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[DeadStoreElimination] Remove dead zero store to calloc initialized memory
This change allows dead store elimination to remove zero and null stores into memory freshly allocated with calloc-like function. Differential Revision: http://reviews.llvm.org/D13021 llvm-svn: 248374
This commit is contained in:
Igor Laevsky
parent
19c3231029
commit
fd0eac2496
@ -78,7 +78,7 @@ namespace {
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}
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bool runOnBasicBlock(BasicBlock &BB);
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bool MemoryIsNotModifiedBetween(LoadInst *LI, StoreInst *SI);
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bool MemoryIsNotModifiedBetween(Instruction *FirstI, Instruction *SecondI);
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bool HandleFree(CallInst *F);
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bool handleEndBlock(BasicBlock &BB);
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void RemoveAccessedObjects(const MemoryLocation &LoadedLoc,
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@ -483,6 +483,7 @@ static bool isPossibleSelfRead(Instruction *Inst,
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//===----------------------------------------------------------------------===//
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bool DSE::runOnBasicBlock(BasicBlock &BB) {
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const DataLayout &DL = BB.getModule()->getDataLayout();
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bool MadeChange = false;
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// Do a top-down walk on the BB.
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@ -502,6 +503,22 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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// If we're storing the same value back to a pointer that we just
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// loaded from, then the store can be removed.
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if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
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auto RemoveDeadInstAndUpdateBBI = [&](Instruction *DeadInst) {
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// DeleteDeadInstruction can delete the current instruction. Save BBI
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// in case we need it.
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WeakVH NextInst(BBI);
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DeleteDeadInstruction(DeadInst, *MD, *TLI);
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if (!NextInst) // Next instruction deleted.
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BBI = BB.begin();
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else if (BBI != BB.begin()) // Revisit this instruction if possible.
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--BBI;
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++NumRedundantStores;
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MadeChange = true;
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};
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if (LoadInst *DepLoad = dyn_cast<LoadInst>(SI->getValueOperand())) {
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if (SI->getPointerOperand() == DepLoad->getPointerOperand() &&
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isRemovable(SI) &&
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@ -510,18 +527,26 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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DEBUG(dbgs() << "DSE: Remove Store Of Load from same pointer:\n "
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<< "LOAD: " << *DepLoad << "\n STORE: " << *SI << '\n');
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// DeleteDeadInstruction can delete the current instruction. Save BBI
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// in case we need it.
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WeakVH NextInst(BBI);
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RemoveDeadInstAndUpdateBBI(SI);
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continue;
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}
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}
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DeleteDeadInstruction(SI, *MD, *TLI);
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// Remove null stores into the calloc'ed objects
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Constant *StoredConstant = dyn_cast<Constant>(SI->getValueOperand());
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if (!NextInst) // Next instruction deleted.
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BBI = BB.begin();
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else if (BBI != BB.begin()) // Revisit this instruction if possible.
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--BBI;
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++NumRedundantStores;
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MadeChange = true;
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if (StoredConstant && StoredConstant->isNullValue() &&
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isRemovable(SI)) {
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Instruction *UnderlyingPointer = dyn_cast<Instruction>(
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GetUnderlyingObject(SI->getPointerOperand(), DL));
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if (UnderlyingPointer && isCallocLikeFn(UnderlyingPointer, TLI) &&
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MemoryIsNotModifiedBetween(UnderlyingPointer, SI)) {
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DEBUG(dbgs()
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<< "DSE: Remove null store to the calloc'ed object:\n DEAD: "
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<< *Inst << "\n OBJECT: " << *UnderlyingPointer << '\n');
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RemoveDeadInstAndUpdateBBI(SI);
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continue;
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}
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}
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@ -561,7 +586,6 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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if (isRemovable(DepWrite) &&
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!isPossibleSelfRead(Inst, Loc, DepWrite, *TLI, *AA)) {
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int64_t InstWriteOffset, DepWriteOffset;
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const DataLayout &DL = BB.getModule()->getDataLayout();
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OverwriteResult OR =
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isOverwrite(Loc, DepLoc, DL, *TLI, DepWriteOffset, InstWriteOffset);
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if (OR == OverwriteComplete) {
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@ -633,52 +657,53 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
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return MadeChange;
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}
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/// Returns true if the memory which is accessed by the store instruction is not
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/// modified between the load and the store instruction.
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/// Precondition: The store instruction must be dominated by the load
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/// Returns true if the memory which is accessed by the second instruction is not
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/// modified between the first and the second instruction.
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/// Precondition: Second instruction must be dominated by the first
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/// instruction.
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bool DSE::MemoryIsNotModifiedBetween(LoadInst *LI, StoreInst *SI) {
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bool DSE::MemoryIsNotModifiedBetween(Instruction *FirstI,
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Instruction *SecondI) {
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SmallVector<BasicBlock *, 16> WorkList;
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SmallPtrSet<BasicBlock *, 8> Visited;
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BasicBlock::iterator LoadBBI(LI);
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++LoadBBI;
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BasicBlock::iterator StoreBBI(SI);
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BasicBlock *LoadBB = LI->getParent();
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BasicBlock *StoreBB = SI->getParent();
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MemoryLocation StoreLoc = MemoryLocation::get(SI);
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BasicBlock::iterator FirstBBI(FirstI);
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++FirstBBI;
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BasicBlock::iterator SecondBBI(SecondI);
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BasicBlock *FirstBB = FirstI->getParent();
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BasicBlock *SecondBB = SecondI->getParent();
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MemoryLocation MemLoc = MemoryLocation::get(SecondI);
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// Start checking the store-block.
