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llvm/lib/Analysis/LazyValueInfo.cpp
Philip Reames 1758dd66cc [LVI] Fix a bug which prevented use of !range metadata within a query 
The diff is relatively large since I took a chance to rearrange the code I had to touch in a more obvious way, but the key bit is merely using the !range metadata when we can't analyze the instruction further.  The previous !range metadata code was essentially just dead since no binary operator or cast will have !range metadata (per Verifier) and it was otherwise dropped on the floor.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@262751 91177308-0d34-0410-b5e6-96231b3b80d8
2016-03-04 22:27:39 +00:00

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//===- LazyValueInfo.cpp - Value constraint analysis ------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the interface for lazy computation of value constraint
// information.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
#include <stack>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "lazy-value-info"
char LazyValueInfo::ID = 0;
INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
namespace llvm {
FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
}
//===----------------------------------------------------------------------===//
// LVILatticeVal
//===----------------------------------------------------------------------===//
/// This is the information tracked by LazyValueInfo for each value.
///
/// FIXME: This is basically just for bringup, this can be made a lot more rich
/// in the future.
///
namespace {
class LVILatticeVal {
enum LatticeValueTy {
/// This Value has no known value yet.
undefined,
/// This Value has a specific constant value.
constant,
/// This Value is known to not have the specified value.
notconstant,
/// The Value falls within this range.
constantrange,
/// This value is not known to be constant, and we know that it has a value.
overdefined
};
/// Val: This stores the current lattice value along with the Constant* for
/// the constant if this is a 'constant' or 'notconstant' value.
LatticeValueTy Tag;
Constant *Val;
ConstantRange Range;
public:
LVILatticeVal() : Tag(undefined), Val(nullptr), Range(1, true) {}
static LVILatticeVal get(Constant *C) {
LVILatticeVal Res;
if (!isa<UndefValue>(C))
Res.markConstant(C);
return Res;
}
static LVILatticeVal getNot(Constant *C) {
LVILatticeVal Res;
if (!isa<UndefValue>(C))
Res.markNotConstant(C);
return Res;
}
static LVILatticeVal getRange(ConstantRange CR) {
LVILatticeVal Res;
Res.markConstantRange(std::move(CR));
return Res;
}
static LVILatticeVal getOverdefined() {
LVILatticeVal Res;
Res.markOverdefined();
return Res;
}
bool isUndefined() const { return Tag == undefined; }
bool isConstant() const { return Tag == constant; }
bool isNotConstant() const { return Tag == notconstant; }
bool isConstantRange() const { return Tag == constantrange; }
bool isOverdefined() const { return Tag == overdefined; }
Constant *getConstant() const {
assert(isConstant() && "Cannot get the constant of a non-constant!");
return Val;
}
Constant *getNotConstant() const {
assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
return Val;
}
ConstantRange getConstantRange() const {
assert(isConstantRange() &&
"Cannot get the constant-range of a non-constant-range!");
return Range;
}
/// Return true if this is a change in status.
bool markOverdefined() {
if (isOverdefined())
return false;
Tag = overdefined;
return true;
}
/// Return true if this is a change in status.
bool markConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return markConstantRange(ConstantRange(CI->getValue()));
if (isa<UndefValue>(V))
return false;
assert((!isConstant() || getConstant() == V) &&
"Marking constant with different value");
assert(isUndefined());
Tag = constant;
Val = V;
return true;
}
/// Return true if this is a change in status.
bool markNotConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
if (isa<UndefValue>(V))
return false;
assert((!isConstant() || getConstant() != V) &&
"Marking constant !constant with same value");
assert((!isNotConstant() || getNotConstant() == V) &&
"Marking !constant with different value");
assert(isUndefined() || isConstant());
Tag = notconstant;
Val = V;
return true;
}
/// Return true if this is a change in status.
bool markConstantRange(ConstantRange NewR) {
if (isConstantRange()) {
if (NewR.isEmptySet())
return markOverdefined();
bool changed = Range != NewR;
Range = std::move(NewR);
return changed;
}
assert(isUndefined());
if (NewR.isEmptySet())
return markOverdefined();
Tag = constantrange;
Range = std::move(NewR);
return true;
}
/// Merge the specified lattice value into this one, updating this
/// one and returning true if anything changed.
bool mergeIn(const LVILatticeVal &RHS, const DataLayout &DL) {
if (RHS.isUndefined() || isOverdefined()) return false;
if (RHS.isOverdefined()) return markOverdefined();
if (isUndefined()) {
Tag = RHS.Tag;
Val = RHS.Val;
Range = RHS.Range;
return true;
}
if (isConstant()) {
if (RHS.isConstant()) {
if (Val == RHS.Val)
return false;
return markOverdefined();
}
if (RHS.isNotConstant()) {
if (Val == RHS.Val)
return markOverdefined();
// Unless we can prove that the two Constants are different, we must
// move to overdefined.
if (ConstantInt *Res =
dyn_cast<ConstantInt>(ConstantFoldCompareInstOperands(
CmpInst::ICMP_NE, getConstant(), RHS.getNotConstant(), DL)))
if (Res->isOne())
return markNotConstant(RHS.getNotConstant());
return markOverdefined();
}
// RHS is a ConstantRange, LHS is a non-integer Constant.
