https://issues.dlang.org/show_bug.cgi?id=17940
--- Comment #4 from github-bugzi...@puremagic.com --- Commits pushed to master at https://github.com/dlang/dmd https://github.com/dlang/dmd/commit/87cd61e4c4aca33254bacb2af735433193a51039 fix issue 17940 When generating a 1-byte mov cse on x86_64, handle the REX flag after setReg, instead of when the instruction is first created, since that's when we know if we need it. https://github.com/dlang/dmd/commit/89b0af132529d4635717fd4b16ffc300056dd1b9 Merge pull request #7252 from FeepingCreature/master fix issue 17940 - always set REX for 1-byte CSE moves on x86_64 merged-on-behalf-of: Walter Bright <walterbri...@users.noreply.github.com> --