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Incorrect transform in loop not detected #951

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nikic opened this issue Oct 30, 2023 · 0 comments
Closed

Incorrect transform in loop not detected #951

nikic opened this issue Oct 30, 2023 · 0 comments

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@nikic
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nikic commented Oct 30, 2023

I believe this transform is not correct, but it is not detected even if src-unroll/tgt-unroll are used: https://alive2.llvm.org/ce/z/7nh8kF

I am able to trigger a failure if I replace %v with a specific constant: https://alive2.llvm.org/ce/z/mxPXKl

Am I missing something here?
nikic referenced this issue in llvm/llvm-project Oct 30, 2023
@XChy
[InstCombine] Fold Ext(i1) Pred shr(A, BW - 1) => i1 Pred A s< 0 (#68244
b22917e 
)

Resolves #67916 .
This patch folds `Ext(icmp (A, xxx)) Pred shr(A, BW - 1)` into `i1 Pred
A s< 0`.
[Alive2](https://alive2.llvm.org/ce/z/k53Xwa).
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