[PATCH] D104953: [ObjC][ARC] Prevent moving objc_retain calls past objc_release calls that release the retained object

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

If we move a release past a retain, does this mean the retain/release pair is redundant? If that's the case, would it be easier to detect this case, during or after moving and then remove the redundant pair?



================
Comment at: llvm/test/Transforms/ObjCARC/code-motion.ll:43
+; Check that code motion is disabled.
+; Previously, ARC optimizer would move the release past the retain.
+
----------------
For this test, would be it be correct to move the `retain`/`release` calls to `%if.else`?

```
if.else:
  call void @alterRefCount()
  call i8* @llvm.objc.retain(i8* %[[OBJ]])
  call void @use(i8* %obj)
  call void @llvm.objc.release(i8* %[[OBJ]])
  br label %join
```


================
Comment at: llvm/test/Transforms/ObjCARC/code-motion.ll:51
+
+; CHECK: define void @test3(i8* %[[OBJ:.*]], i1
+; CHECK-NEXT: call i8* @llvm.objc.retain(i8* %[[OBJ]])
----------------
Given that the function is quite small and the key here is to check precisely *if/where* the calls are moved, it would probably be good to create check lines for the whole function?

You could also pre-commit the tests, so the impact of the change is more obvious in the diff itself.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D104953/new/

https://reviews.llvm.org/D104953