[llvm] [EarlyIfConversion] Limit critical-path growth for strongly biased branches (PR #228709)

[Jonathan Cohen via llvm-commits]

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jcohen-apple wrote:

Ran and measured this on a larger set of benchmark suites. 

- if-converted branches decreased 3.3%
- Most of these are not in hot code
- Of those that were in hot code I observed 2 workloads that showed small improvement (~0.5% cycles decreased).

Overall - at least from a static compilation standpoint - this seems good to land as-is. Since I don't see any significant regressions we probably don't need the additional loop carried dependency check. I haven't checked how that affects PGO however.

I can only test an Apple platforms and give an LGTM from our end.

https://github.com/llvm/llvm-project/pull/228709