[PATCH] D106776: [GlobalISel] Add a constant folding combine.

Thu Jul 29 05:19:45 PDT 2021

foad added a comment.

In D106776#2910090 <https://reviews.llvm.org/D106776#2910090>, @foad wrote:

>> These don't always get folded because when the instructions are created the constants are obscured by artifacts, or other reasons.
>
> For the AMDGPU fshl/fshr tests, the reason is that the foldable instructions are created during legalization, and the AMDGPU legalizer doesn't use CSEMIRBuilder yet.

Scratch that. The reason is that the constants are obscured by artifacts like G_ZEXT, which we don't constant fold (I previously tried that in D89392 <https://reviews.llvm.org/D89392>).

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https://reviews.llvm.org/D106776