[PATCH] D61228: [PowerPC] Set the innermost hot loop(from PGO) to align 32 bytes

[Hal Finkel via Phabricator via llvm-commits]

hfinkel added a comment.

In D61228#1505513 <https://reviews.llvm.org/D61228#1505513>, @nemanjai wrote:

> > Can you explain why we don't always do this? You're checking for profiling data but then not using it?
>
> I think the idea is that with PGO data, we are more certain that the hotness information is actually meaningful - since the alignment directive will only be emitted for loops that are "hot". Without PGO data, we will align a majority of loops which may be overkill. But this should be clearly stated in the comment though.


Okay, but we just call MBB->getParent()->getFunction().hasProfileData(), where do we actually check that the loop is hot?

Also, even if we align the majority of loops, how much does that really cost us? The code-size impact could be minor compared to the perf improvement, and if so, we should just always do it. It is still true that most users don't use PGO.


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