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-rw-r--r--llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp74
1 files changed, 58 insertions, 16 deletions
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index c43dd818e8a..d6427b2e955 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -70,6 +70,7 @@ static void
deleteDeadInstruction(Instruction *I, BasicBlock::iterator *BBI,
MemoryDependenceResults &MD, const TargetLibraryInfo &TLI,
InstOverlapIntervalsTy &IOL,
+ DenseMap<Instruction*, size_t> *InstrOrdering,
SmallSetVector<Value *, 16> *ValueSet = nullptr) {
SmallVector<Instruction*, 32> NowDeadInsts;
@@ -102,15 +103,14 @@ deleteDeadInstruction(Instruction *I, BasicBlock::iterator *BBI,
NowDeadInsts.push_back(OpI);
}
+ if (ValueSet) ValueSet->remove(DeadInst);
+ InstrOrdering->erase(DeadInst);
+ IOL.erase(DeadInst);
if (NewIter == DeadInst->getIterator())
NewIter = DeadInst->eraseFromParent();
else
DeadInst->eraseFromParent();
-
- IOL.erase(DeadInst);
-
- if (ValueSet) ValueSet->remove(DeadInst);
} while (!NowDeadInsts.empty());
*BBI = NewIter;
}
@@ -590,7 +590,8 @@ static void findUnconditionalPreds(SmallVectorImpl<BasicBlock *> &Blocks,
static bool handleFree(CallInst *F, AliasAnalysis *AA,
MemoryDependenceResults *MD, DominatorTree *DT,
const TargetLibraryInfo *TLI,
- InstOverlapIntervalsTy &IOL) {
+ InstOverlapIntervalsTy &IOL,
+ DenseMap<Instruction*, size_t> *InstrOrdering) {
bool MadeChange = false;
MemoryLocation Loc = MemoryLocation(F->getOperand(0));
@@ -622,7 +623,7 @@ static bool handleFree(CallInst *F, AliasAnalysis *AA,
// DCE instructions only used to calculate that store.
BasicBlock::iterator BBI(Dependency);
- deleteDeadInstruction(Dependency, &BBI, *MD, *TLI, IOL);
+ deleteDeadInstruction(Dependency, &BBI, *MD, *TLI, IOL, InstrOrdering);
++NumFastStores;
MadeChange = true;
@@ -678,7 +679,8 @@ static void removeAccessedObjects(const MemoryLocation &LoadedLoc,
static bool handleEndBlock(BasicBlock &BB, AliasAnalysis *AA,
MemoryDependenceResults *MD,
const TargetLibraryInfo *TLI,
- InstOverlapIntervalsTy &IOL) {
+ InstOverlapIntervalsTy &IOL,
+ DenseMap<Instruction*, size_t> *InstrOrdering) {
bool MadeChange = false;
// Keep track of all of the stack objects that are dead at the end of the
@@ -737,7 +739,7 @@ static bool handleEndBlock(BasicBlock &BB, AliasAnalysis *AA,
dbgs() << '\n');
// DCE instructions only used to calculate that store.
- deleteDeadInstruction(Dead, &BBI, *MD, *TLI, IOL, &DeadStackObjects);
+ deleteDeadInstruction(Dead, &BBI, *MD, *TLI, IOL, InstrOrdering, &DeadStackObjects);
++NumFastStores;
MadeChange = true;
continue;
@@ -748,7 +750,7 @@ static bool handleEndBlock(BasicBlock &BB, AliasAnalysis *AA,
if (isInstructionTriviallyDead(&*BBI, TLI)) {
DEBUG(dbgs() << "DSE: Removing trivially dead instruction:\n DEAD: "
<< *&*BBI << '\n');
- deleteDeadInstruction(&*BBI, &BBI, *MD, *TLI, IOL, &DeadStackObjects);
+ deleteDeadInstruction(&*BBI, &BBI, *MD, *TLI, IOL, InstrOrdering, &DeadStackObjects);
++NumFastOther;
MadeChange = true;
continue;
@@ -947,7 +949,8 @@ static bool eliminateNoopStore(Instruction *Inst, BasicBlock::iterator &BBI,
AliasAnalysis *AA, MemoryDependenceResults *MD,
const DataLayout &DL,
const TargetLibraryInfo *TLI,
- InstOverlapIntervalsTy &IOL) {
+ InstOverlapIntervalsTy &IOL,
+ DenseMap<Instruction*, size_t> *InstrOrdering) {
// Must be a store instruction.
StoreInst *SI = dyn_cast<StoreInst>(Inst);
if (!SI)
@@ -962,7 +965,7 @@ static bool eliminateNoopStore(Instruction *Inst, BasicBlock::iterator &BBI,
DEBUG(dbgs() << "DSE: Remove Store Of Load from same pointer:\n LOAD: "
<< *DepLoad << "\n STORE: " << *SI << '\n');
- deleteDeadInstruction(SI, &BBI, *MD, *TLI, IOL);
+ deleteDeadInstruction(SI, &BBI, *MD, *TLI, IOL, InstrOrdering);
++NumRedundantStores;
return true;
}
@@ -980,7 +983,7 @@ static bool eliminateNoopStore(Instruction *Inst, BasicBlock::iterator &BBI,
dbgs() << "DSE: Remove null store to the calloc'ed object:\n DEAD: "
<< *Inst << "\n OBJECT: " << *UnderlyingPointer << '\n');
- deleteDeadInstruction(SI, &BBI, *MD, *TLI, IOL);
+ deleteDeadInstruction(SI, &BBI, *MD, *TLI, IOL, InstrOrdering);
++NumRedundantStores;
return true;
}
@@ -994,6 +997,12 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
const DataLayout &DL = BB.getModule()->getDataLayout();
bool MadeChange = false;
+ // FIXME: Maybe change this to use some abstraction like OrderedBasicBlock?
