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Be more aggressive with ObjCARCContract.cpp #130630

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Be more aggressive with ObjCARCContract.cpp #130630

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22 changes: 15 additions & 7 deletions llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -243,13 +243,21 @@ static StoreInst *findSafeStoreForStoreStrongContraction(LoadInst *Load,

// Ok, now we know we have not seen a store yet.

// If Inst is a retain, we don't care about it as it doesn't prevent moving
// the load to the store.
//
// TODO: This is one area where the optimization could be made more
// aggressive.
if (IsRetain(Class))
continue;
// If Inst is a retain, we can be more aggressive by checking if:
// 1. The retain is on an unrelated object (different RC identity root)
// 2. The retain's argument doesn't alias with our load location
// In these cases, we can safely move past the retain.
if (IsRetain(Class)) {
Value *RetainArg = GetArgRCIdentityRoot(Inst);
Value *LoadRoot = GetRCIdentityRoot(Load);
if (RetainArg != LoadRoot && !AA->alias(MemoryLocation::get(Load),
MemoryLocation::getBeforeOrAfter(RetainArg))) {
continue;
}
// If the retain is on the same object or we can't prove no aliasing,
// be conservative and bail out
return nullptr;
}

// See if Inst can write to our load location, if it can not, just ignore
// the instruction.
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33 changes: 32 additions & 1 deletion llvm/test/Transforms/ObjCARC/contract.ll
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Expand Up @@ -32,7 +32,7 @@ entry:
ret void
}

; Merge objc_retain and objc_autorelease into objc_retainAutorelease.
; Merge objc_retain and objc_autorelease into objc_retainAutoreleasedReturnValue.

; CHECK-LABEL: define void @test2(
; CHECK: tail call ptr @llvm.objc.retainAutorelease(ptr %x) [[NUW:#[0-9]+]]
Expand Down Expand Up @@ -238,3 +238,34 @@ declare void @llvm.objc.clang.arc.use(...) nounwind
declare void @llvm.objc.clang.arc.noop.use(...) nounwind

; CHECK: attributes [[NUW]] = { nounwind }

; CHECK-LABEL: define void @test_aggressive_retain_opt(
; CHECK: tail call ptr @llvm.objc.retainAutoreleasedReturnValue(ptr %p)
; CHECK: }
define void @test_aggressive_retain_opt() {
%p = call ptr @returner()
%unrelated = call ptr @returner()
tail call ptr @llvm.objc.retain(ptr %unrelated) nounwind
tail call ptr @llvm.objc.retain(ptr %p) nounwind
ret void
}

; CHECK-LABEL: define void @test_aggressive_retain_opt_alias(
; CHECK: tail call ptr @llvm.objc.retain(ptr %p)
; CHECK: }
define void @test_aggressive_retain_opt_alias(ptr %p, ptr %q) {
store ptr %p, ptr %q
tail call ptr @llvm.objc.retain(ptr %p) nounwind
ret void
}

; CHECK-LABEL: define void @test_aggressive_retain_opt_no_alias(
; CHECK: tail call ptr @llvm.objc.retainAutoreleasedReturnValue(ptr %p)
; CHECK: }
define void @test_aggressive_retain_opt_no_alias() {
%p = call ptr @returner()
%q = alloca ptr
store ptr null, ptr %q
tail call ptr @llvm.objc.retain(ptr %p) nounwind
ret void
}
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