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!unpredictable not propagated when combining select+add #63910

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chfast opened this issue Jul 17, 2023 · 1 comment
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!unpredictable not propagated when combining select+add #63910

chfast opened this issue Jul 17, 2023 · 1 comment
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llvm:instcombine missed-optimization

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chfast commented Jul 17, 2023 •
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When instcombine combines select+add into add+select the !unpredictable metadata is lost on the way.

define i64 @add_select(i1 %cond, i64 %x, i64 %y) {
  %add = add i64 %x, %y
  %ret = select i1 %cond, i64 %add, i64 %x, !unpredictable !0
  ret i64 %ret
}

!0 = !{}

→

define i64 @add_select(i1 %cond, i64 %x, i64 %y) {
  %add = select i1 %cond, i64 %y, i64 0
  %ret = add i64 %add, %x
  ret i64 %ret
}

https://godbolt.org/z/qq61noErs
@chfast chfast self-assigned this Jul 17, 2023
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chfast commented Jul 17, 2023

Proposed fix: https://reviews.llvm.org/D155461.

@chfast chfast closed this as completed in 9663180 Jul 19, 2023
@chfast chfast removed their assignment Jul 19, 2023
veselypeta pushed a commit to veselypeta/cherillvm that referenced this issue Sep 7, 2024
@chfast @veselypeta
[InstCombine] Preserve metadata when combining select+binop
21099a9 
Fixes llvm/llvm-project#63910

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D155461
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