From 6c189ecbe6d11583dc54289a2e8d8f35add01c82 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Fri, 13 Apr 2012 01:08:28 +0000
Subject: [PATCH] Use the new Use-aware dominates method to apply the objc
 runtime library return value optimization for phi uses. Even when the phi
 itself is not dominated, the specific use may be dominated.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154647 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/ObjCARC.cpp   | 13 +++++--------
 test/Transforms/ObjCARC/contract.ll | 18 ++++++++++++++++++
 2 files changed, 23 insertions(+), 8 deletions(-)

diff --git a/lib/Transforms/Scalar/ObjCARC.cpp b/lib/Transforms/Scalar/ObjCARC.cpp
index 62c4694616f..40b0b206168 100644
--- a/lib/Transforms/Scalar/ObjCARC.cpp
+++ b/lib/Transforms/Scalar/ObjCARC.cpp
@@ -4109,16 +4109,12 @@ bool ObjCARCContract::runOnFunction(Function &F) {
         Use &U = UI.getUse();
         unsigned OperandNo = UI.getOperandNo();
         ++UI; // Increment UI now, because we may unlink its element.
-        Instruction *UserInst = dyn_cast<Instruction>(U.getUser());
-        if (!UserInst)
-          continue;
-        // FIXME: dominates should return true for unreachable UserInst.
-        if (DT->isReachableFromEntry(UserInst->getParent()) &&
-            DT->dominates(Inst, UserInst)) {
+        if (DT->isReachableFromEntry(U) &&
+            DT->dominates(Inst, U)) {
           Changed = true;
           Instruction *Replacement = Inst;
           Type *UseTy = U.get()->getType();
-          if (PHINode *PHI = dyn_cast<PHINode>(UserInst)) {
+          if (PHINode *PHI = dyn_cast<PHINode>(U.getUser())) {
             // For PHI nodes, insert the bitcast in the predecessor block.
             unsigned ValNo =
               PHINode::getIncomingValueNumForOperand(OperandNo);
@@ -4139,7 +4135,8 @@ bool ObjCARCContract::runOnFunction(Function &F) {
               }
           } else {
             if (Replacement->getType() != UseTy)
-              Replacement = new BitCastInst(Replacement, UseTy, "", UserInst);
+              Replacement = new BitCastInst(Replacement, UseTy, "",
+                                            cast<Instruction>(U.getUser()));
             U.set(Replacement);
           }
         }
diff --git a/test/Transforms/ObjCARC/contract.ll b/test/Transforms/ObjCARC/contract.ll
index 04ae3ca505f..c48f8a534fa 100644
--- a/test/Transforms/ObjCARC/contract.ll
+++ b/test/Transforms/ObjCARC/contract.ll
@@ -143,3 +143,21 @@ define i8* @test7(i8* %p) {
   %2 = tail call i8* @objc_autoreleaseReturnValue(i8* %p)
   ret i8* %p
 }
+
+; Do the return value substitution for PHI nodes too.
+
+; CHECK: define i8* @test8(
+; CHECK: %retval = phi i8* [ %p, %if.then ], [ null, %entry ]
+; CHECK: }
+define i8* @test8(i1 %x, i8* %c) {
+entry:
+  br i1 %x, label %return, label %if.then
+
+if.then:                                          ; preds = %entry
+  %p = call i8* @objc_retain(i8* %c) nounwind
+  br label %return
+
+return:                                           ; preds = %if.then, %entry
+  %retval = phi i8* [ %c, %if.then ], [ null, %entry ]
+  ret i8* %retval
+}
-- 
2.34.1