[PATCH] D151863: [x86][MC] Fix movdir64b addressing

[Craig Topper via Phabricator via llvm-commits]

craig.topper added a comment.

MS inline assembly is parsed twice, once by clang and once by the backend.

The issue starts in the clang parsing.

I think the AH comes from this line near the end of `X86AsmParser::CreateMemForMSInlineAsm`

  // Otherwise, we set the base register to a non-zero value
  // if we don't know the actual value at this time.  This is necessary to
  // get the matching correct in some cases.

`BaseReg = BaseReg ? BaseReg : 1;`

1 happens to be the value for AH. This register is a GR64 so it fails the isMem512_GR64 check. This causes the assembly to be considered invalid.

Not sure exactly why it picks a non-zero value. I wonder if we should pick a register other than 1 based on 64bit/32bit/16bit mode?


Repository:
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  https://reviews.llvm.org/D151863/new/

https://reviews.llvm.org/D151863