[llvm] [InstCombine] Support well-defined recurrences in isGuaranteedNotToBeUndefOrPoison (PR #150420)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Cullen Rhodes (c-rhodes)

<details>
<summary>Changes</summary>

This function currently doesn't detect well-defined recurrences that can't produce undef or poison. This prevents instcombine from pushing freezes through GEPs to the ptr which may be undef or poison, when the offset is a well-defined recurrence, as the tests added in #<!-- -->145541 demonstrate.

This patch fixes this by pulling existing code from foldFreezeIntoRecurrence in instcombine, which can detect whether a PHI produces undef/poison, so it can be reused by
isGuaranteedNotToBeUndefOrPoison in ValueTracking.

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Full diff: https://github.com/llvm/llvm-project/pull/150420.diff


9 Files Affected:

- (modified) llvm/include/llvm/Analysis/ValueTracking.h (+8) 
- (modified) llvm/lib/Analysis/ValueTracking.cpp (+67) 
- (modified) llvm/lib/Transforms/InstCombine/InstructionCombining.cpp (+9-53) 
- (modified) llvm/test/Transforms/Attributor/dereferenceable-1.ll (+2-2) 
- (modified) llvm/test/Transforms/Attributor/value-simplify.ll (+6-2) 
- (modified) llvm/test/Transforms/InstCombine/freeze-landingpad.ll (+4-5) 
- (modified) llvm/test/Transforms/InstCombine/freeze.ll (+11-11) 
- (modified) llvm/test/Transforms/LoopUnroll/runtime-exit-phi-scev-invalidation.ll (+3-5) 
- (modified) llvm/test/Transforms/SimpleLoopUnswitch/nontrivial-unswitch-select.ll (+1-2) 


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https://github.com/llvm/llvm-project/pull/150420