[PATCH] D141980: [X86] Transform slow LEA_B_I_D/LEA_SLOWBASE_I -> LEA_IS_D/LEA_IS iff base == index

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n added a comment.

In D141980#4061628 <https://reviews.llvm.org/D141980#4061628>, @RKSimon wrote:

> An LEA with scale > 1 also forces a slower computation on the AGUs for most AMD cpus

I see, is there a flag you know of that you think should guard the transform?

Although keep in mind, this is only hooked in for targets that have `TuningSlow3OpsLEA` which AFAICT only covers:

  KNL
  ICL
  ICX
  TGL
  CNL
  SKX
  CLX
  CPX
  SKL
  ADL
  HSW
  BDW
  SNB
  IVB

Which are just the intel lineup. The only concerning one is `ADL` b.c. it has some `atom` cores and there where concerns `atom` has slow LEA_IS although looking at `ADL-E` on `uops.info` seems `LEA_IS_D` is same as `LEA_B_I_D` (2c latency each) so probably still fine to keep this transform (truthfully `ADL` probably shouldn't have `TuningSlow3OpsLEA` set as 2uops basically == 1x lea in worst case LEA on the E cores and the P cores have fast LEA).


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https://reviews.llvm.org/D141980