+ // The current OrderedBasicBlock can't deal with mutation at the moment.
+ size_t LastThrowingInstIndex = 0;
+ DenseMap<Instruction*, size_t> InstrOrdering;
+ size_t InstrIndex = 1;
+
// A map of interval maps representing partially-overwritten value parts.
InstOverlapIntervalsTy IOL;
@@ -1001,7 +1010,7 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
for (BasicBlock::iterator BBI = BB.begin(), BBE = BB.end(); BBI != BBE; ) {
// Handle 'free' calls specially.
if (CallInst *F = isFreeCall(&*BBI, TLI)) {
- MadeChange |= handleFree(F, AA, MD, DT, TLI, IOL);
+ MadeChange |= handleFree(F, AA, MD, DT, TLI, IOL, &InstrOrdering);
// Increment BBI after handleFree has potentially deleted instructions.
// This ensures we maintain a valid iterator.
++BBI;
@@ -1010,12 +1019,19 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
Instruction *Inst = &*BBI++;
+ size_t CurInstNumber = InstrIndex++;
+ InstrOrdering.insert(std::make_pair(Inst, CurInstNumber));
+ if (Inst->mayThrow()) {
+ LastThrowingInstIndex = CurInstNumber;
+ continue;
+ }
+
// Check to see if Inst writes to memory. If not, continue.
if (!hasMemoryWrite(Inst, *TLI))
continue;
// eliminateNoopStore will update in iterator, if necessary.
- if (eliminateNoopStore(Inst, BBI, AA, MD, DL, TLI, IOL)) {
+ if (eliminateNoopStore(Inst, BBI, AA, MD, DL, TLI, IOL, &InstrOrdering)) {
MadeChange = true;
continue;
}
@@ -1049,6 +1065,31 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
if (!DepLoc.Ptr)
break;
+ // Make sure we don't look past a call which might throw. This is an
+ // issue because MemoryDependenceAnalysis works in the wrong direction:
+ // it finds instructions which dominate the current instruction, rather than
+ // instructions which are post-dominated by the current instruction.
+ //
+ // If the underlying object is a non-escaping memory allocation, any store
+ // to it is dead along the unwind edge. Otherwise, we need to preserve
+ // the store.
+ size_t DepIndex = InstrOrdering.lookup(DepWrite);
+ assert(DepIndex && "Unexpected instruction");
+ if (DepIndex <= LastThrowingInstIndex) {
+ const Value* Underlying = GetUnderlyingObject(DepLoc.Ptr, DL);
+ bool IsStoreDeadOnUnwind = isa<AllocaInst>(Underlying);
+ if (!IsStoreDeadOnUnwind) {
+ // We're looking for a call to an allocation function
+ // where the allocation doesn't escape before the last
+ // throwing instruction; PointerMayBeCaptured
+ // reasonably fast approximation.
+ IsStoreDeadOnUnwind = isAllocLikeFn(Underlying, TLI) &&
+ !PointerMayBeCaptured(Underlying, false, true);
+ }
+ if (!IsStoreDeadOnUnwind)
+ break;
+ }
+
// If we find a write that is a) removable (i.e., non-volatile), b) is
// completely obliterated by the store to 'Loc', and c) which we know that
// 'Inst' doesn't load from, then we can remove it.
@@ -1063,7 +1104,7 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
<< *DepWrite << "\n KILLER: " << *Inst << '\n');
// Delete the store and now-dead instructions that feed it.
- deleteDeadInstruction(DepWrite, &BBI, *MD, *TLI, IOL);
+ deleteDeadInstruction(DepWrite, &BBI, *MD, *TLI, IOL, &InstrOrdering);
++NumFastStores;
MadeChange = true;
@@ -1109,7 +1150,7 @@ static bool eliminateDeadStores(BasicBlock &BB, AliasAnalysis *AA,
// If this block ends in a return, unwind, or unreachable, all allocas are
// dead at its end, which means stores to them are also dead.
if (BB.getTerminator()->getNumSuccessors() == 0)
- MadeChange |= handleEndBlock(BB, AA, MD, TLI, IOL);
+ MadeChange |= handleEndBlock(BB, AA, MD, TLI, IOL, &InstrOrdering);
return MadeChange;
}
@@ -1123,6 +1164,7 @@ static bool eliminateDeadStores(Function &F, AliasAnalysis *AA,
// cycles that will confuse alias analysis.
if (DT->isReachableFromEntry(&BB))
MadeChange |= eliminateDeadStores(BB, AA, MD, DT, TLI);
+
return MadeChange;
}
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