// FIXME: consider the case where RHS is a range [1, 0) and LHS is
// a function. The correct result is to pick up RHS.
return markOverdefined();
}
if (isNotConstant()) {
if (RHS.isConstant()) {
if (Val == RHS.Val)
return markOverdefined();
// Unless we can prove that the two Constants are different, we must
// move to overdefined.
if (ConstantInt *Res =
dyn_cast<ConstantInt>(ConstantFoldCompareInstOperands(
CmpInst::ICMP_NE, getNotConstant(), RHS.getConstant(), DL)))
if (Res->isOne())
return false;
return markOverdefined();
}
if (RHS.isNotConstant()) {
if (Val == RHS.Val)
return false;
return markOverdefined();
}
return markOverdefined();
}
assert(isConstantRange() && "New LVILattice type?");
if (!RHS.isConstantRange())
return markOverdefined();
ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
if (NewR.isFullSet())
return markOverdefined();
return markConstantRange(NewR);
}
};
} // end anonymous namespace.
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
LLVM_ATTRIBUTE_USED;
raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
if (Val.isUndefined())
return OS << "undefined";
if (Val.isOverdefined())
return OS << "overdefined";
if (Val.isNotConstant())
return OS << "notconstant<" << *Val.getNotConstant() << '>';
else if (Val.isConstantRange())
return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
<< Val.getConstantRange().getUpper() << '>';
return OS << "constant<" << *Val.getConstant() << '>';
}
}
/// Returns true if this lattice value represents at most one possible value.
/// This is as precise as any lattice value can get while still representing
/// reachable code.
static bool hasSingleValue(LVILatticeVal Val) {
if (Val.isConstantRange() &&
Val.getConstantRange().isSingleElement())
// Integer constants are single element ranges
return true;
if (Val.isConstant())
// Non integer constants
return true;
return false;
}
/// Combine two sets of facts about the same value into a single set of
/// facts. Note that this method is not suitable for merging facts along
/// different paths in a CFG; that's what the mergeIn function is for. This
/// is for merging facts gathered about the same value at the same location
/// through two independent means.
/// Notes:
/// * This method does not promise to return the most precise possible lattice
/// value implied by A and B. It is allowed to return any lattice element
/// which is at least as strong as *either* A or B (unless our facts
/// conflict, see below).
/// * Due to unreachable code, the intersection of two lattice values could be
/// contradictory. If this happens, we return some valid lattice value so as
/// not confuse the rest of LVI. Ideally, we'd always return Undefined, but
/// we do not make this guarantee. TODO: This would be a useful enhancement.
static LVILatticeVal intersect(LVILatticeVal A, LVILatticeVal B) {
// Undefined is the strongest state. It means the value is known to be along
// an unreachable path.
if (A.isUndefined())
return A;
if (B.isUndefined())
return B;
// If we gave up for one, but got a useable fact from the other, use it.
if (A.isOverdefined())
return B;
if (B.isOverdefined())
return A;
// Can't get any more precise than constants.
if (hasSingleValue(A))
return A;
if (hasSingleValue(B))
return B;
// Could be either constant range or not constant here.
if (!A.isConstantRange() || !B.isConstantRange()) {
// TODO: Arbitrary choice, could be improved
return A;
}
// Intersect two constant ranges
ConstantRange Range =
A.getConstantRange().intersectWith(B.getConstantRange());
// Note: An empty range is implicitly converted to overdefined internally.
// TODO: We could instead use Undefined here since we've proven a conflict
// and thus know this path must be unreachable.
return LVILatticeVal::getRange(std::move(Range));
}
//===----------------------------------------------------------------------===//
// LazyValueInfoCache Decl
//===----------------------------------------------------------------------===//
namespace {
/// A callback value handle updates the cache when values are erased.
class LazyValueInfoCache;
struct LVIValueHandle final : public CallbackVH {
LazyValueInfoCache *Parent;
LVIValueHandle(Value *V, LazyValueInfoCache *P)
: CallbackVH(V), Parent(P) { }
void deleted() override;
void allUsesReplacedWith(Value *V) override {
deleted();
}
};
}
namespace {
/// This is the cache kept by LazyValueInfo which
/// maintains information about queries across the clients' queries.
class LazyValueInfoCache {
/// This is all of the cached block information for exactly one Value*.
/// The entries are sorted by the BasicBlock* of the
/// entries, allowing us to do a lookup with a binary search.
/// Over-defined lattice values are recorded in OverDefinedCache to reduce
/// memory overhead.
typedef SmallDenseMap<AssertingVH<BasicBlock>, LVILatticeVal, 4>
ValueCacheEntryTy;
/// This is all of the cached information for all values,
/// mapped from Value* to key information.
std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
/// This tracks, on a per-block basis, the set of values that are
/// over-defined at the end of that block.
typedef DenseMap<AssertingVH<BasicBlock>, SmallPtrSet<Value *, 4>>
OverDefinedCacheTy;
OverDefinedCacheTy OverDefinedCache;
/// Keep track of all blocks that we have ever seen, so we
/// don't spend time removing unused blocks from our caches.
DenseSet<AssertingVH<BasicBlock> > SeenBlocks;
/// This stack holds the state of the value solver during a query.
/// It basically emulates the callstack of the naive
/// recursive value lookup process.
std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
/// Keeps track of which block-value pairs are in BlockValueStack.
DenseSet<std::pair<BasicBlock*, Value*> > BlockValueSet;
/// Push BV onto BlockValueStack unless it's already in there.
/// Returns true on success.
bool pushBlockValue(const std::pair<BasicBlock *, Value *> &BV) {
if (!BlockValueSet.insert(BV).second)
return false; // It's already in the stack.
