emilio added a comment. In D72742#1822554 <https://reviews.llvm.org/D72742#1822554>, @rnk wrote:
> +@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 That seems somewhat related. This would be a similar change to the one that clang did back then, but for the bytes in the lower 32-bits when the argument is smaller than that. The ABI document, afaict, has never defined the inputs to be zero-extended. See https://groups.google.com/forum/?hl=en#!topic/x86-64-abi/E8O33onbnGQ for an old thread discussing this, and the two bugs that are referenced in the commit message (one of them fairly old). GCC does avoid the zero-extension on the caller sometimes, when not required by the language and when its optimizer finds it suitable. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D72742/new/ https://reviews.llvm.org/D72742 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
