[Bug c++/103635] New: size_t and uintptr_t have wrong sizes with x86_64-w64-mingw32-g++ -mabi=sysv

[mark at harmstone dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103635

            Bug ID: 103635
           Summary: size_t and uintptr_t have wrong sizes with
                    x86_64-w64-mingw32-g++ -mabi=sysv
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mark at harmstone dot com
  Target Milestone: ---

When you add the option -mabi=sysv to mingw for amd64, it changes size_t and
uintptr_t from 64 to 32 bits.

Minimal example:

tmp.cpp:
#include <stddef.h>
static_assert(sizeof(size_t) == 8, "!");
static_assert(sizeof(uintptr_t) == 8, "!");

Working:
x86_64-pc-linux-gnu-g++ -mabi=ms -c tmp.cpp
x86_64-pc-linux-gnu-g++ -mabi=sysv -c tmp.cpp
x86_64-pc-cygwin-g++ -mabi=ms -c tmp.cpp
x86_64-pc-cygwin-g++ -mabi=sysv -c tmp.cpp
x86_64-w64-mingw32-g++ -mabi=ms -c tmp.cpp

Not working:
x86_64-w64-mingw32-g++ -mabi=sysv -c tmp.cpp
tmp.cpp:2:30: error: static assertion failed: !
    2 | static_assert(sizeof(size_t) == 8, "!");
      |               ~~~~~~~~~~~~~~~^~~~
tmp.cpp:3:33: error: static assertion failed: !
    3 | static_assert(sizeof(uintptr_t) == 8, "!");
      | 

My hunch is that perhaps GCC is assuming that long is the same size as a
pointer, which it's not on Windows. The SysV specs say that size_t is
equivalent to unsigned long on LP64 (but unsurprisingly doesn't mention the
LLP64 that Windows uses).

The practical problem this causes is that you can't #include <string> on mingw
with -mabi=sysv, as _mm_malloc amongst others uses size_t to do pointer
arithmetic.