[llvm] [PatternMatch] Use `m_SpecificCmp` matchers. NFC. (PR #100878)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> Okay, so it looks like the top 5 improvements/regressions are very noisy. I did wonder why I wasn't able to reproduce all regressions on previous PRs.
> 
> To mostly avoid this problem I collect per-benchmark stddev data and only consider differences starting at 3-4 sigma significant.

Oops, I forgot to disable ASLR after the last power outage in my lab :(
With ASLR off:
```
Top 5 improvements:
Top 5 regressions:
Overall: 0.00000013%
```

https://github.com/llvm/llvm-project/pull/100878