
// Make sure the select is on the LHS.
if (!isa<SelectInst>(LHS)) {
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
assert(isa<SelectInst>(LHS) && "Not comparing with a select instruction!");
SelectInst *SI = cast<SelectInst>(LHS);
// Now that we have "cmp select(cond, TV, FV), RHS", analyse it.
// Does "cmp TV, RHS" simplify?
if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD, DT,
MaxRecurse))
// It does! Does "cmp FV, RHS" simplify?
if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD, DT,
MaxRecurse))
// It does! If they simplified to the same value, then use it as the
// result of the original comparison.
if (TCmp == FCmp)
return TCmp;
return 0;
}
/// ThreadBinOpOverPHI - In the case of a binary operation with an operand that
/// is a PHI instruction, try to simplify the binop by seeing whether evaluating
/// it on the incoming phi values yields the same result for every value. If so
/// returns the common value, otherwise returns null.
static Value *ThreadBinOpOverPHI(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT,
unsigned MaxRecurse) {
PHINode *PI;
if (isa<PHINode>(LHS)) {
PI = cast<PHINode>(LHS);
// Bail out if RHS and the phi may be mutually interdependent due to a loop.
if (!ValueDominatesPHI(RHS, PI, DT))
return 0;
} else {
assert(isa<PHINode>(RHS) && "No PHI instruction operand!");
PI = cast<PHINode>(RHS);
// Bail out if LHS and the phi may be mutually interdependent due to a loop.
if (!ValueDominatesPHI(LHS, PI, DT))
return 0;
}
// Evaluate the BinOp on the incoming phi values.
Value *CommonValue = 0;
for (unsigned i = 0, e = PI->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = PI->getIncomingValue(i);
// If the incoming value is the phi node itself, it can safely be skipped.
if (Incoming == PI) continue;
Value *V = PI == LHS ?
SimplifyBinOp(Opcode, Incoming, RHS, TD, DT, MaxRecurse) :
SimplifyBinOp(Opcode, LHS, Incoming, TD, DT, MaxRecurse);
// If the operation failed to simplify, or simplified to a different value
// to previously, then give up.
if (!V || (CommonValue && V != CommonValue))
return 0;
CommonValue = V;
}
return CommonValue;
}
/// ThreadCmpOverPHI - In the case of a comparison with a PHI instruction, try
/// try to simplify the comparison by seeing whether comparing with all of the
/// incoming phi values yields the same result every time. If so returns the
/// common result, otherwise returns null.
static Value *ThreadCmpOverPHI(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT,
unsigned MaxRecurse) {
// Make sure the phi is on the LHS.
if (!isa<PHINode>(LHS)) {
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
assert(isa<PHINode>(LHS) && "Not comparing with a phi instruction!");
PHINode *PI = cast<PHINode>(LHS);
// Bail out if RHS and the phi may be mutually interdependent due to a loop.
if (!ValueDominatesPHI(RHS, PI, DT))
return 0;
// Evaluate the BinOp on the incoming phi values.
Value *CommonValue = 0;
for (unsigned i = 0, e = PI->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = PI->getIncomingValue(i);
// If the incoming value is the phi node itself, it can safely be skipped.
if (Incoming == PI) continue;
Value *V = SimplifyCmpInst(Pred, Incoming, RHS, TD, DT, MaxRecurse);
// If the operation failed to simplify, or simplified to a different value
// to previously, then give up.
if (!V || (CommonValue && V != CommonValue))
return 0;
CommonValue = V;
}
return CommonValue;
}
/// SimplifyAddInst - Given operands for an Add, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
const TargetData *TD, const DominatorTree *) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
return ConstantFoldInstOperands(Instruction::Add, CLHS->getType(),
Ops, 2, TD);
}
// Canonicalize the constant to the RHS.
std::swap(Op0, Op1);
}
if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
// X + undef -> undef
if (isa<UndefValue>(Op1C))
return Op1C;
// X + 0 --> X
if (Op1C->isNullValue())
return Op0;
}
// FIXME: Could pull several more out of instcombine.
// Threading Add over selects and phi nodes is pointless, so don't bother.
