[PATCH] D116952: [ConstantFolding] Respect denormal handling mode attributes when folding instructions

[Nuno Lopes via Phabricator via llvm-commits]

nlopes added a comment.

In D116952#3600716 <https://reviews.llvm.org/D116952#3600716>, @shchenz wrote:

>   define zeroext i1 @foo() #0 {
>     %_add = fadd fast double 1.264810e-321, 3.789480e-321
>     %_res = fcmp fast une double %_add, 5.054290e-321
>     ret i1 %_res
>   }
>   
>   attributes #0 = { "denormal-fp-math"="positive-zero" }
>
>   llc 1.ll -mtriple=powerpc64le-unknown-linux-gnu
>
> Hi, this patch causes mis-compile for above case, now `%_res` is true while before this patch it is false. We can not handle the denormal constantFP in fcmp? Will the denormal constantFP be in other opcodes as well?

Alive says that LLVM is correct:

  define i1 @foo() denormal-fp-math=positive-zero,positive-zero {
    %_add = fadd double 0.000000, 0.000000, exceptions=ignore
    %_res = fcmp une double %_add, 0.000000
    ret i1 %_res
  }
  =>
  define i1 @foo() noread nowrite nofree willreturn denormal-fp-math=positive-zero,positive-zero {
    ret i1 1
  }
  Transformation seems to be correct!


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