DEBUG(dbgs() << "PUSH: " << *BV.second << " in " << BV.first->getName()
<< "\n");
BlockValueStack.push(BV);
return true;
}
AssumptionCache *AC; ///< A pointer to the cache of @llvm.assume calls.
const DataLayout &DL; ///< A mandatory DataLayout
DominatorTree *DT; ///< An optional DT pointer.
friend struct LVIValueHandle;
void insertResult(Value *Val, BasicBlock *BB, const LVILatticeVal &Result) {
SeenBlocks.insert(BB);
// Insert over-defined values into their own cache to reduce memory
// overhead.
if (Result.isOverdefined())
OverDefinedCache[BB].insert(Val);
else
lookup(Val)[BB] = Result;
}
LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
LVILatticeVal &Result,
Instruction *CxtI = nullptr);
bool hasBlockValue(Value *Val, BasicBlock *BB);
// These methods process one work item and may add more. A false value
// returned means that the work item was not completely processed and must
// be revisited after going through the new items.
bool solveBlockValue(Value *Val, BasicBlock *BB);
bool solveBlockValueNonLocal(LVILatticeVal &BBLV,
Value *Val, BasicBlock *BB);
bool solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB);
bool solveBlockValueSelect(LVILatticeVal &BBLV,
SelectInst *S, BasicBlock *BB);
bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI, BasicBlock *BB);
void intersectAssumeBlockValueConstantRange(Value *Val, LVILatticeVal &BBLV,
Instruction *BBI);
void solve();
ValueCacheEntryTy &lookup(Value *V) {
return ValueCache[LVIValueHandle(V, this)];
}
bool isOverdefined(Value *V, BasicBlock *BB) const {
auto ODI = OverDefinedCache.find(BB);
if (ODI == OverDefinedCache.end())
return false;
return ODI->second.count(V);
}
bool hasCachedValueInfo(Value *V, BasicBlock *BB) {
if (isOverdefined(V, BB))
return true;
LVIValueHandle ValHandle(V, this);
auto I = ValueCache.find(ValHandle);
if (I == ValueCache.end())
return false;
return I->second.count(BB);
}
LVILatticeVal getCachedValueInfo(Value *V, BasicBlock *BB) {
if (isOverdefined(V, BB))
return LVILatticeVal::getOverdefined();
return lookup(V)[BB];
}
public:
/// This is the query interface to determine the lattice
/// value for the specified Value* at the end of the specified block.
LVILatticeVal getValueInBlock(Value *V, BasicBlock *BB,
Instruction *CxtI = nullptr);
/// This is the query interface to determine the lattice
/// value for the specified Value* at the specified instruction (generally
/// from an assume intrinsic).
LVILatticeVal getValueAt(Value *V, Instruction *CxtI);
/// This is the query interface to determine the lattice
/// value for the specified Value* that is true on the specified edge.
LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB,
Instruction *CxtI = nullptr);
/// This is the update interface to inform the cache that an edge from
/// PredBB to OldSucc has been threaded to be from PredBB to NewSucc.
void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
/// This is part of the update interface to inform the cache
/// that a block has been deleted.
void eraseBlock(BasicBlock *BB);
/// clear - Empty the cache.
void clear() {
SeenBlocks.clear();
ValueCache.clear();
OverDefinedCache.clear();
}
LazyValueInfoCache(AssumptionCache *AC, const DataLayout &DL,
DominatorTree *DT = nullptr)
: AC(AC), DL(DL), DT(DT) {}
};
} // end anonymous namespace
void LVIValueHandle::deleted() {
SmallVector<AssertingVH<BasicBlock>, 4> ToErase;
for (auto &I : Parent->OverDefinedCache) {
SmallPtrSetImpl<Value *> &ValueSet = I.second;
if (ValueSet.count(getValPtr()))
ValueSet.erase(getValPtr());
if (ValueSet.empty())
ToErase.push_back(I.first);
}
for (auto &BB : ToErase)
Parent->OverDefinedCache.erase(BB);
// This erasure deallocates *this, so it MUST happen after we're done
// using any and all members of *this.
Parent->ValueCache.erase(*this);
}
void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
// Shortcut if we have never seen this block.
DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
if (I == SeenBlocks.end())
return;
SeenBlocks.erase(I);
auto ODI = OverDefinedCache.find(BB);
if (ODI != OverDefinedCache.end())
OverDefinedCache.erase(ODI);
for (auto I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
I->second.erase(BB);
}
void LazyValueInfoCache::solve() {
while (!BlockValueStack.empty()) {
std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
assert(BlockValueSet.count(e) && "Stack value should be in BlockValueSet!");
if (solveBlockValue(e.second, e.first)) {
// The work item was completely processed.
assert(BlockValueStack.top() == e && "Nothing should have been pushed!");
assert(hasCachedValueInfo(e.second, e.first) &&
"Result should be in cache!");
DEBUG(dbgs() << "POP " << *e.second << " in " << e.first->getName()
<< " = " << getCachedValueInfo(e.second, e.first) << "\n");
BlockValueStack.pop();
BlockValueSet.erase(e);
} else {
// More work needs to be done before revisiting.
assert(BlockValueStack.top() != e && "Stack should have been pushed!");
}
}
}
bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (isa<Constant>(Val))
return true;
return hasCachedValueInfo(Val, BB);
}
LVILatticeVal LazyValueInfoCache::getBlockValue(Value *Val, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val))
return LVILatticeVal::get(VC);
SeenBlocks.insert(BB);
return getCachedValueInfo(Val, BB);
}
static LVILatticeVal getFromRangeMetadata(Instruction *BBI) {
switch (BBI->getOpcode()) {
default: break;
case Instruction::Load:
case Instruction::Call:
case Instruction::Invoke:
if (MDNode *Ranges = BBI->getMetadata(LLVMContext::MD_range))
if (isa<IntegerType>(BBI->getType())) {
return LVILatticeVal::getRange(getConstantRangeFromMetadata(*Ranges));
}
break;
};
// Nothing known - will be intersected with other facts
return LVILatticeVal::getOverdefined();
}
bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
if (isa<Constant>(Val))
return true;
if (hasCachedValueInfo(Val, BB)) {
// If we have a cached value, use that.
