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Fix objc_storeStrong pattern matching to catch a potential use of the

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old value after the store but before it is released.
This fixes rdar:/11116986.

llvm-svn: 156442
This commit is contained in:
Dan Gohman 2012-05-08 23:34:08 +00:00
parent c7857568af
commit b47d02f929
2 changed files with 105 additions and 9 deletions
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38
lib/Transforms/Scalar/ObjCARC.cpp
View File

@ -3925,18 +3925,38 @@ void ObjCARCContract::ContractRelease(Instruction *Release,
BasicBlock *BB = Release->getParent();
if (Load->getParent() != BB) return;
// Walk down to find the store.
// Walk down to find the store and the release, which may be in either order.
BasicBlock::iterator I = Load, End = BB->end();
++I;
AliasAnalysis::Location Loc = AA->getLocation(Load);
while (I != End &&
(&*I == Release ||
IsRetain(GetBasicInstructionClass(I)) ||
!(AA->getModRefInfo(I, Loc) & AliasAnalysis::Mod)))
++I;
StoreInst *Store = dyn_cast<StoreInst>(I);
if (!Store || !Store->isSimple()) return;
if (Store->getPointerOperand() != Loc.Ptr) return;
StoreInst *Store = 0;
bool SawRelease = false;
for (; !Store || !SawRelease; ++I) {
Instruction *Inst = I;
if (Inst == Release) {
SawRelease = true;
continue;
}
InstructionClass Class = GetBasicInstructionClass(Inst);
// Unrelated retains are harmless.
if (IsRetain(Class))
continue;
if (Store) {
// The store is the point where we're going to put the objc_storeStrong,
// so make sure there are no uses after it.
if (CanUse(Inst, Load, PA, Class))
return;
} else if (AA->getModRefInfo(Inst, Loc) & AliasAnalysis::Mod) {
// We are moving the load down to the store, so check for anything
// else which writes to the memory between the load and the store.
Store = dyn_cast<StoreInst>(Inst);
if (!Store || !Store->isSimple()) return;
if (Store->getPointerOperand() != Loc.Ptr) return;
}
}
Value *New = StripPointerCastsAndObjCCalls(Store->getValueOperand());

76
test/Transforms/ObjCARC/contract-storestrong.ll
View File

@ -4,6 +4,7 @@ target datalayout = "e-p:64:64:64"
declare i8* @objc_retain(i8*)
declare void @objc_release(i8*)
declare void @use_pointer(i8*)
@x = external global i8*
@ -57,3 +58,78 @@ entry:
tail call void @objc_release(i8* %tmp) nounwind
ret void
}
; Don't do this if there's a use of the old pointer vlaue between the store
; and the release.
; CHECK: define void @test3(i8* %newValue) {
; CHECK-NEXT: entry:
; CHECK-NEXT: %x0 = tail call i8* @objc_retain(i8* %newValue) nounwind
; CHECK-NEXT: %x1 = load i8** @x, align 8
; CHECK-NEXT: store i8* %x0, i8** @x, align 8
; CHECK-NEXT: tail call void @use_pointer(i8* %x1), !clang.arc.no_objc_arc_exceptions !0
; CHECK-NEXT: tail call void @objc_release(i8* %x1) nounwind, !clang.imprecise_release !0
; CHECK-NEXT: ret void
; CHECK-NEXT: }
define void @test3(i8* %newValue) {
entry:
%x0 = tail call i8* @objc_retain(i8* %newValue) nounwind
%x1 = load i8** @x, align 8
store i8* %newValue, i8** @x, align 8
tail call void @use_pointer(i8* %x1), !clang.arc.no_objc_arc_exceptions !0
tail call void @objc_release(i8* %x1) nounwind, !clang.imprecise_release !0
ret void
}
; Like test3, but with an icmp use instead of a call, for good measure.
; CHECK: define i1 @test4(i8* %newValue, i8* %foo) {
; CHECK-NEXT: entry:
; CHECK-NEXT: %x0 = tail call i8* @objc_retain(i8* %newValue) nounwind
; CHECK-NEXT: %x1 = load i8** @x, align 8
; CHECK-NEXT: store i8* %x0, i8** @x, align 8
; CHECK-NEXT: %t = icmp eq i8* %x1, %foo
; CHECK-NEXT: tail call void @objc_release(i8* %x1) nounwind, !clang.imprecise_release !0
; CHECK-NEXT: ret i1 %t
; CHECK-NEXT: }
define i1 @test4(i8* %newValue, i8* %foo) {
entry:
%x0 = tail call i8* @objc_retain(i8* %newValue) nounwind
%x1 = load i8** @x, align 8
store i8* %newValue, i8** @x, align 8
%t = icmp eq i8* %x1, %foo
tail call void @objc_release(i8* %x1) nounwind, !clang.imprecise_release !0
ret i1 %t
}
; Do form an objc_storeStrong here, because the use is before the store.
; CHECK: define i1 @test5(i8* %newValue, i8* %foo) {
; CHECK: %t = icmp eq i8* %x1, %foo
; CHECK: tail call void @objc_storeStrong(i8** @x, i8* %newValue) nounwind
define i1 @test5(i8* %newValue, i8* %foo) {
entry:
%x0 = tail call i8* @objc_retain(i8* %newValue) nounwind
%x1 = load i8** @x, align 8
%t = icmp eq i8* %x1, %foo
store i8* %newValue, i8** @x, align 8
tail call void @objc_release(i8* %x1) nounwind, !clang.imprecise_release !0
ret i1 %t
}
; Like test5, but the release is before the store.
; CHECK: define i1 @test6(i8* %newValue, i8* %foo) {
; CHECK: %t = icmp eq i8* %x1, %foo
; CHECK: tail call void @objc_storeStrong(i8** @x, i8* %newValue) nounwind
define i1 @test6(i8* %newValue, i8* %foo) {
entry:
%x0 = tail call i8* @objc_retain(i8* %newValue) nounwind
%x1 = load i8** @x, align 8
tail call void @objc_release(i8* %x1) nounwind, !clang.imprecise_release !0
%t = icmp eq i8* %x1, %foo
store i8* %newValue, i8** @x, align 8
ret i1 %t
}
!0 = metadata !{}