[llvm] [AggressiveInstCombine] POPCNT generation for bit-count pattern (PR #177109)

[Craig Topper via llvm-commits]

topperc wrote:

> > I reran the opt-benchmark on both of the PRs and neither are showing the changes that were originally reported.
> > Looking back at your original commit, it matched ` x = (x & 0x07070707) + ((x >> 4) & 0x07070707);` instead of `x = (x & 0x0F0F0F0F) + ((x >> 4) & 0x0F0F0F0F);` I'm guessing InstCombine changed 0x0F0F0F0F to 0x07070707 before this pass runs.
> 
> Yes, you are right. InstCombine is changing the constant. What should we do then? Update the PR or create a new PR to handle this case.

I think we need to update the PR. Committing code that will never match isn't useful.

https://github.com/llvm/llvm-project/pull/177109