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[AVR] Use @earlyclobber instead of register scavenging
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Authored by aykevl on Aug 13 2022, 1:04 PM.

Details

Summary

The code to support the case when the register allocator has assigned
the same register to the src and the dst register operand isn't actually
needed:

  • LDWRdPtr and LDDWRdPtrQ have an @earlyclobber on the output register, so the register allocator will make sure to allocate a different register for the output register.
  • LDDWRdYQ does not have an @earlyclobber, but the pointer register is the fixed Y register which is reserved. The register allocator won't use reserved registers for the output value.

This removes a special case in the code that makes the pseudo
instruction expansion pass more complicated than it needs to be.

I tested this locally with TinyGo and all test cases still pass, so that gives some confidence that this doesn't break anything.

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Event Timeline

aykevl created this revision.Aug 13 2022, 1:04 PM
Herald added a project: Restricted Project. · View Herald TranscriptAug 13 2022, 1:04 PM
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aykevl requested review of this revision.Aug 13 2022, 1:04 PM
Herald added a project: Restricted Project. · View Herald TranscriptAug 13 2022, 1:04 PM
aykevl edited the summary of this revision. (Show Details)Aug 13 2022, 1:05 PM

I forgot about D117957. This is a shorter version that doesn't include the LPM/ELPM changes.

This revision is now accepted and ready to land.Aug 13 2022, 7:46 PM
This revision was automatically updated to reflect the committed changes.