[PATCH] D32605: Recognize CTLZ builtin

[Renato Golin via Phabricator via llvm-commits]

rengolin added a comment.

In https://reviews.llvm.org/D32605#750202, @joerg wrote:

> That's not true. ARMv4 for example has no clz, it's a V5T feature.


I keep forgetting about ARMv4... :)

My base point here is that we should avoid arguments like "the issue that should be resolved by CPU owner".

For example, no one I know *benchmarks on ARMv4*. I know people that test stuff on it (Joerg, Saleem), but not benchmark. This would have passed unnoticed for how long?

I think we need to take a more conservative view on optimisations, and get either an approval or "don't care" by CPU ownser, and *then* let them them work out the problems later, if they come.

I particularly care about ARMv7+, and that's why I wanted to make sure Joerg was happy, because he cares about areas I usually don't.

And I agree with Joerg, this will have a large impact on ARMv4, not just performance, but also code size. This feature *needs* a hook.

cheers,
--renato


Repository:
  rL LLVM

https://reviews.llvm.org/D32605