[PATCH] D91716: AMDGPU/GlobalISel: Calculate isKnownNeverNaN for fminnum and fmaxnum

[Matt Arsenault via Phabricator via llvm-commits]

arsenm added inline comments.


================
Comment at: llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-fminnum.mir:773
     %3:_(s32) = COPY $vgpr2
     %4:_(s32) = G_FMINNUM %2, %3
     $vgpr0 = COPY %4
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Petar.Avramovic wrote:
> 
> 
> 
> ```
> return isKnownNeverNaN(Op.getOperand(0), SNaN, Depth + 1) ||
>        isKnownNeverNaN(Op.getOperand(1), SNaN, Depth + 1);
> }
> ```
> This is legalized first. `%2` is isKnownNeverSNaN with IEEE = true, but since inputs for `%2:_(s32) = G_FMAXNUM %0, %1` are not yet canonicalized isKnownNeverSNaN will fail and canonicalize is inserted. However since we know what will happen with `'%2:_(s32) = G_FMAXNUM %0, %1` we declare it  isKnownNeverSNaN to not depend on order of legalization.
> 
> 
The legalization order doesn't matter. These operations have their own independent semantics. isKnownNeverNaN needs to understand both pairs


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  https://reviews.llvm.org/D91716/new/

https://reviews.llvm.org/D91716