[llvm] [AArch64] Update IssueWidth for Neoverse V1, N1, N3 (PR #154495)

[Simon Wallis via llvm-commits]

simonwallis2 wrote:

@vvereschaka Thanks for highlighting this.

All 3 of the failures reported by buildbot 193 in builds 10666 onwards are similar:
  #CHECK-NEXT: 1 1 0.12 U 1 MRS mrs x3, ID_AA64ZRF)_EL1
  Note: possible intended match here
  #CHECK-NEXT: 1 1 0.13 U 1 MRS mrs x3, ID_AA64ZRF)_EL1

For builds 10665 and earlier, the IssueWidth for V1 was 15, so the reciprocal throughput 1/15 was 0.07 to 2 decimal places.
>From build 10666, after PR154495 changed the IssueWidth to 8, the reciprocal throughput is 1/8 or 0.125.

The test case looks for 0.12. It has rounded 0.125 down. This is what I see on various linux hosts I tried.
The lllcm-clang-win-x-aarch64 build bot sees 0.13. It has rounded 0.125 up.

So we have inconsistent llvm-mca behaviour between this buildbot and other machines. I did not expect that.

As a short term hack to get this buildbot green again, it would be possible to modify these 3 test cases to expect rounding up when the host OS is windows, if that is the root of the differences.
But it would be better to make llvm-mca behave consistently.


https://github.com/llvm/llvm-project/pull/154495