DEBUG(dbgs() << " reuse BB '" << BB->getName()
<< "' val=" << getCachedValueInfo(Val, BB) << '\n');
// Since we're reusing a cached value, we don't need to update the
// OverDefinedCache. The cache will have been properly updated whenever the
// cached value was inserted.
return true;
}
// Hold off inserting this value into the Cache in case we have to return
// false and come back later.
LVILatticeVal Res;
Instruction *BBI = dyn_cast<Instruction>(Val);
if (!BBI || BBI->getParent() != BB) {
if (!solveBlockValueNonLocal(Res, Val, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
if (!solveBlockValuePHINode(Res, PN, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
if (auto *SI = dyn_cast<SelectInst>(BBI)) {
if (!solveBlockValueSelect(Res, SI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
// If this value is a nonnull pointer, record it's range and bailout.
PointerType *PT = dyn_cast<PointerType>(BBI->getType());
if (PT && isKnownNonNull(BBI)) {
Res = LVILatticeVal::getNot(ConstantPointerNull::get(PT));
insertResult(Val, BB, Res);
return true;
}
if (isa<CastInst>(BBI) && BBI->getType()->isIntegerTy()) {
if (!solveBlockValueConstantRange(Res, BBI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
if (BO && isa<ConstantInt>(BO->getOperand(1))) {
if (!solveBlockValueConstantRange(Res, BBI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - unknown inst def found.\n");
Res = getFromRangeMetadata(BBI);
insertResult(Val, BB, Res);
return true;
}
static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
if (LoadInst *L = dyn_cast<LoadInst>(I)) {
return L->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(L->getPointerOperand(),
L->getModule()->getDataLayout()) == Ptr;
}
if (StoreInst *S = dyn_cast<StoreInst>(I)) {
return S->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(S->getPointerOperand(),
S->getModule()->getDataLayout()) == Ptr;
}
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
if (MI->isVolatile()) return false;
// FIXME: check whether it has a valuerange that excludes zero?
ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
if (!Len || Len->isZero()) return false;
if (MI->getDestAddressSpace() == 0)
if (GetUnderlyingObject(MI->getRawDest(),
MI->getModule()->getDataLayout()) == Ptr)
return true;
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
if (MTI->getSourceAddressSpace() == 0)
if (GetUnderlyingObject(MTI->getRawSource(),
MTI->getModule()->getDataLayout()) == Ptr)
return true;
}
return false;
}
bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
Value *Val, BasicBlock *BB) {
LVILatticeVal Result; // Start Undefined.
// If this is a pointer, and there's a load from that pointer in this BB,
// then we know that the pointer can't be NULL.
bool NotNull = false;
if (Val->getType()->isPointerTy()) {
if (isKnownNonNull(Val)) {
NotNull = true;
} else {
const DataLayout &DL = BB->getModule()->getDataLayout();
Value *UnderlyingVal = GetUnderlyingObject(Val, DL);
// If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
// inside InstructionDereferencesPointer either.
if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, DL, 1)) {
for (Instruction &I : *BB) {
if (InstructionDereferencesPointer(&I, UnderlyingVal)) {
NotNull = true;
break;
}
}
}
}
}
// If this is the entry block, we must be asking about an argument. The
// value is overdefined.
if (BB == &BB->getParent()->getEntryBlock()) {
assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
if (NotNull) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
} else {
Result.markOverdefined();
}
BBLV = Result;
return true;
}
// Loop over all of our predecessors, merging what we know from them into
// result.
bool EdgesMissing = false;
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
LVILatticeVal EdgeResult;
EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
if (EdgesMissing)
continue;
Result.mergeIn(EdgeResult, DL);
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred (non local).\n");
// If we previously determined that this is a pointer that can't be null
// then return that rather than giving up entirely.
if (NotNull) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
}
BBLV = Result;
return true;
}
}
if (EdgesMissing)
return false;
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined());
BBLV = Result;
return true;
}
bool LazyValueInfoCache::solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB) {
LVILatticeVal Result; // Start Undefined.
// Loop over all of our predecessors, merging what we know from them into
// result.
bool EdgesMissing = false;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *PhiBB = PN->getIncomingBlock(i);
Value *PhiVal = PN->getIncomingValue(i);
LVILatticeVal EdgeResult;
// Note that we can provide PN as the context value to getEdgeValue, even
// though the results will be cached, because PN is the value being used as
// the cache key in the caller.
EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult, PN);
if (EdgesMissing)
continue;
Result.mergeIn(EdgeResult, DL);
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred (local).\n");
BBLV = Result;
return true;
}
}
if (EdgesMissing)
return false;
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined() && "Possible PHI in entry block?");
BBLV = Result;
return true;
}
static bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
LVILatticeVal &Result,
bool isTrueDest = true);
// If we can determine a constraint on the value given conditions assumed by
// the program, intersect those constraints with BBLV
void LazyValueInfoCache::intersectAssumeBlockValueConstantRange(Value *Val,
LVILatticeVal &BBLV,
Instruction *BBI) {
BBI = BBI ? BBI : dyn_cast<Instruction>(Val);
if (!BBI)
return;
for (auto &AssumeVH : AC->assumptions()) {
if (!AssumeVH)
continue;
auto *I = cast<CallInst>(AssumeVH);
if (!isValidAssumeForContext(I, BBI, DT))
continue;
Value *C = I->getArgOperand(0);
if (ICmpInst *ICI = dyn_cast<ICmpInst>(C)) {
LVILatticeVal Result;
if (getValueFromFromCondition(Val, ICI, Result))
BBLV = intersect(BBLV, Result);
}
}
}
bool LazyValueInfoCache::solveBlockValueSelect(LVILatticeVal &BBLV,
SelectInst *SI, BasicBlock *BB) {
// Recurse on our inputs if needed
if (!hasBlockValue(SI->getTrueValue(), BB)) {
if (pushBlockValue(std::make_pair(BB, SI->getTrueValue())))
return false;
BBLV.markOverdefined();
return true;
}
LVILatticeVal TrueVal = getBlockValue(SI->getTrueValue(), BB);
// If we hit overdefined, don't ask more queries. We want to avoid poisoning
// extra slots in the table if we can.
