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

[Philip Reames via Phabricator via llvm-commits]

reames requested changes to this revision.
reames added inline comments.
This revision now requires changes to proceed.


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


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Comment at: llvm/lib/Analysis/ValueTracking.cpp:4579
+    if (!DT)
+      return hasCond(CxtI->getParent(), V);
+    else {
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This is incorrect.  Consider:
b = freeze a
throw_if_a_would_be_poison()
if (a == 5) {}

You can only use branches which either a) dominate the freeze's uses, or b) are guaranteed to execute if any of those uses execute.   (a) is a subcase of (b) which happens to be cheap to check.  Note that phrasing in terms of "uses" here, not the freeze def. 


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  https://reviews.llvm.org/D75401/new/

https://reviews.llvm.org/D75401