Merge pull request #3161 from apple/PR-81668577

[ObjC][ARC] Don't form a StoreStrong call if it is unsafe to move the release call

Author: ahatanaka

llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp

@@ -226,13 +226,6 @@ static StoreInst *findSafeStoreForStoreStrongContraction(LoadInst *Load,
     // of Inst.
     ARCInstKind Class = GetBasicARCInstKind(Inst);
 
-    // If Inst is an unrelated retain, we don't care about it.
-    //
-    // TODO: This is one area where the optimization could be made more
-    // aggressive.
-    if (IsRetain(Class))
-      continue;
-
     // If we have seen the store, but not the release...
     if (Store) {
       // We need to make sure that it is safe to move the release from its
@@ -248,8 +241,18 @@ static StoreInst *findSafeStoreForStoreStrongContraction(LoadInst *Load,
       return nullptr;
     }
 
-    // Ok, now we know we have not seen a store yet. See if Inst can write to
-    // our load location, if it can not, just ignore the instruction.
+    // Ok, now we know we have not seen a store yet.
+
+    // If Inst is a retain, we don't care about it as it doesn't prevent moving
+    // the load to the store.
+    //
+    // TODO: This is one area where the optimization could be made more
+    // aggressive.
+    if (IsRetain(Class))
+      continue;
+
+    // See if Inst can write to our load location, if it can not, just ignore
+    // the instruction.
     if (!isModSet(AA->getModRefInfo(Inst, Loc)))
       continue;
 

llvm/test/Transforms/ObjCARC/contract-storestrong.ll

@@ -256,6 +256,25 @@ define i8* @test13(i8* %a0, i8* %a1, i8** %addr, i8* %new) {
   ret i8* %retained
 }
 
+; Cannot form a storeStrong call because it's unsafe to move the release call to
+; the store.
+
+; CHECK-LABEL: define void @test14(
+; CHECK: %[[V0:.*]] = load i8*, i8** %a
+; CHECK: %[[V1:.*]] = call i8* @llvm.objc.retain(i8* %p)
+; CHECK: store i8* %[[V1]], i8** %a
+; CHECK: %[[V2:.*]] = call i8* @llvm.objc.retain(i8* %[[V0]])
+; CHECK: call void @llvm.objc.release(i8* %[[V2]])
+
+define void @test14(i8** %a, i8* %p) {
+  %v0 = load i8*, i8** %a, align 8
+  %v1 = call i8* @llvm.objc.retain(i8* %p)
+  store i8* %p, i8** %a, align 8
+  %v2  = call i8* @llvm.objc.retain(i8* %v0)
+  call void @llvm.objc.release(i8* %v0)
+  ret void
+}
+
 !0 = !{}
 
 ; CHECK: attributes [[NUW]] = { nounwind }