Remove an optimization where we were changing an objc_autorelease into an objc_autoreleaseReturnValue.
The semantics of ARC implies that a pointer passed into an objc_autorelease
must live until some point (potentially down the stack) where an
autorelease pool is popped. On the other hand, an
objc_autoreleaseReturnValue just signifies that the object must live
until the end of the given function at least.
Thus objc_autorelease is stronger than objc_autoreleaseReturnValue in
terms of the semantics of ARC* implying that performing the given
strength reduction without any knowledge of how this relates to
the autorelease pool pop that is further up the stack violates the
semantics of ARC.
*Even though objc_autoreleaseReturnValue if you know that no RV
optimization will occur is more computationally expensive.
llvm-svn: 178612
diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index a956cae..5ac8c8e 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -1440,8 +1440,7 @@
break;
}
- // objc_autorelease(x), objc_autoreleaseRV -> objc_release(x) if x is
- // otherwise unused.
+ // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
if (IsAutorelease(Class) && Inst->use_empty()) {
CallInst *Call = cast<CallInst>(Inst);
const Value *Arg = Call->getArgOperand(0);
@@ -2861,20 +2860,6 @@
DependingInstructions.clear();
Visited.clear();
- // Convert the autorelease to an autoreleaseRV, since it's
- // returning the value.
- if (AutoreleaseClass == IC_Autorelease) {
- DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Converting autorelease "
- "=> autoreleaseRV since it's returning a value.\n"
- " In: " << *Autorelease
- << "\n");
- Autorelease->setCalledFunction(getAutoreleaseRVCallee(F.getParent()));
- DEBUG(dbgs() << " Out: " << *Autorelease
- << "\n");
- Autorelease->setTailCall(); // Always tail call autoreleaseRV.
- AutoreleaseClass = IC_AutoreleaseRV;
- }
-
// Check that there is nothing that can affect the reference
// count between the retain and the call.
// Note that Retain need not be in BB.