[PATCH] D59688: [X86] Make post-ra scheduling macrofusion-aware.

[Andrea Di Biagio via Phabricator via llvm-commits]

andreadb added a subscriber: lebedev.ri.
andreadb added a comment.

In D59688#1439408 <https://reviews.llvm.org/D59688#1439408>, @courbet wrote:

> > I plan to run some experiments today using your patch.
>
> That's great, thanks.


Sorry, I was over optimistic about my other workload. I don't think I'll get a chance to get any perf numbers anytime soon.

That being said, I tried your patch on a few small examples on some different targets, and results seem good.
For example, before your patch I saw cases where the test/cmp was not emitted before the conditional branch. Your patch seems to fix that "issue" in most cases.

My only concern is that the macro-fusion mutator might be a bit too aggressive for AMD processors.
X86MacroFusion assumes that branch fusion can happen with ADD/SUB/INC/DEC too. That is okay for Intel processors, but not necessarily for AMD processors where branch fusion (as far as I remember) is limited to CMP/TEST opcodes only.
Since your patch enables that mutator for targets with FeatureMacroFusion, it would be nice to get some feedback from somebody with access to an AMD target where macro fusion is enabled (Bobcat/Jaguar doesn't do branch fusion). Perhaps @lebedev.ri can run some quick tests on BdVer2?
I don't think is a blocking issue, but in future we should revisit the logic in X86MacroFusion.


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