[PATCH] D75401: [ValueTracking] Let isGuaranteedNotToBeUndefOrPoison look into branch conditions of dominating blocks' terminators

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

You might need to check if the branch "must-be-executed" from the `CtxI`. See the example.



================
Comment at: llvm/lib/Analysis/ValueTracking.cpp:4563
 
+  if (CxtI) {
+    // If V is used as a branch condition before reaching CxtI, V cannot be
----------------
Style: early exit `!CtxI`.


================
Comment at: llvm/test/Transforms/InstSimplify/freeze.ll:58
+  ret i32 %fr
+}
----------------
@sanjoy Did have a point (I think). What happens if you have:

```
declare void @use(i1 %f) willreturn nounwind
declare void @exit()
define i1 @brcond_never_reached(i1 %c, i1 %c2) {
  %f = freeze i1 %c
  call void @use(i1 %f)
  call void exit();
  call void @use(i1 %f)
  br i1 %c, label %A, label %B
A:
  br i1 %c2, label %A2, label %B
A2:
  ret i1 %f
B:
  ret i1 %f
}



Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D75401/new/

https://reviews.llvm.org/D75401