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Constant pointers to objects don't need reference counting. 

llvm-svn: 138242
This commit is contained in:
Dan Gohman 2011-08-22 17:29:11 +00:00
parent bce94fded8
commit 56e1cef705
2 changed files with 46 additions and 0 deletions
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13
llvm/lib/Transforms/Scalar/ObjCARC.cpp
View File

@ -515,6 +515,10 @@ static bool IsObjCIdentifiedObject(const Value *V) {
const Value *Pointer =
StripPointerCastsAndObjCCalls(LI->getPointerOperand());
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
// A constant pointer can't be pointing to an object on the heap. It may
// be reference-counted, but it won't be deleted.
if (GV->isConstant())
return true;
StringRef Name = GV->getName();
// These special variables are known to hold values which are not
// reference-counted pointers.
@ -2744,6 +2748,15 @@ ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
// regardless of what possible decrements or uses lie between them.
bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
// A constant pointer can't be pointing to an object on the heap. It may
// be reference-counted, but it won't be deleted.
if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
if (const GlobalVariable *GV =
dyn_cast<GlobalVariable>(
StripPointerCastsAndObjCCalls(LI->getPointerOperand())))
if (GV->isConstant())
KnownSafe = true;
// If a pair happens in a region where it is known that the reference count
// is already incremented, we can similarly ignore possible decrements.
bool KnownSafeTD = true, KnownSafeBU = true;

33
llvm/test/Transforms/ObjCARC/basic.ll
View File

@ -1638,6 +1638,39 @@ entry:
ret void
}
; Constant pointers to objects don't need reference counting.
@constptr = external constant i8*
@something = external global i8*
; CHECK: define void @test60(
; CHECK-NOT: @objc_
; CHECK: }
define void @test60() {
%t = load i8** @constptr
%s = load i8** @something
call i8* @objc_retain(i8* %s)
call void @callee()
call void @use_pointer(i8* %t)
call void @objc_release(i8* %s)
ret void
}
; Constant pointers to objects don't need to be considered related to other
; pointers.
; CHECK: define void @test61(
; CHECK-NOT: @objc_
; CHECK: }
define void @test61() {
%t = load i8** @constptr
call i8* @objc_retain(i8* %t)
call void @callee()
call void @use_pointer(i8* %t)
call void @objc_release(i8* %t)
ret void
}
declare void @bar(i32 ()*)
; A few real-world testcases.