// Threading over the select in "A + select(cond, B, C)" means evaluating
// "A+B" and "A+C" and seeing if they are equal; but they are equal if and
// only if B and C are equal. If B and C are equal then (since we assume
// that operands have already been simplified) "select(cond, B, C)" should
// have been simplified to the common value of B and C already. Analysing
// "A+B" and "A+C" thus gains nothing, but costs compile time. Similarly
// for threading over phi nodes.
return 0;
}
/// SimplifyAndInst - Given operands for an And, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
return ConstantFoldInstOperands(Instruction::And, CLHS->getType(),
Ops, 2, TD);
}
// Canonicalize the constant to the RHS.
std::swap(Op0, Op1);
}
// X & undef -> 0
if (isa<UndefValue>(Op1))
return Constant::getNullValue(Op0->getType());
// X & X = X
if (Op0 == Op1)
return Op0;
// X & 0 = 0
if (match(Op1, m_Zero()))
return Op1;
// X & -1 = X
if (match(Op1, m_AllOnes()))
return Op0;
// A & ~A = ~A & A = 0
Value *A = 0, *B = 0;
if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
(match(Op1, m_Not(m_Value(A))) && A == Op0))
return Constant::getNullValue(Op0->getType());
// (A | ?) & A = A
if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op1;
// A & (A | ?) = A
if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op0;
// (A & B) & A -> A & B
if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op0;
// A & (A & B) -> A & B
if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op1;
// If the operation is with the result of a select instruction, check whether
// operating on either branch of the select always yields the same value.
if (MaxRecurse && (isa<SelectInst>(Op0) || isa<SelectInst>(Op1)))
if (Value *V = ThreadBinOpOverSelect(Instruction::And, Op0, Op1, TD, DT,
MaxRecurse-1))
return V;
// If the operation is with the result of a phi instruction, check whether
// operating on all incoming values of the phi always yields the same value.
if (MaxRecurse && (isa<PHINode>(Op0) || isa<PHINode>(Op1)))
if (Value *V = ThreadBinOpOverPHI(Instruction::And, Op0, Op1, TD, DT,
MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT) {
return ::SimplifyAndInst(Op0, Op1, TD, DT, RecursionLimit);
}
/// SimplifyOrInst - Given operands for an Or, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
return ConstantFoldInstOperands(Instruction::Or, CLHS->getType(),
Ops, 2, TD);
}
// Canonicalize the constant to the RHS.
std::swap(Op0, Op1);
}
// X | undef -> -1
if (isa<UndefValue>(Op1))
return Constant::getAllOnesValue(Op0->getType());
// X | X = X
if (Op0 == Op1)
return Op0;
// X | 0 = X
if (match(Op1, m_Zero()))
return Op0;
// X | -1 = -1
if (match(Op1, m_AllOnes()))
return Op1;
// A | ~A = ~A | A = -1
Value *A = 0, *B = 0;
if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
(match(Op1, m_Not(m_Value(A))) && A == Op0))
return Constant::getAllOnesValue(Op0->getType());
// (A & ?) | A = A
if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op1;
// A | (A & ?) = A
if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op0;
// (A | B) | A -> A | B
if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op0;
// A | (A | B) -> A | B
if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op1;
// If the operation is with the result of a select instruction, check whether
// operating on either branch of the select always yields the same value.
if (MaxRecurse && (isa<SelectInst>(Op0) || isa<SelectInst>(Op1)))
if (Value *V = ThreadBinOpOverSelect(Instruction::Or, Op0, Op1, TD, DT,
MaxRecurse-1))
return V;
// If the operation is with the result of a phi instruction, check whether
// operating on all incoming values of the phi always yields the same value.
if (MaxRecurse && (isa<PHINode>(Op0) || isa<PHINode>(Op1)))
if (Value *V = ThreadBinOpOverPHI(Instruction::Or, Op0, Op1, TD, DT,
MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT) {
return ::SimplifyOrInst(Op0, Op1, TD, DT, RecursionLimit);
}
/// SimplifyXorInst - Given operands for a Xor, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyXorInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
return ConstantFoldInstOperands(Instruction::Xor, CLHS->getType(),
Ops, 2, TD);
}
// Canonicalize the constant to the RHS.
std::swap(Op0, Op1);
}
// A ^ undef -> undef
if (isa<UndefValue>(Op1))
return Op1;
// A ^ 0 = A
if (match(Op1, m_Zero()))
return Op0;
// A ^ A = 0
if (Op0 == Op1)
return Constant::getNullValue(Op0->getType());
// A ^ ~A = ~A ^ A = -1
Value *A = 0, *B = 0;
if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
(match(Op1, m_Not(m_Value(A))) && A == Op0))
return Constant::getAllOnesValue(Op0->getType());
// (A ^ B) ^ A = B
if (match(Op0, m_Xor(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return A == Op1 ? B : A;
// A ^ (A ^ B) = B
if (match(Op1, m_Xor(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return A == Op0 ? B : A;
// Threading Xor over selects and phi nodes is pointless, so don't bother.
