Ensure correct size_t mangling on Emscripten

[kleisauke]

Emscripten defines size_t as unsigned long for both wasm32 and wasm64, mangling must therefore use m (Itanium ABI), independent of the pointer size.

Details

$ llvm-nm -pU --quiet $EMSDK/upstream/emscripten/cache/sysroot/lib/wasm32-emscripten/libc++.a | grep -e _Zn
00000001 W _Znwm
0000004a W _ZnwmRKSt9nothrow_t
00000110 W _Znam
0000011b W _ZnamRKSt9nothrow_t
00000210 W _ZnwmSt11align_val_t
0000028c W _ZnwmSt11align_val_tRKSt9nothrow_t
0000033f W _ZnamSt11align_val_t
0000034c W _ZnamSt11align_val_tRKSt9nothrow_t
$ llvm-nm -pU --quiet $EMSDK/upstream/emscripten/cache/sysroot/lib/wasm64-emscripten/libc++.a | grep -e _Zn
00000001 W _Znwm
0000004d W _ZnwmRKSt9nothrow_t
0000013b W _Znam
00000146 W _ZnamRKSt9nothrow_t
00000263 W _ZnwmSt11align_val_t
000002e2 W _ZnwmSt11align_val_tRKSt9nothrow_t
000003bd W _ZnamSt11align_val_t
000003ca W _ZnamSt11align_val_tRKSt9nothrow_t
$ emcc -dM -E - < /dev/null | grep -e __SIZEOF_SIZE_T__ -e __SIZE_TYPE__
#define __SIZEOF_SIZE_T__ 4
#define __SIZE_TYPE__ long unsigned int
$ emcc -sMEMORY64 -dM -E - < /dev/null | grep -e __SIZEOF_SIZE_T__ -e __SIZE_TYPE__
#define __SIZEOF_SIZE_T__ 8
#define __SIZE_TYPE__ long unsigned int

See also: emscripten-core/emscripten#5916.

[daanx]

Hallo, bedankt voor de PR :-) However, I think we can just add the condition (MI_INTPTR_SIZE==4 && defined(__EMSCRIPTEN__)) instead of doing the pre-processor magic? I pushed a potential fix -- let me know if it works for you. Thank you.

[kleisauke]

Great, that works for me! 👍

I initially thought consolidating these pre-processor branches would would simplify things, especially since some toolchains (like llvm-mingw) require size_t to be mangled as y, but the pre-processor magic actually ends up making things more complex.