if (TrueVal.isOverdefined()) {
BBLV.markOverdefined();
return true;
}
if (!hasBlockValue(SI->getFalseValue(), BB)) {
if (pushBlockValue(std::make_pair(BB, SI->getFalseValue())))
return false;
BBLV.markOverdefined();
return true;
}
LVILatticeVal FalseVal = getBlockValue(SI->getFalseValue(), BB);
// If we hit overdefined, don't ask more queries. We want to avoid poisoning
// extra slots in the table if we can.
if (FalseVal.isOverdefined()) {
BBLV.markOverdefined();
return true;
}
if (TrueVal.isConstantRange() && FalseVal.isConstantRange()) {
ConstantRange TrueCR = TrueVal.getConstantRange();
ConstantRange FalseCR = FalseVal.getConstantRange();
Value *LHS = nullptr;
Value *RHS = nullptr;
SelectPatternResult SPR = matchSelectPattern(SI, LHS, RHS);
// Is this a min specifically of our two inputs? (Avoid the risk of
// ValueTracking getting smarter looking back past our immediate inputs.)
if (SelectPatternResult::isMinOrMax(SPR.Flavor) &&
LHS == SI->getTrueValue() && RHS == SI->getFalseValue()) {
switch (SPR.Flavor) {
default:
llvm_unreachable("unexpected minmax type!");
case SPF_SMIN: /// Signed minimum
BBLV.markConstantRange(TrueCR.smin(FalseCR));
return true;
case SPF_UMIN: /// Unsigned minimum
BBLV.markConstantRange(TrueCR.umin(FalseCR));
return true;
case SPF_SMAX: /// Signed maximum
BBLV.markConstantRange(TrueCR.smax(FalseCR));
return true;
case SPF_UMAX: /// Unsigned maximum
BBLV.markConstantRange(TrueCR.umax(FalseCR));
return true;
};
}
// TODO: ABS, NABS from the SelectPatternResult
}
// Can we constrain the facts about the true and false values by using the
// condition itself? This shows up with idioms like e.g. select(a > 5, a, 5).
// TODO: We could potentially refine an overdefined true value above.
if (auto *ICI = dyn_cast<ICmpInst>(SI->getCondition())) {
LVILatticeVal TrueValTaken, FalseValTaken;
if (!getValueFromFromCondition(SI->getTrueValue(), ICI,
TrueValTaken, true))
TrueValTaken.markOverdefined();
if (!getValueFromFromCondition(SI->getFalseValue(), ICI,
FalseValTaken, false))
FalseValTaken.markOverdefined();
TrueVal = intersect(TrueVal, TrueValTaken);
FalseVal = intersect(FalseVal, FalseValTaken);
// Handle clamp idioms such as:
// %24 = constantrange<0, 17>
// %39 = icmp eq i32 %24, 0
// %40 = add i32 %24, -1
// %siv.next = select i1 %39, i32 16, i32 %40
// %siv.next = constantrange<0, 17> not <-1, 17>
// In general, this can handle any clamp idiom which tests the edge
// condition via an equality or inequality.
ICmpInst::Predicate Pred = ICI->getPredicate();
Value *A = ICI->getOperand(0);
if (ConstantInt *CIBase = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
auto addConstants = [](ConstantInt *A, ConstantInt *B) {
assert(A->getType() == B->getType());
return ConstantInt::get(A->getType(), A->getValue() + B->getValue());
};
// See if either input is A + C2, subject to the constraint from the
// condition that A != C when that input is used. We can assume that
// that input doesn't include C + C2.
ConstantInt *CIAdded;
switch (Pred) {
default: break;
case ICmpInst::ICMP_EQ:
if (match(SI->getFalseValue(), m_Add(m_Specific(A),
m_ConstantInt(CIAdded)))) {
auto ResNot = addConstants(CIBase, CIAdded);
FalseVal = intersect(FalseVal,
LVILatticeVal::getNot(ResNot));
}
break;
case ICmpInst::ICMP_NE:
if (match(SI->getTrueValue(), m_Add(m_Specific(A),
m_ConstantInt(CIAdded)))) {
auto ResNot = addConstants(CIBase, CIAdded);
TrueVal = intersect(TrueVal,
LVILatticeVal::getNot(ResNot));
}
break;
};
}
}
LVILatticeVal Result; // Start Undefined.
Result.mergeIn(TrueVal, DL);
Result.mergeIn(FalseVal, DL);
BBLV = Result;
return true;
}
bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI,
BasicBlock *BB) {
// Figure out the range of the LHS. If that fails, bail.
if (!hasBlockValue(BBI->getOperand(0), BB)) {
if (pushBlockValue(std::make_pair(BB, BBI->getOperand(0))))
return false;
BBLV.markOverdefined();
return true;
}
LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
intersectAssumeBlockValueConstantRange(BBI->getOperand(0), LHSVal, BBI);
if (!LHSVal.isConstantRange()) {
BBLV.markOverdefined();
return true;
}
ConstantRange LHSRange = LHSVal.getConstantRange();
ConstantRange RHSRange(1);
IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
if (isa<BinaryOperator>(BBI)) {
if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
RHSRange = ConstantRange(RHS->getValue());
} else {
BBLV.markOverdefined();
return true;
}
}
// NOTE: We're currently limited by the set of operations that ConstantRange
// can evaluate symbolically. Enhancing that set will allows us to analyze
// more definitions.