// Threading over the select in "A ^ select(cond, B, C)" means evaluating
// "A^B" and "A^C" and seeing if they are equal; but they are equal if and
// only if B and C are equal. If B and C are equal then (since we assume
// that operands have already been simplified) "select(cond, B, C)" should
// have been simplified to the common value of B and C already. Analysing
// "A^B" and "A^C" thus gains nothing, but costs compile time. Similarly
// for threading over phi nodes.
return 0;
}
Value *llvm::SimplifyXorInst(Value *Op0, Value *Op1, const TargetData *TD,
const DominatorTree *DT) {
return ::SimplifyXorInst(Op0, Op1, TD, DT, RecursionLimit);
}
static const Type *GetCompareTy(Value *Op) {
return CmpInst::makeCmpResultType(Op->getType());
}
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT,
unsigned MaxRecurse) {
CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
if (Constant *CRHS = dyn_cast<Constant>(RHS))
return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
// If we have a constant, make sure it is on the RHS.
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
// ITy - This is the return type of the compare we're considering.
const Type *ITy = GetCompareTy(LHS);
// icmp X, X -> true/false
// X icmp undef -> true/false. For example, icmp ugt %X, undef -> false
// because X could be 0.
if (LHS == RHS || isa<UndefValue>(RHS))
return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
// icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
// addresses never equal each other! We already know that Op0 != Op1.
if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
isa<ConstantPointerNull>(LHS)) &&
(isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
isa<ConstantPointerNull>(RHS)))
return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
// See if we are doing a comparison with a constant.
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
// If we have an icmp le or icmp ge instruction, turn it into the
// appropriate icmp lt or icmp gt instruction. This allows us to rely on
// them being folded in the code below.
switch (Pred) {
default: break;
case ICmpInst::ICMP_ULE:
if (CI->isMaxValue(false)) // A <=u MAX -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
case ICmpInst::ICMP_SLE:
if (CI->isMaxValue(true)) // A <=s MAX -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
case ICmpInst::ICMP_UGE:
if (CI->isMinValue(false)) // A >=u MIN -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
case ICmpInst::ICMP_SGE:
if (CI->isMinValue(true)) // A >=s MIN -> TRUE
return ConstantInt::getTrue(CI->getContext());
break;
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (MaxRecurse && (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD, DT, MaxRecurse-1))
return V;
// If the comparison is with the result of a phi instruction, check whether
// doing the compare with each incoming phi value yields a common result.
if (MaxRecurse && (isa<PHINode>(LHS) || isa<PHINode>(RHS)))
if (Value *V = ThreadCmpOverPHI(Pred, LHS, RHS, TD, DT, MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT) {
return ::SimplifyICmpInst(Predicate, LHS, RHS, TD, DT, RecursionLimit);
}
/// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT,
unsigned MaxRecurse) {
CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
if (Constant *CRHS = dyn_cast<Constant>(RHS))
return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
// If we have a constant, make sure it is on the RHS.
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
// Fold trivial predicates.
if (Pred == FCmpInst::FCMP_FALSE)
return ConstantInt::get(GetCompareTy(LHS), 0);
if (Pred == FCmpInst::FCMP_TRUE)
return ConstantInt::get(GetCompareTy(LHS), 1);
if (isa<UndefValue>(RHS)) // fcmp pred X, undef -> undef
return UndefValue::get(GetCompareTy(LHS));
// fcmp x,x -> true/false. Not all compares are foldable.
if (LHS == RHS) {
if (CmpInst::isTrueWhenEqual(Pred))
return ConstantInt::get(GetCompareTy(LHS), 1);
if (CmpInst::isFalseWhenEqual(Pred))
return ConstantInt::get(GetCompareTy(LHS), 0);
}
// Handle fcmp with constant RHS
if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
// If the constant is a nan, see if we can fold the comparison based on it.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
if (CFP->getValueAPF().isNaN()) {
if (FCmpInst::isOrdered(Pred)) // True "if ordered and foo"
return ConstantInt::getFalse(CFP->getContext());
assert(FCmpInst::isUnordered(Pred) &&
"Comparison must be either ordered or unordered!");
// True if unordered.
return ConstantInt::getTrue(CFP->getContext());
}
// Check whether the constant is an infinity.
if (CFP->getValueAPF().isInfinity()) {
if (CFP->getValueAPF().isNegative()) {
switch (Pred) {
case FCmpInst::FCMP_OLT:
// No value is ordered and less than negative infinity.
return ConstantInt::getFalse(CFP->getContext());
case FCmpInst::FCMP_UGE:
// All values are unordered with or at least negative infinity.
