[Bug c++/52792] this pointer and return pointer are passed in wrong order when ms_abi is used (x86_64)

[ktietz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52792

Kai Tietz <ktietz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |i?86-*-* x86_64-*-*

--- Comment #4 from Kai Tietz <ktietz at gcc dot gnu.org> ---
This issue isn't just about c++. It is for calling conventions using register
as arguments.

For following small sample (using ms_abi by default):

typedef struct agg { long a; long b; long c; } agg;

__declspec(dllexport) struct agg __fastcall c_fastcall(long a, long b, long c)
{
  agg r = { a, b, c};
  return r;
}

MS' compiler produces:
@c_fastcall@12:
                  push    ebp
                  mov     ebp, esp
                  mov     eax, [ebp+8]
                  mov     [eax], ecx
                  mov     ecx, [ebp+0Ch]
                  mov     [eax+4], edx
                  mov     [eax+8], ecx
                  pop     ebp
                  retn    8

but gcc produces for x86:

@c_fastcall@12:
        pushl   %ebp
        movl    %edx, (%ecx)
        movl    %ecx, %eax
        movl    %esp, %ebp
        movl    8(%ebp), %edx
        movl    %edx, 4(%ecx)
        movl    12(%ebp), %edx
        popl    %ebp
        movl    %edx, 8(%ecx)
        ret     $8

(using -O2 -fno-omit-frame-pointer)

as you can see is the aggregate pointer passed by ms via stack, but by gcc via
first argument register.