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[ObjC][ARC] Ignore lifetime markers between *ReturnValue calls

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When eliminating a pair of

`llvm.objc.autoreleaseReturnValue`

followed by

`llvm.objc.retainAutoreleasedReturnValue`

we need to make sure that the instructions in between are safe to
ignore.

Other than bitcasts and useless GEPs, it's also safe to ignore lifetime
markers for both static allocas (lifetime.start/lifetime.end) and dynamic
allocas (stacksave/stackrestore).

These get added by the inliner as part of the return sequence and can
prevent the transformation from happening in practice.

Differential Revision: https://reviews.llvm.org/D69833
This commit is contained in:
Francis Visoiu Mistrih 2019-11-04 16:28:23 -08:00
parent 68f39de042
commit 47d1029788
2 changed files with 28 additions and 5 deletions
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29
llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
View File

@ -588,6 +588,33 @@ void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
static bool isSafeBetweenRVCalls(const Instruction *I) {
if (IsNoopInstruction(I))
return true;
auto *CB = dyn_cast<CallBase>(I);
if (!CB)
return false;
Intrinsic::ID IID = CB->getIntrinsicID();
if (IID == Intrinsic::not_intrinsic)
return false;
switch (IID) {
case Intrinsic::lifetime_start:
case Intrinsic::lifetime_end:
// The inliner adds new lifetime markers as part of the return sequence,
// which should be skipped when looking for paired return RV call.
LLVM_FALLTHROUGH;
case Intrinsic::stacksave:
case Intrinsic::stackrestore:
// If the inlined code contains dynamic allocas, the above applies as well.
return true;
default:
return false;
}
}
/// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
/// not a return value. Or, if it can be paired with an
/// objc_autoreleaseReturnValue, delete the pair and return true.
@ -634,7 +661,7 @@ ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
if (I != Begin) {
do
--I;
while (I != Begin && IsNoopInstruction(&*I));
while (I != Begin && isSafeBetweenRVCalls(&*I));
if (GetBasicARCInstKind(&*I) == ARCInstKind::AutoreleaseRV &&
EquivalentArgs.count(GetArgRCIdentityRoot(&*I))) {
Changed = true;

4
llvm/test/Transforms/ObjCARC/post-inlining.ll
View File

@ -76,9 +76,7 @@ declare void @llvm.lifetime.end.p0i8(i64, i8*)
; CHECK: entry:
; CHECK-NEXT: %obj = alloca i8
; CHECK-NEXT: call void @llvm.lifetime.start.p0i8(i64 8, i8* %obj)
; CHECK-NEXT: %0 = tail call i8* @llvm.objc.autoreleaseReturnValue(i8* %call.i)
; CHECK-NEXT: call void @llvm.lifetime.end.p0i8(i64 8, i8* %obj)
; CHECK-NEXT: %1 = tail call i8* @llvm.objc.retain(i8* %call.i)
; CHECK-NEXT: ret i8* %call.i
; CHECK-NEXT: }
define i8* @testLifetime(i8* %call.i) {
@ -100,9 +98,7 @@ declare void @llvm.stackrestore(i8*)
; CHECK: entry:
; CHECK-NEXT: %save = tail call i8* @llvm.stacksave()
; CHECK-NEXT: %obj = alloca i8, i8 %arg
; CHECK-NEXT: %0 = tail call i8* @llvm.objc.autoreleaseReturnValue(i8* %call.i)
; CHECK-NEXT: call void @llvm.stackrestore(i8* %save)
; CHECK-NEXT: %1 = tail call i8* @llvm.objc.retain(i8* %call.i)
; CHECK-NEXT: ret i8* %call.i
; CHECK-NEXT: }
define i8* @testStack(i8* %call.i, i8 %arg) {