[ObjCARC] Do not turn a call to @objc_autoreleaseReturnValue into a call

to @objc_autorelease if its operand is a PHI and the PHI has an
equivalent value that is used by a return instruction.

For example, ARC optimizer shouldn't replace the call in the following
example, as doing so breaks the AutoreleaseRV/RetainRV optimization:

  %v1 = bitcast i32* %v0 to i8*
  br label %bb3
bb2:
  %v3 = bitcast i32* %v2 to i8*
  br label %bb3
bb3:
  %p = phi i8* [ %v1, %bb1 ], [ %v3, %bb2 ]
  %retval = phi i32* [ %v0, %bb1 ], [ %v2, %bb2 ] ; equivalent to %p
  %v4 = tail call i8* @objc_autoreleaseReturnValue(i8* %p)
  ret i32* %retval

Also, make sure ObjCARCContract replaces @objc_autoreleaseReturnValue's
operand uses with its value so that the call gets tail-called.

rdar://problem/15894705

llvm-svn: 323009

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index 99ed6863c22..ecec85444b1 100644
--- a/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/llvm/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -652,6 +652,11 @@ void ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F,
 
   SmallVector<const Value *, 2> Users;
   Users.push_back(Ptr);
+
+  // Add PHIs that are equivalent to Ptr to Users.
+  if (const PHINode *PN = dyn_cast<PHINode>(Ptr))
+    getEquivalentPHIs(*PN, Users);
+
   do {
     Ptr = Users.pop_back_val();
     for (const User *U : Ptr->users()) {