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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178612 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 1 insertions, 16 deletions

diff --git a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index a956caeffe..5ac8c8e6c2 100644
--- a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -1440,8 +1440,7 @@ void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
       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 @@ void ObjCARCOpt::OptimizeReturns(Function &F) {
         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.