[llvm-commits] [llvm] r143808 - in /llvm/trunk: lib/Transforms/Scalar/DeadStoreElimination.cpp test/Transforms/DeadStoreElimination/free.ll
Nick Lewycky
nicholas at mxc.ca
Sat Nov 5 03:48:42 PDT 2011
Author: nicholas
Date: Sat Nov 5 05:48:42 2011
New Revision: 143808
URL: http://llvm.org/viewvc/llvm-project?rev=143808&view=rev
Log:
Do simple cross-block DSE when we encounter a free statement. Fixes PR11240.
Modified:
llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
llvm/trunk/test/Transforms/DeadStoreElimination/free.ll
Modified: llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp?rev=143808&r1=143807&r2=143808&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/DeadStoreElimination.cpp Sat Nov 5 05:48:42 2011
@@ -34,6 +34,7 @@
#include "llvm/Support/Debug.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/STLExtras.h"
using namespace llvm;
STATISTIC(NumFastStores, "Number of stores deleted");
@@ -43,25 +44,26 @@
struct DSE : public FunctionPass {
AliasAnalysis *AA;
MemoryDependenceAnalysis *MD;
+ DominatorTree *DT;
static char ID; // Pass identification, replacement for typeid
- DSE() : FunctionPass(ID), AA(0), MD(0) {
+ DSE() : FunctionPass(ID), AA(0), MD(0), DT(0) {
initializeDSEPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F) {
AA = &getAnalysis<AliasAnalysis>();
MD = &getAnalysis<MemoryDependenceAnalysis>();
- DominatorTree &DT = getAnalysis<DominatorTree>();
+ DT = &getAnalysis<DominatorTree>();
bool Changed = false;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
// Only check non-dead blocks. Dead blocks may have strange pointer
// cycles that will confuse alias analysis.
- if (DT.isReachableFromEntry(I))
+ if (DT->isReachableFromEntry(I))
Changed |= runOnBasicBlock(*I);
- AA = 0; MD = 0;
+ AA = 0; MD = 0; DT = 0;
return Changed;
}
@@ -549,37 +551,66 @@
return MadeChange;
}
+/// Find all blocks that will unconditionally lead to the block BB and append
+/// them to F.
+static void FindUnconditionalPreds(SmallVectorImpl<BasicBlock *> &Blocks,
+ BasicBlock *BB, DominatorTree *DT) {
+ for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
+ BasicBlock *Pred = *I;
+ TerminatorInst *PredTI = Pred->getTerminator();
+ if (PredTI->getNumSuccessors() != 1)
+ continue;
+
+ if (DT->isReachableFromEntry(Pred))
+ Blocks.push_back(Pred);
+ }
+}
+
/// HandleFree - Handle frees of entire structures whose dependency is a store
/// to a field of that structure.
bool DSE::HandleFree(CallInst *F) {
bool MadeChange = false;
- MemDepResult Dep = MD->getDependency(F);
+ AliasAnalysis::Location Loc = AliasAnalysis::Location(F->getOperand(0));
+ SmallVector<BasicBlock *, 16> Blocks;
+ Blocks.push_back(F->getParent());
+
+ while (!Blocks.empty()) {
+ BasicBlock *BB = Blocks.pop_back_val();
+ Instruction *InstPt = BB->getTerminator();
+ if (BB == F->getParent()) InstPt = F;
+
+ MemDepResult Dep = MD->getPointerDependencyFrom(Loc, false, InstPt, BB);
+ while (Dep.isDef() || Dep.isClobber()) {
+ Instruction *Dependency = Dep.getInst();
+ if (!hasMemoryWrite(Dependency) || !isRemovable(Dependency))
+ break;
+
+ Value *DepPointer =
+ GetUnderlyingObject(getStoredPointerOperand(Dependency));
- while (Dep.isDef() || Dep.isClobber()) {
- Instruction *Dependency = Dep.getInst();
- if (!hasMemoryWrite(Dependency) || !isRemovable(Dependency))
- return MadeChange;
-
- Value *DepPointer =
- GetUnderlyingObject(getStoredPointerOperand(Dependency));
-
- // Check for aliasing.
- if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
- return MadeChange;
-
- // DCE instructions only used to calculate that store
- DeleteDeadInstruction(Dependency, *MD);
- ++NumFastStores;
- MadeChange = true;
-
- // Inst's old Dependency is now deleted. Compute the next dependency,
- // which may also be dead, as in
- // s[0] = 0;
- // s[1] = 0; // This has just been deleted.
- // free(s);
- Dep = MD->getDependency(F);
- };
+ // Check for aliasing.
+ if (!AA->isMustAlias(F->getArgOperand(0), DepPointer))
+ break;
+
+ Instruction *Next = llvm::next(BasicBlock::iterator(Dependency));
+
+ // DCE instructions only used to calculate that store
+ DeleteDeadInstruction(Dependency, *MD);
+ ++NumFastStores;
+ MadeChange = true;
+
+ // Inst's old Dependency is now deleted. Compute the next dependency,
+ // which may also be dead, as in
+ // s[0] = 0;
+ // s[1] = 0; // This has just been deleted.
+ // free(s);
+ Dep = MD->getPointerDependencyFrom(Loc, false, Next, BB);
+ }
+
+ if (Dep.isNonLocal())
+ FindUnconditionalPreds(Blocks, BB, DT);
+ }
return MadeChange;
}
Modified: llvm/trunk/test/Transforms/DeadStoreElimination/free.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/DeadStoreElimination/free.ll?rev=143808&r1=143807&r2=143808&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/DeadStoreElimination/free.ll (original)
+++ llvm/trunk/test/Transforms/DeadStoreElimination/free.ll Sat Nov 5 05:48:42 2011
@@ -2,6 +2,9 @@
target datalayout = "e-p:64:64:64"
+declare void @free(i8* nocapture)
+declare noalias i8* @malloc(i64)
+
; CHECK: @test
; CHECK-NEXT: bitcast
; CHECK-NEXT: @free
@@ -26,10 +29,10 @@
ret void
}
-; CHECK: @test4
+; CHECK: @test3
; CHECK-NOT: store
; CHECK: ret void
-define void @test4() {
+define void @test3() {
%m = call i8* @malloc(i64 24)
store i8 0, i8* %m
%m1 = getelementptr i8* %m, i64 1
@@ -38,5 +41,20 @@
ret void
}
-declare void @free(i8*)
-declare i8* @malloc(i64)
+; PR11240
+; CHECK: @test4
+; CHECK-NOT: store
+; CHECK: ret void
+define void @test4(i1 %x) nounwind {
+entry:
+ %alloc1 = tail call noalias i8* @malloc(i64 4) nounwind
+ br i1 %x, label %skipinit1, label %init1
+
+init1:
+ store i8 1, i8* %alloc1
+ br label %skipinit1
+
+skipinit1:
+ tail call void @free(i8* %alloc1) nounwind
+ ret void
+}
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