[PATCH] D132837: [ISel] Enable generating more fma instructions.

[Jay Foad via Phabricator via llvm-commits]

foad added a subscriber: deadalnix.
foad added a comment.

In D132837#3802978 <https://reviews.llvm.org/D132837#3802978>, @foad wrote:

> In D132837#3802595 <https://reviews.llvm.org/D132837#3802595>, @foad wrote:
>
>> I am a little confused by the test changes: one of them now uses fmac instead of mac, and the other uses mad instead of fma.
>
> This is not your fault and need not block the patch. The choice of fma vs fmad depends on whether the combiner is running pre- or post-legalization, and it is a bit random because the pre-legalization combiner does not always re-run combines on new nodes that it creates, so some stuff is (wrongly) left for the post-legalizer combiner to clean up.

@deadalnix @RKSimon I debugged this to a case where running the pre-legalization combiner twice in a row would do extra combines that a single pass missed, and D127115 <https://reviews.llvm.org/D127115> did not help. Is this to be expected? Is it worth debugging more to work out exactly why some combines were missed the first time?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D132837/new/

https://reviews.llvm.org/D132837