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[GlobalISel] Support for inlining memcpy, memset and memmove calls
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Authored by aemerson on Tue, Jul 23, 2:25 PM.

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Summary

This introduces a new family of combiner helper routines that re-use the target specific cost model from SelectionDAG, and generate inline implementations of the memcpy family of intrinsics.

The combines are only enabled at optimization levels higher than -O0, and give very substantial performance improvements.

Diff Detail

Repository
rL LLVM

Event Timeline

aemerson created this revision.Tue, Jul 23, 2:25 PM
paquette added inline comments.Tue, Jul 23, 3:15 PM
llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
442 ↗(On Diff #211355)

de morgan?

550–553 ↗(On Diff #211355)

Could this part be pulled out into the caller? It shows up in each of the optimization functions and does the same thing. Then this could just assert on KnownLen?

580–586 ↗(On Diff #211355)

I feel like this could be a helper, since it appears in a few of these functions?

692–712 ↗(On Diff #211355)

Could this be a helper, since it appears in two of these functions?

825 ↗(On Diff #211355)

Is this worth collecting a statistic for? Does SDAG have something like that for comparison?

838 ↗(On Diff #211355)

If you init this to Src, then you can kill the if and make the else a if (CurrOffset != 0)?

Then you can also scope Offset into the new if.

880 ↗(On Diff #211355)

initialize to false?

885–886 ↗(On Diff #211355)

Should we just assert that we have one of these IDs instead of putting them in a switch?

907–909 ↗(On Diff #211355)

Could probably check this before entering the switch

aemerson marked 8 inline comments as done.Tue, Jul 23, 4:04 PM
aemerson added inline comments.
llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
442 ↗(On Diff #211355)

Done.

550–553 ↗(On Diff #211355)

Sure.

580–586 ↗(On Diff #211355)

I'm gonna disagree here because the blocks use 6 variables from the function scope, so by the time we plumb through all the arguments we're going to end up with a similar amount of code duplication, with additional indirection.

825 ↗(On Diff #211355)

I don't think SelectionDAG does either. I can add it if required but these are so common I'm not sure what the benefit will be to have them.

838 ↗(On Diff #211355)

Ok.

880 ↗(On Diff #211355)

Ok.

885–886 ↗(On Diff #211355)

I'll simplify it a bit.

907–909 ↗(On Diff #211355)

Ok.

aemerson updated this revision to Diff 211375.Tue, Jul 23, 4:15 PM

Addressed most of the comments.

paquette accepted this revision.Wed, Jul 24, 10:13 AM

LGTM with some comments

llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
428 ↗(On Diff #211375)

s/an partial/a partial/

595 ↗(On Diff #211375)

Can we have some documentation for what the memset is being optimized to and what the stores should look like?

(same for the other optimize functions)

880 ↗(On Diff #211375)

IIRC this returns an int64_t and can return negative values; should we check that this is positive? Or is it not possible for it to be negative?

882–885 ↗(On Diff #211375)

should we assert that KnownLen != 0 in the optimize functions now?

This revision is now accepted and ready to land.Wed, Jul 24, 10:13 AM
aemerson marked 2 inline comments as done.Wed, Jul 24, 3:02 PM
aemerson added inline comments.
llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
880 ↗(On Diff #211375)

I don't think it's possible to specify a "negative" length, if it somehow happened then it would be UB I think.

882–885 ↗(On Diff #211375)

Will do.

This revision was automatically updated to reflect the committed changes.