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Enhance DSE to handle the case where a free call makes more than

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one store dead. This is especially noticeable in
SingleSource/Benchmarks/Shootout/objinst.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118875 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-11-12 02:19:17 +00:00
parent 02df7e90cf
commit 720a2ed6d9
2 changed files with 38 additions and 12 deletions
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36
lib/Transforms/Scalar/DeadStoreElimination.cpp
View File

@ -59,6 +59,7 @@ namespace {
bool runOnBasicBlock(BasicBlock &BB);
bool handleFreeWithNonTrivialDependency(const CallInst *F,
Instruction *Inst,
MemDepResult Dep);
bool handleEndBlock(BasicBlock &BB);
bool RemoveUndeadPointers(Value *Ptr, uint64_t killPointerSize,
@ -212,7 +213,7 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
// Handle frees whose dependencies are non-trivial.
if (const CallInst *F = isFreeCall(Inst)) {
MadeChange |= handleFreeWithNonTrivialDependency(F, InstDep);
MadeChange |= handleFreeWithNonTrivialDependency(F, Inst, InstDep);
continue;
}
@ -298,23 +299,34 @@ bool DSE::runOnBasicBlock(BasicBlock &BB) {
/// handleFreeWithNonTrivialDependency - Handle frees of entire structures whose
/// dependency is a store to a field of that structure.
bool DSE::handleFreeWithNonTrivialDependency(const CallInst *F,
Instruction *Inst,
MemDepResult Dep) {
AliasAnalysis &AA = getAnalysis<AliasAnalysis>();
MemoryDependenceAnalysis &MD = getAnalysis<MemoryDependenceAnalysis>();
Instruction *Dependency = Dep.getInst();
if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
return false;
do {
Instruction *Dependency = Dep.getInst();
if (!Dependency || !doesClobberMemory(Dependency) || !isElidable(Dependency))
return false;
Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
Value *DepPointer = getPointerOperand(Dependency)->getUnderlyingObject();
// Check for aliasing.
if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
AliasAnalysis::MustAlias)
return false;
// Check for aliasing.
if (AA.alias(F->getArgOperand(0), 1, DepPointer, 1) !=
AliasAnalysis::MustAlias)
return false;
// DCE instructions only used to calculate that store
DeleteDeadInstruction(Dependency);
++NumFastStores;
// DCE instructions only used to calculate that store
DeleteDeadInstruction(Dependency);
++NumFastStores;
// 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(Inst);
} while (!Dep.isNonLocal());
return true;
}

14
test/Transforms/DeadStoreElimination/free.ll
View File

@ -24,3 +24,17 @@ define void @test2({i32, i32}* %P) {
ret void
}
; CHECK: @test4
; CHECK-NOT: store
; CHECK: ret void
define void @test4() {
%m = call i8* @malloc(i64 24)
store i8 0, i8* %m
%m1 = getelementptr i8* %m, i64 1
store i8 1, i8* %m1
call void @free(i8* %m)
ret void
}
declare void @free(i8*)
declare i8* @malloc(i64)