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

[Simon Wallis via llvm-commits]

simonwallis2 wrote:

> This sounds sensible. What was the difference between 3 and 4 for neoverse-n1? A value of 4 would help match the SWOG (and #136374), and if there isn't much in it would make a better value I believe.

For neoverse-n1, with a value of 4 I saw some small amount of noise but no overall improvement over the original value of 8.

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