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[X86] Separate CPU Feature lists in X86.td between architecture features and tuning features
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Authored by craig.topper on Wed, Jul 29, 11:29 AM.

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Summary

After the recent change to the tuning settings for pentium4 to improve our default 32-bit behavior, I've decided to see about implementing -mtune support. This way we could have a default architecture CPU of "pentium4" or "x86-64" and a default tuning cpu of "generic". And we could change our "pentium4" tuning settings back to what they were before.

As a step to supporting this, this patch separates all of the features lists for the CPUs into 2 lists. I'm using the Proc class and a new ProcModel class to concat the 2 lists before passing to the target independent ProcessorModel. Future work to truly support mtune would change ProcessorModel to take 2 lists separately. I've diffed the X86GenSubtargetInfo.inc file before and after this patch to ensure that the final feature list for the CPUs isn't changed.

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Event Timeline

craig.topper created this revision.Wed, Jul 29, 11:29 AM
Herald added a project: Restricted Project. · View Herald TranscriptWed, Jul 29, 11:29 AM
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craig.topper requested review of this revision.Wed, Jul 29, 11:29 AM
craig.topper added inline comments.
llvm/lib/Target/X86/X86.td
621

Oops. I left some tuning flags in here. I'll fix and upload a new patch soon.

Fixed BDWAdditionalFeatures

RKSimon added inline comments.Wed, Jul 29, 11:35 AM
llvm/lib/Target/X86/X86.td
562

I keep forgetting to ask - why do targets without AVX implement FeatureInsertVZEROUPPER?

craig.topper added inline comments.Wed, Jul 29, 11:58 AM
llvm/lib/Target/X86/X86.td
562

It starts with an assumption that "-mavx" without a -march should insert vzeroupper. Since in that case the CPU will be pentium4 or x86-64 so those CPUs need the feature. Maybe also i486 or i686 if you're on the BSD that uses those as the default 32-bit CPU. After that it was just to apply consistent behavior if you wrote something like "-march=nehalem -mavx" for some reason.

RKSimon accepted this revision.Thu, Jul 30, 12:43 PM

LGTM - thanks for taking this on!

This revision is now accepted and ready to land.Thu, Jul 30, 12:43 PM