[llvm-dev] llvm-mca for in-order CPUs (was Re: LLVM Weekly - #375, March 8th 2021)

[Andrew Savonichev via llvm-dev]

Hi Jay,

Jay Foad writes:
> On Mon, 8 Mar 2021 at 18:33, LLVM Weekly <list at llvmweekly.org> wrote:
>> * The llvm-mca static performance analysis tool now support in-order CPUs such
>>   as the Arm Cortex-A55. [d791695](https://reviews.llvm.org/rGd791695cb517).
>
> Thanks for doing this! I am very interested in using it for the AMDGPU
> target.

So far the feature was only tested for ARM in-order CPUs, so it will be
great if you can try it for the AMDGPU target!

> Have you given any thought to targets with MicroOpBufferSize=1?
> I understand that these are also "in order". I found that I could get
> some tests running with these changes:
> https://reviews.llvm.org/differential/diff/329308/
>
> But I am really shooting in the dark here. I don't have a good
> understanding of the difference between MicroOpBufferSize=0 and 1, and
> I am not even sure which setting is really best for AMDGPU.

Frankly, I don't know what is the difference between MicroOpBufferSize=0
and 1. We should probably treat them the same for MCA, so your changes
look good.

-- 
Andrew