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WorkList.push_back(StoreBB);
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WorkList.push_back(SecondBB);
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bool isFirstBlock = true;
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// Check all blocks going backward until we reach the load-block.
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while (!WorkList.empty()) {
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BasicBlock *B = WorkList.pop_back_val();
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// Ignore instructions before LI if this is the LoadBB.
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BasicBlock::iterator BI = (B == LoadBB ? LoadBBI : B->begin());
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// Ignore instructions before LI if this is the FirstBB.
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BasicBlock::iterator BI = (B == FirstBB ? FirstBBI : B->begin());
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BasicBlock::iterator EI;
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if (isFirstBlock) {
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// Ignore instructions after SI if this is the first visit of StoreBB.
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assert(B == StoreBB && "first block is not the store block");
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EI = StoreBBI;
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// Ignore instructions after SI if this is the first visit of SecondBB.
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assert(B == SecondBB && "first block is not the store block");
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EI = SecondBBI;
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isFirstBlock = false;
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} else {
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// It's not StoreBB or (in case of a loop) the second visit of StoreBB.
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// It's not SecondBB or (in case of a loop) the second visit of SecondBB.
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// In this case we also have to look at instructions after SI.
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EI = B->end();
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}
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for (; BI != EI; ++BI) {
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Instruction *I = BI;
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if (I->mayWriteToMemory() && I != SI) {
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auto Res = AA->getModRefInfo(I, StoreLoc);
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if (I->mayWriteToMemory() && I != SecondI) {
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auto Res = AA->getModRefInfo(I, MemLoc);
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if (Res != MRI_NoModRef)
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return false;
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}
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}
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if (B != LoadBB) {
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assert(B != &LoadBB->getParent()->getEntryBlock() &&
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if (B != FirstBB) {
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assert(B != &FirstBB->getParent()->getEntryBlock() &&
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"Should not hit the entry block because SI must be dominated by LI");
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for (auto PredI = pred_begin(B), PE = pred_end(B); PredI != PE; ++PredI) {
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if (!Visited.insert(*PredI).second)
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65
test/Transforms/DeadStoreElimination/calloc-store.ll
Normal file
65
test/Transforms/DeadStoreElimination/calloc-store.ll
Normal file
@ -0,0 +1,65 @@
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; RUN: opt < %s -basicaa -dse -S | FileCheck %s
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declare noalias i8* @calloc(i64, i64)
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define i32* @test1() {
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; CHECK-LABEL: test1
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%1 = tail call noalias i8* @calloc(i64 1, i64 4)
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%2 = bitcast i8* %1 to i32*
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; This store is dead and should be removed
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store i32 0, i32* %2, align 4
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; CHECK-NOT: store i32 0, i32* %2, align 4
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ret i32* %2
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}
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define i32* @test2() {
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; CHECK-LABEL: test2
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%1 = tail call noalias i8* @calloc(i64 1, i64 4)
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%2 = bitcast i8* %1 to i32*
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%3 = getelementptr i32, i32* %2, i32 5
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store i32 0, i32* %3, align 4
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; CHECK-NOT: store i32 0, i32* %2, align 4
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ret i32* %2
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}
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define i32* @test3(i32 *%arg) {
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; CHECK-LABEL: test3
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store i32 0, i32* %arg, align 4
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; CHECK: store i32 0, i32* %arg, align 4
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ret i32* %arg
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}
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declare void @clobber_memory(i8*)
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define i8* @test4() {
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; CHECK-LABEL: test4
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%1 = tail call noalias i8* @calloc(i64 1, i64 4)
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call void @clobber_memory(i8* %1)
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store i8 0, i8* %1, align 4
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; CHECK: store i8 0, i8* %1, align 4
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ret i8* %1
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}
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define i32* @test5() {
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; CHECK-LABEL: test5
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%1 = tail call noalias i8* @calloc(i64 1, i64 4)
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%2 = bitcast i8* %1 to i32*
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store volatile i32 0, i32* %2, align 4
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; CHECK: store volatile i32 0, i32* %2, align 4
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ret i32* %2
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}
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define i8* @test6() {
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; CHECK-LABEL: test6
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%1 = tail call noalias i8* @calloc(i64 1, i64 4)
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store i8 5, i8* %1, align 4
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; CHECK: store i8 5, i8* %1, align 4
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ret i8* %1
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}
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define i8* @test7(i8 %arg) {
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; CHECK-LABEL: test7
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%1 = tail call noalias i8* @calloc(i64 1, i64 4)
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store i8 %arg, i8* %1, align 4
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; CHECK: store i8 %arg, i8* %1, align 4
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ret i8* %1
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}
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