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[ARM] Fix select_cc lowering for fp16

Authored by olista01 on Mar 1 2019, 1:28 AM.



When lowering a select_cc node where the true and false values are of type f16, we can't use a general conditional move because the FP16 instructions do not support conditional execution. Instead, we must ensure that the condition code is one of the four supported by the VSEL instruction.

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olista01 created this revision.Mar 1 2019, 1:28 AM
SjoerdMeijer added inline comments.Mar 1 2019, 4:07 AM
2 ↗(On Diff #188863)

Just for simplicity, can we omit +fp16 here? Or do we actually need it?

For a moment I was wondering if we also need to test this with -fullfp16? I appreciate we are not testing this change anymore, but then remembered we are doing that in fp16-instructions.ll, which also contains some VSEL checks. Perhaps we can move these tests to there, or vice versa, to keep the VSEL tests together?

olista01 marked an inline comment as done.Mar 1 2019, 6:11 AM
olista01 added inline comments.
2 ↗(On Diff #188863)

I think I can remove both +fp-armv8 and +fp16.

I don't think we need to test with -fullfp16: in that case f16 isn't a legal type in the backend, so these code paths won't get hit. I copied the tests from vsel.ll and changed the types, because that looks like a comprehensive set of tests for the different condition codes.

SjoerdMeijer accepted this revision.Mar 5 2019, 12:45 AM
SjoerdMeijer added inline comments.
2 ↗(On Diff #188863)

sounds good, lgtm.

This revision is now accepted and ready to land.Mar 5 2019, 12:45 AM
This revision was automatically updated to reflect the committed changes.