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[driver][arm64] Set target CPU to A12 for compiler invocations that target Apple Silicon
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Authored by arphaman on Jun 26 2020, 6:26 PM.

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Summary

This change ensures that compiler invocations that target macOS, Mac Catalyst, and the iOS/tvOS/watchOS simulators for arm64 use the "apple-a12" CPU. The -mcpu option can still be used to override CPU to a newer variant.

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arphaman created this revision.Jun 26 2020, 6:26 PM
Herald added projects: Restricted Project, Restricted Project. · View Herald TranscriptJun 26 2020, 6:26 PM

@t.p.northover @ab I noticed that the use of "apple-a12" doesn't infer the right target features when we're passing in a11 or older, so that's why my test file has the INFER-A12 separate line. Do you think this is a bug? This is decided here:

else if ((A = Args.getLastArg(options::OPT_mcpu_EQ)))
  success = getAArch64ArchFeaturesFromMcpu(D, A->getValue(), Args, Features);

and CPU value isn't checked here.

I'll fix up Clang.Preprocessor::aarch64-target-features.c test this morning.

ab added a comment.Jun 30 2020, 7:23 AM

@t.p.northover @ab I noticed that the use of "apple-a12" doesn't infer the right target features when we're passing in a11 or older, so that's why my test file has the INFER-A12 separate line. Do you think this is a bug? This is decided here:

else if ((A = Args.getLastArg(options::OPT_mcpu_EQ)))
  success = getAArch64ArchFeaturesFromMcpu(D, A->getValue(), Args, Features);

and CPU value isn't checked here.

Interesting. Does it even pass the newer CPU then? If so I imagine the features are still enabled in the backend because of the cpu, so this would only affect frontend behavior (e.g., preprocessor macros, which might in turn affect some intrinsic headers, etc..). Either way, I agree it's a bug

But the apple-a12 floor isn't a hard requirement here (unlike e.g., arm64e where we'll fail to compile without certain features), so I'm tempted to avoid these shenanigans entirely and let users specify what they want. What do you think?

We're seeing some build warnings in ffmpeg due to this not being in yet. Could you try to land it soon?

dexonsmith resigned from this revision.Tue, Oct 6, 3:22 PM
arphaman updated this revision to Diff 299564.Tue, Oct 20, 11:32 PM

Don't try to fallback to the "apple-a12" cpu type when the user explicitly specifies an older cpu. The default is still "apple-a12".

dexonsmith accepted this revision.Wed, Oct 21, 4:31 AM

Updated patch LGTM.

This revision is now accepted and ready to land.Wed, Oct 21, 4:31 AM