return ConstantInt::getTrue(CFP->getContext());
default:
break;
}
} else {
switch (Pred) {
case FCmpInst::FCMP_OGT:
// No value is ordered and greater than infinity.
return ConstantInt::getFalse(CFP->getContext());
case FCmpInst::FCMP_ULE:
// All values are unordered with and at most infinity.
return ConstantInt::getTrue(CFP->getContext());
default:
break;
}
}
}
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (MaxRecurse && (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD, DT, MaxRecurse-1))
return V;
// If the comparison is with the result of a phi instruction, check whether
// doing the compare with each incoming phi value yields a common result.
if (MaxRecurse && (isa<PHINode>(LHS) || isa<PHINode>(RHS)))
if (Value *V = ThreadCmpOverPHI(Pred, LHS, RHS, TD, DT, MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT) {
return ::SimplifyFCmpInst(Predicate, LHS, RHS, TD, DT, RecursionLimit);
}
/// SimplifySelectInst - Given operands for a SelectInst, see if we can fold
/// the result. If not, this returns null.
Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
const TargetData *TD, const DominatorTree *) {
// select true, X, Y -> X
// select false, X, Y -> Y
if (ConstantInt *CB = dyn_cast<ConstantInt>(CondVal))
return CB->getZExtValue() ? TrueVal : FalseVal;
// select C, X, X -> X
if (TrueVal == FalseVal)
return TrueVal;
if (isa<UndefValue>(TrueVal)) // select C, undef, X -> X
return FalseVal;
if (isa<UndefValue>(FalseVal)) // select C, X, undef -> X
return TrueVal;
if (isa<UndefValue>(CondVal)) { // select undef, X, Y -> X or Y
if (isa<Constant>(TrueVal))
return TrueVal;
return FalseVal;
}
return 0;
}
/// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
const TargetData *TD, const DominatorTree *) {
// The type of the GEP pointer operand.
const PointerType *PtrTy = cast<PointerType>(Ops[0]->getType());
// getelementptr P -> P.
if (NumOps == 1)
return Ops[0];
if (isa<UndefValue>(Ops[0])) {
// Compute the (pointer) type returned by the GEP instruction.
const Type *LastType = GetElementPtrInst::getIndexedType(PtrTy, &Ops[1],
NumOps-1);
const Type *GEPTy = PointerType::get(LastType, PtrTy->getAddressSpace());
return UndefValue::get(GEPTy);
}
if (NumOps == 2) {
// getelementptr P, 0 -> P.
if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
if (C->isZero())
return Ops[0];
// getelementptr P, N -> P if P points to a type of zero size.
if (TD) {
const Type *Ty = PtrTy->getElementType();
if (Ty->isSized() && TD->getTypeAllocSize(Ty) == 0)
return Ops[0];
}
}
// Check to see if this is constant foldable.
for (unsigned i = 0; i != NumOps; ++i)
if (!isa<Constant>(Ops[i]))
return 0;
return ConstantExpr::getGetElementPtr(cast<Constant>(Ops[0]),
(Constant *const*)Ops+1, NumOps-1);
}
/// SimplifyPHINode - See if we can fold the given phi. If not, returns null.
static Value *SimplifyPHINode(PHINode *PN, const DominatorTree *DT) {
// If all of the PHI's incoming values are the same then replace the PHI node
// with the common value.
Value *CommonValue = 0;
bool HasUndefInput = false;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *Incoming = PN->getIncomingValue(i);
// If the incoming value is the phi node itself, it can safely be skipped.
if (Incoming == PN) continue;
if (isa<UndefValue>(Incoming)) {
// Remember that we saw an undef value, but otherwise ignore them.
HasUndefInput = true;
continue;
}
if (CommonValue && Incoming != CommonValue)
return 0; // Not the same, bail out.
CommonValue = Incoming;
}
// If CommonValue is null then all of the incoming values were either undef or
// equal to the phi node itself.
if (!CommonValue)
return UndefValue::get(PN->getType());
// If we have a PHI node like phi(X, undef, X), where X is defined by some
// instruction, we cannot return X as the result of the PHI node unless it
// dominates the PHI block.
if (HasUndefInput)
return ValueDominatesPHI(CommonValue, PN, DT) ? CommonValue : 0;
return CommonValue;
}
//=== Helper functions for higher up the class hierarchy.
/// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT,
unsigned MaxRecurse) {
switch (Opcode) {
case Instruction::And: return SimplifyAndInst(LHS, RHS, TD, DT, MaxRecurse);
case Instruction::Or: return SimplifyOrInst(LHS, RHS, TD, DT, MaxRecurse);
default:
if (Constant *CLHS = dyn_cast<Constant>(LHS))
if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
Constant *COps[] = {CLHS, CRHS};
return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
}
// If the operation is with the result of a select instruction, check whether
// operating on either branch of the select always yields the same value.
if (MaxRecurse && (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)))
if (Value *V = ThreadBinOpOverSelect(Opcode, LHS, RHS, TD, DT,
MaxRecurse-1))
return V;
// If the operation is with the result of a phi instruction, check whether
// operating on all incoming values of the phi always yields the same value.
if (MaxRecurse && (isa<PHINode>(LHS) || isa<PHINode>(RHS)))
if (Value *V = ThreadBinOpOverPHI(Opcode, LHS, RHS, TD, DT, MaxRecurse-1))
return V;
return 0;
}
}
Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT) {
return ::SimplifyBinOp(Opcode, LHS, RHS, TD, DT, RecursionLimit);
}
/// SimplifyCmpInst - Given operands for a CmpInst, see if we can
/// fold the result.
static Value *SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT,
unsigned MaxRecurse) {
if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
return SimplifyICmpInst(Predicate, LHS, RHS, TD, DT, MaxRecurse);
return SimplifyFCmpInst(Predicate, LHS, RHS, TD, DT, MaxRecurse);
}
Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, const DominatorTree *DT) {
return ::SimplifyCmpInst(Predicate, LHS, RHS, TD, DT, RecursionLimit);
}
/// SimplifyInstruction - See if we can compute a simplified version of this
/// instruction. If not, this returns null.
Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD,
const DominatorTree *DT) {
Value *Result;
switch (I->getOpcode()) {
default:
Result = ConstantFoldInstruction(I, TD);
break;
case Instruction::Add:
Result = SimplifyAddInst(I->getOperand(0), I->getOperand(1),
cast<BinaryOperator>(I)->hasNoSignedWrap(),
cast<BinaryOperator>(I)->hasNoUnsignedWrap(),
TD, DT);
break;
case Instruction::And:
Result = SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::Or:
Result = SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::Xor:
Result = SimplifyXorInst(I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::ICmp:
Result = SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::FCmp:
Result = SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
I->getOperand(0), I->getOperand(1), TD, DT);
break;
case Instruction::Select:
Result = SimplifySelectInst(I->getOperand(0), I->getOperand(1),
I->getOperand(2), TD, DT);
break;
case Instruction::GetElementPtr: {
SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
Result = SimplifyGEPInst(&Ops[0], Ops.size(), TD, DT);
break;
}
case Instruction::PHI:
Result = SimplifyPHINode(cast<PHINode>(I), DT);
break;
}
/// If called on unreachable code, the above logic may report that the
/// instruction simplified to itself. Make life easier for users by
/// detecting that case here, returning a safe value instead.
return Result == I ? UndefValue::get(I->getType()) : Result;
}
/// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
/// delete the From instruction. In addition to a basic RAUW, this does a
/// recursive simplification of the newly formed instructions. This catches
/// things where one simplification exposes other opportunities. This only
/// simplifies and deletes scalar operations, it does not change the CFG.
///
void llvm::ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
const TargetData *TD,
const DominatorTree *DT) {
assert(From != To && "ReplaceAndSimplifyAllUses(X,X) is not valid!");
// FromHandle/ToHandle - This keeps a WeakVH on the from/to values so that
// we can know if it gets deleted out from under us or replaced in a
// recursive simplification.
WeakVH FromHandle(From);
WeakVH ToHandle(To);
while (!From->use_empty()) {
// Update the instruction to use the new value.
Use &TheUse = From->use_begin().getUse();
Instruction *User = cast<Instruction>(TheUse.getUser());
TheUse = To;
// Check to see if the instruction can be folded due to the operand
// replacement. For example changing (or X, Y) into (or X, -1) can replace
// the 'or' with -1.
Value *SimplifiedVal;
{
// Sanity check to make sure 'User' doesn't dangle across
// SimplifyInstruction.
AssertingVH<> UserHandle(User);
SimplifiedVal = SimplifyInstruction(User, TD, DT);
if (SimplifiedVal == 0) continue;
}
// Recursively simplify this user to the new value.
ReplaceAndSimplifyAllUses(User, SimplifiedVal, TD, DT);
From = dyn_cast_or_null<Instruction>((Value*)FromHandle);
To = ToHandle;
assert(ToHandle && "To value deleted by recursive simplification?");
// If the recursive simplification ended up revisiting and deleting
// 'From' then we're done.
if (From == 0)
return;
}
// If 'From' has value handles referring to it, do a real RAUW to update them.
From->replaceAllUsesWith(To);
From->eraseFromParent();
}
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