LVILatticeVal Result;
switch (BBI->getOpcode()) {
case Instruction::Add:
Result.markConstantRange(LHSRange.add(RHSRange));
break;
case Instruction::Sub:
Result.markConstantRange(LHSRange.sub(RHSRange));
break;
case Instruction::Mul:
Result.markConstantRange(LHSRange.multiply(RHSRange));
break;
case Instruction::UDiv:
Result.markConstantRange(LHSRange.udiv(RHSRange));
break;
case Instruction::Shl:
Result.markConstantRange(LHSRange.shl(RHSRange));
break;
case Instruction::LShr:
Result.markConstantRange(LHSRange.lshr(RHSRange));
break;
case Instruction::Trunc:
Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
break;
case Instruction::SExt:
Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
break;
case Instruction::ZExt:
Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
break;
case Instruction::BitCast:
Result.markConstantRange(LHSRange);
break;
case Instruction::And:
Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
break;
case Instruction::Or:
Result.markConstantRange(LHSRange.binaryOr(RHSRange));
break;
// Unhandled instructions are overdefined.
default:
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
Result.markOverdefined();
break;
}
BBLV = Result;
return true;
}
bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
LVILatticeVal &Result, bool isTrueDest) {
if (ICI && isa<Constant>(ICI->getOperand(1))) {
if (ICI->isEquality() && ICI->getOperand(0) == Val) {
// We know that V has the RHS constant if this is a true SETEQ or
// false SETNE.
if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
else
Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
return true;
}
// Recognize the range checking idiom that InstCombine produces.
// (X-C1) u< C2 --> [C1, C1+C2)
ConstantInt *NegOffset = nullptr;
if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
match(ICI->getOperand(0), m_Add(m_Specific(Val),
m_ConstantInt(NegOffset)));
ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
// Calculate the range of values that are allowed by the comparison
ConstantRange CmpRange(CI->getValue());
ConstantRange TrueValues =
ConstantRange::makeAllowedICmpRegion(ICI->getPredicate(), CmpRange);
if (NegOffset) // Apply the offset from above.
TrueValues = TrueValues.subtract(NegOffset->getValue());
// If we're interested in the false dest, invert the condition.
if (!isTrueDest) TrueValues = TrueValues.inverse();
Result = LVILatticeVal::getRange(std::move(TrueValues));
return true;
}
}
return false;
}
/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
/// Val is not constrained on the edge. Result is unspecified if return value
/// is false.
static bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
BasicBlock *BBTo, LVILatticeVal &Result) {
// TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
// know that v != 0.
if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
// If this is a conditional branch and only one successor goes to BBTo, then
// we may be able to infer something from the condition.
if (BI->isConditional() &&
BI->getSuccessor(0) != BI->getSuccessor(1)) {
bool isTrueDest = BI->getSuccessor(0) == BBTo;
assert(BI->getSuccessor(!isTrueDest) == BBTo &&
"BBTo isn't a successor of BBFrom");
// If V is the condition of the branch itself, then we know exactly what
// it is.
if (BI->getCondition() == Val) {
Result = LVILatticeVal::get(ConstantInt::get(
Type::getInt1Ty(Val->getContext()), isTrueDest));
return true;
}
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
if (getValueFromFromCondition(Val, ICI, Result, isTrueDest))
return true;
}
}
// If the edge was formed by a switch on the value, then we may know exactly
// what it is.
if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
if (SI->getCondition() != Val)
return false;
bool DefaultCase = SI->getDefaultDest() == BBTo;
unsigned BitWidth = Val->getType()->getIntegerBitWidth();
ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
for (SwitchInst::CaseIt i : SI->cases()) {
ConstantRange EdgeVal(i.getCaseValue()->getValue());
if (DefaultCase) {
// It is possible that the default destination is the destination of
// some cases. There is no need to perform difference for those cases.
if (i.getCaseSuccessor() != BBTo)
EdgesVals = EdgesVals.difference(EdgeVal);
} else if (i.getCaseSuccessor() == BBTo)
EdgesVals = EdgesVals.unionWith(EdgeVal);
}
Result = LVILatticeVal::getRange(std::move(EdgesVals));
return true;
}
return false;
}
/// \brief Compute the value of Val on the edge BBFrom -> BBTo or the value at
/// the basic block if the edge does not constrain Val.
bool LazyValueInfoCache::getEdgeValue(Value *Val, BasicBlock *BBFrom,
BasicBlock *BBTo, LVILatticeVal &Result,
Instruction *CxtI) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val)) {
Result = LVILatticeVal::get(VC);
return true;
}
LVILatticeVal LocalResult;
if (!getEdgeValueLocal(Val, BBFrom, BBTo, LocalResult))
// If we couldn't constrain the value on the edge, LocalResult doesn't
// provide any information.
LocalResult.markOverdefined();
if (hasSingleValue(LocalResult)) {
// Can't get any more precise here
Result = LocalResult;
return true;
}
if (!hasBlockValue(Val, BBFrom)) {
if (pushBlockValue(std::make_pair(BBFrom, Val)))
return false;
// No new information.
Result = LocalResult;
return true;
}
// Try to intersect ranges of the BB and the constraint on the edge.
LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
intersectAssumeBlockValueConstantRange(Val, InBlock, BBFrom->getTerminator());
// We can use the context instruction (generically the ultimate instruction
// the calling pass is trying to simplify) here, even though the result of
// this function is generally cached when called from the solve* functions
// (and that cached result might be used with queries using a different
// context instruction), because when this function is called from the solve*
// functions, the context instruction is not provided. When called from
// LazyValueInfoCache::getValueOnEdge, the context instruction is provided,
// but then the result is not cached.
intersectAssumeBlockValueConstantRange(Val, InBlock, CxtI);
Result = intersect(LocalResult, InBlock);
return true;
}
LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB,
Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
<< BB->getName() << "'\n");
assert(BlockValueStack.empty() && BlockValueSet.empty());
if (!hasBlockValue(V, BB)) {
pushBlockValue(std::make_pair(BB, V));
solve();
}
LVILatticeVal Result = getBlockValue(V, BB);
intersectAssumeBlockValueConstantRange(V, Result, CxtI);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoCache::getValueAt(Value *V, Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting value " << *V << " at '"
<< CxtI->getName() << "'\n");
if (auto *C = dyn_cast<Constant>(V))
return LVILatticeVal::get(C);
LVILatticeVal Result = LVILatticeVal::getOverdefined();
if (auto *I = dyn_cast<Instruction>(V))
Result = getFromRangeMetadata(I);
intersectAssumeBlockValueConstantRange(V, Result, CxtI);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoCache::
getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB,
Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
<< FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
LVILatticeVal Result;
if (!getEdgeValue(V, FromBB, ToBB, Result, CxtI)) {
solve();
bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result, CxtI);
(void)WasFastQuery;
assert(WasFastQuery && "More work to do after problem solved?");
}
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
void LazyValueInfoCache::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
// When an edge in the graph has been threaded, values that we could not
// determine a value for before (i.e. were marked overdefined) may be
// possible to solve now. We do NOT try to proactively update these values.
// Instead, we clear their entries from the cache, and allow lazy updating to
// recompute them when needed.
// The updating process is fairly simple: we need to drop cached info
// for all values that were marked overdefined in OldSucc, and for those same
// values in any successor of OldSucc (except NewSucc) in which they were
// also marked overdefined.
std::vector<BasicBlock*> worklist;
worklist.push_back(OldSucc);
auto I = OverDefinedCache.find(OldSucc);
if (I == OverDefinedCache.end())
return; // Nothing to process here.
SmallVector<Value *, 4> ValsToClear(I->second.begin(), I->second.end());
// Use a worklist to perform a depth-first search of OldSucc's successors.
// NOTE: We do not need a visited list since any blocks we have already
// visited will have had their overdefined markers cleared already, and we
// thus won't loop to their successors.
while (!worklist.empty()) {
BasicBlock *ToUpdate = worklist.back();
worklist.pop_back();
// Skip blocks only accessible through NewSucc.
if (ToUpdate == NewSucc) continue;
bool changed = false;
for (Value *V : ValsToClear) {
// If a value was marked overdefined in OldSucc, and is here too...
auto OI = OverDefinedCache.find(ToUpdate);
if (OI == OverDefinedCache.end())
continue;
SmallPtrSetImpl<Value *> &ValueSet = OI->second;
if (!ValueSet.count(V))
continue;
ValueSet.erase(V);
if (ValueSet.empty())
OverDefinedCache.erase(OI);
// If we removed anything, then we potentially need to update
// blocks successors too.
changed = true;
}
if (!changed) continue;
worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
}
}
//===----------------------------------------------------------------------===//
// LazyValueInfo Impl
//===----------------------------------------------------------------------===//
/// This lazily constructs the LazyValueInfoCache.
static LazyValueInfoCache &getCache(void *&PImpl, AssumptionCache *AC,
const DataLayout *DL,
DominatorTree *DT = nullptr) {
if (!PImpl) {
assert(DL && "getCache() called with a null DataLayout");
PImpl = new LazyValueInfoCache(AC, *DL, DT);
}
return *static_cast<LazyValueInfoCache*>(PImpl);
}
bool LazyValueInfo::runOnFunction(Function &F) {
AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
const DataLayout &DL = F.getParent()->getDataLayout();
DominatorTreeWrapperPass *DTWP =
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
DT = DTWP ? &DTWP->getDomTree() : nullptr;
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
if (PImpl)
getCache(PImpl, AC, &DL, DT).clear();
// Fully lazy.
return false;
}
void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}
void LazyValueInfo::releaseMemory() {
// If the cache was allocated, free it.
if (PImpl) {
delete &getCache(PImpl, AC, nullptr);
PImpl = nullptr;
}
}
Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB,
Instruction *CxtI) {
const DataLayout &DL = BB->getModule()->getDataLayout();
LVILatticeVal Result =
getCache(PImpl, AC, &DL, DT).getValueInBlock(V, BB, CxtI);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
ConstantRange CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
}
return nullptr;
}
/// Determine whether the specified value is known to be a
/// constant on the specified edge. Return null if not.
Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
BasicBlock *ToBB,
Instruction *CxtI) {
const DataLayout &DL = FromBB->getModule()->getDataLayout();
LVILatticeVal Result =
getCache(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
ConstantRange CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
}
return nullptr;
}
static LazyValueInfo::Tristate getPredicateResult(unsigned Pred, Constant *C,
LVILatticeVal &Result,
const DataLayout &DL,
TargetLibraryInfo *TLI) {
// If we know the value is a constant, evaluate the conditional.
Constant *Res = nullptr;
if (Result.isConstant()) {
Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, DL,
TLI);
if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
return ResCI->isZero() ? LazyValueInfo::False : LazyValueInfo::True;
return LazyValueInfo::Unknown;
}
if (Result.isConstantRange()) {
ConstantInt *CI = dyn_cast<ConstantInt>(C);
if (!CI) return LazyValueInfo::Unknown;
ConstantRange CR = Result.getConstantRange();
if (Pred == ICmpInst::ICMP_EQ) {
if (!CR.contains(CI->getValue()))
return LazyValueInfo::False;
if (CR.isSingleElement() && CR.contains(CI->getValue()))
return LazyValueInfo::True;
} else if (Pred == ICmpInst::ICMP_NE) {
if (!CR.contains(CI->getValue()))
return LazyValueInfo::True;
if (CR.isSingleElement() && CR.contains(CI->getValue()))
return LazyValueInfo::False;
}
// Handle more complex predicates.
