rnk added subscribers: rjmccall, chandlerc.
rnk added a comment.

+@chandlerc @rjmccall

Didn't we work this out already when John added the alignment tracking stuff? I 
remember this bug involving libjpegturbo standalone assembly receiving a 32-bit 
argument, and then using the full 64-bit RDI register to read it, but clang 
stopped zero extending it. I thought the ABI doc was ambiguous at the time, and 
we studied GCC's behavior, and that is how we arrived at clang's current 
behavior. I am generally skeptical about changing behavior in this area just 
because the ABI doc says something now. It keeps changing. What did it say in 
the past? Shouldn't we pay more attention to that?

Found the libjpegturbo thing:
https://github.com/libjpeg-turbo/libjpeg-turbo/commit/498d9bc92fcf39124b6f08e57326944dedd2ddd6


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72742/new/

https://reviews.llvm.org/D72742



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