[PATCH] D75396: [ValueTracking] A value is never undef or poison if it must raise UB

[Juneyoung Lee via Phabricator via llvm-commits]

aqjune created this revision.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

This patch helps isGuaranteedNotToBeUndefOrPoison return true if the value
makes the program always undefined.

According to value tracking functions' comments, it is not still in consensus
whether a poison value can be bitwise or not, so conservatively only the case with
i1 is considered.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D75396

Files:
  llvm/lib/Analysis/ValueTracking.cpp


Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -4551,6 +4551,13 @@
       return true;
   }
 
+  if (auto I = dyn_cast<Instruction>(V)) {
+    if (programUndefinedIfFullPoison(I) && I->getType()->isIntegerTy(1))
+      // Note: once we have an agreement that poison is a value-wise concept,
+      // we can remove the isIntegerTy(1) constraint.
+      return true;
+  }
+
   return false;
 }
 


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