[Bug gas/30418] New: use of labels that happen to match register names or keywords

[lh_mouse at 126 dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30418

            Bug ID: 30418
           Summary: use of labels that happen to match register names or
                    keywords
           Product: binutils
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gas
          Assignee: unassigned at sourceware dot org
          Reporter: lh_mouse at 126 dot com
  Target Milestone: ---

Possible dup of https://sourceware.org/bugzilla/show_bug.cgi?id=12240

This is how MSVC handles such names:
(https://gcc.godbolt.org/z/TonjYaxqj)

```
static int* volatile rip;
static unsigned int volatile eax;

int
get_value(void)
  {
    return rip[eax];
  }
```

MSVC outputs:
```
get_value PROC                                      ; COMDAT
        mov     ecx, DWORD PTR eax
        mov     rax, QWORD PTR rip
        mov     eax, DWORD PTR [rax+rcx*4]
        ret     0
get_value ENDP
```

GCC outputs:
```
get_value:
        mov     rdx, QWORD PTR rip[rip]
        mov     eax, DWORD PTR eax[rip]
        mov     eax, DWORD PTR [rdx+rax*4]
        ret
```

In the case of MSVC, `DWORD PTR eax` is unambiguously parsed as the label `eax`
and `DWORD PTR [eax]` is unambiguously parsed as the register `eax`. The
address of all labels are always relative to RIP, but it is implied, and
brackets are not written explicitly.

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