[PATCH] D92739: [ValueTracking] Branch on poison is UB

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: aqjune, spatel, lebedev.ri, nlopes.
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Teach getGuaranteedNonPoisonOps() and thus programUndefinedIfPoison() that branching on poison is undefined behavior.

LangRef for `br` and `switch`:

> If ‘cond’ is poison or undef, this instruction has undefined behavior.
>  If ‘value’ is poison or undef, this instruction has undefined behavior.

Ran into this while attempting to fix https://bugs.llvm.org/show_bug.cgi?id=46943, where this would be helpful to detect whether there is an existing UB-on-poison use of the postinc IV, and branches are the most important use when it comes to loops.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D92739

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Analysis/ScalarEvolution/exact-exit-count-more-precise.ll
  llvm/test/Analysis/ScalarEvolution/limit-depth.ll
  llvm/test/Analysis/ScalarEvolution/max-backedge-taken-count-guard-info.ll
  llvm/test/Analysis/ScalarEvolution/trip-count12.ll
  llvm/test/Analysis/ScalarEvolution/trip-count9.ll
  llvm/test/Transforms/IndVarSimplify/X86/loop-invariant-conditions.ll
  llvm/test/Transforms/IndVarSimplify/lftr-reuse.ll
  llvm/test/Transforms/LoopUnroll/runtime-small-upperbound.ll
  llvm/test/Transforms/LoopVectorize/X86/small-size.ll
  llvm/test/Transforms/LoopVectorize/consecutive-ptr-uniforms.ll
  llvm/unittests/Analysis/ValueTrackingTest.cpp

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