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

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

In D141980#4062735 <https://reviews.llvm.org/D141980#4062735>, @goldstein.w.n wrote:

> 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).

I find it odd that KNL is in that list. KNL is based on Silvermont so I'd expect it to have `TuningSlowLEA` instead.


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