ConstantRange TrueValues =
ICmpInst::makeConstantRange((ICmpInst::Predicate)Pred, CI->getValue());
if (TrueValues.contains(CR))
return LazyValueInfo::True;
if (TrueValues.inverse().contains(CR))
return LazyValueInfo::False;
return LazyValueInfo::Unknown;
}
if (Result.isNotConstant()) {
// If this is an equality comparison, we can try to fold it knowing that
// "V != C1".
if (Pred == ICmpInst::ICMP_EQ) {
// !C1 == C -> false iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Result.getNotConstant(), C, DL,
TLI);
if (Res->isNullValue())
return LazyValueInfo::False;
} else if (Pred == ICmpInst::ICMP_NE) {
// !C1 != C -> true iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Result.getNotConstant(), C, DL,
TLI);
if (Res->isNullValue())
return LazyValueInfo::True;
}
return LazyValueInfo::Unknown;
}
return LazyValueInfo::Unknown;
}
/// Determine whether the specified value comparison with a constant is known to
/// be true or false on the specified CFG edge. Pred is a CmpInst predicate.
LazyValueInfo::Tristate
LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
BasicBlock *FromBB, BasicBlock *ToBB,
Instruction *CxtI) {
const DataLayout &DL = FromBB->getModule()->getDataLayout();
LVILatticeVal Result =
getCache(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
return getPredicateResult(Pred, C, Result, DL, TLI);
}
LazyValueInfo::Tristate
LazyValueInfo::getPredicateAt(unsigned Pred, Value *V, Constant *C,
Instruction *CxtI) {
const DataLayout &DL = CxtI->getModule()->getDataLayout();
LVILatticeVal Result = getCache(PImpl, AC, &DL, DT).getValueAt(V, CxtI);
Tristate Ret = getPredicateResult(Pred, C, Result, DL, TLI);
if (Ret != Unknown)
return Ret;
// Note: The following bit of code is somewhat distinct from the rest of LVI;
// LVI as a whole tries to compute a lattice value which is conservatively
// correct at a given location. In this case, we have a predicate which we
// weren't able to prove about the merged result, and we're pushing that
// predicate back along each incoming edge to see if we can prove it
// separately for each input. As a motivating example, consider:
// bb1:
// %v1 = ... ; constantrange<1, 5>
// br label %merge
// bb2:
// %v2 = ... ; constantrange<10, 20>
// br label %merge
// merge:
// %phi = phi [%v1, %v2] ; constantrange<1,20>
// %pred = icmp eq i32 %phi, 8
// We can't tell from the lattice value for '%phi' that '%pred' is false
// along each path, but by checking the predicate over each input separately,
// we can.
// We limit the search to one step backwards from the current BB and value.
// We could consider extending this to search further backwards through the
// CFG and/or value graph, but there are non-obvious compile time vs quality
// tradeoffs.
if (CxtI) {
BasicBlock *BB = CxtI->getParent();
// Function entry or an unreachable block. Bail to avoid confusing
// analysis below.
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
if (PI == PE)
return Unknown;
// If V is a PHI node in the same block as the context, we need to ask
// questions about the predicate as applied to the incoming value along
// each edge. This is useful for eliminating cases where the predicate is
// known along all incoming edges.
if (auto *PHI = dyn_cast<PHINode>(V))
if (PHI->getParent() == BB) {
Tristate Baseline = Unknown;
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i < e; i++) {
Value *Incoming = PHI->getIncomingValue(i);
BasicBlock *PredBB = PHI->getIncomingBlock(i);
// Note that PredBB may be BB itself.
Tristate Result = getPredicateOnEdge(Pred, Incoming, C, PredBB, BB,
CxtI);
// Keep going as long as we've seen a consistent known result for
// all inputs.
Baseline = (i == 0) ? Result /* First iteration */
: (Baseline == Result ? Baseline : Unknown); /* All others */
if (Baseline == Unknown)
break;
}
if (Baseline != Unknown)
return Baseline;
}
// For a comparison where the V is outside this block, it's possible
// that we've branched on it before. Look to see if the value is known
// on all incoming edges.
if (!isa<Instruction>(V) ||
cast<Instruction>(V)->getParent() != BB) {
// For predecessor edge, determine if the comparison is true or false
// on that edge. If they're all true or all false, we can conclude
// the value of the comparison in this block.
Tristate Baseline = getPredicateOnEdge(Pred, V, C, *PI, BB, CxtI);
if (Baseline != Unknown) {
// Check that all remaining incoming values match the first one.
while (++PI != PE) {
Tristate Ret = getPredicateOnEdge(Pred, V, C, *PI, BB, CxtI);
if (Ret != Baseline) break;
}
// If we terminated early, then one of the values didn't match.
if (PI == PE) {
return Baseline;
}
}
}
}
return Unknown;
}
void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
if (PImpl) {
const DataLayout &DL = PredBB->getModule()->getDataLayout();
getCache(PImpl, AC, &DL, DT).threadEdge(PredBB, OldSucc, NewSucc);
}
}
void LazyValueInfo::eraseBlock(BasicBlock *BB) {
if (PImpl) {
const DataLayout &DL = BB->getModule()->getDataLayout();
getCache(PImpl, AC, &DL, DT).eraseBlock(BB);
}
}
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