https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53929
--- Comment #17 from LIU Hao <lh_mouse at 126 dot com> ---
Yeah. It looks to me like the Microsoft compiler doesn't actually uses the
assembler (like LLVM).
Given the C source:
```
extern int rax;
int main() { return rax; }
```
which compiled without errors:
```
> cl /O2 /c test.c /Fatest.asm
Microsoft (R) C/C++ Optimizing Compiler Version 19.29.30148 for x64
Copyright (C) Microsoft Corporation. All rights reserved.
test.c
```
and produced this assembly file
```
include listing.inc
INCLUDELIB LIBCMT
INCLUDELIB OLDNAMES
PUBLIC main
EXTRN rax:DWORD
_TEXT SEGMENT
main PROC ; COMDAT
mov eax, DWORD PTR rax
ret 0
main ENDP
_TEXT ENDS
END
```
which can't be assembled
```
> ml64 /c test.asm
Microsoft (R) Macro Assembler (x64) Version 14.29.30148.0
Copyright (C) Microsoft Corporation. All rights reserved.
Assembling: test.asm
test.asm(9) : error A2008:syntax error : rax
test.asm(16) : error A2032:invalid use of register
```
