[Issue 20131] Bad codegen from inline asm LOCK CMPXCHG; possible REX prefix missing

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=20131

--- Comment #1 from Walter Bright <bugzilla at digitalmars.com> ---
Minimal test case:

  bool test() {
    asm {
        naked;
        cmpxchg [RDX], DIL;
    }
  }

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