[WebAssembly] Change size_t to `unsigned long`

[sunfish]

Summary

Currently wasm's size_t is unsigned int for compatibility with asm.js and Emscripten's library code; see the patch for details.

Changing it to unsigned long (which is also 32-bit on wasm32) would make it the same type as wasm64 (where unsigned long is 64-bit), which would eliminate the most common cause for mangled names being different between wasm32 and wasm64. For example, export lists containing symbol names could often be the same between wasm32 and wasm64.

Even though the ABI won't be officially stable for a while, increasing numbers of tools are looking to interoperate with LLVM's output, and core details like the size_t type may become inconvenient to change in the future.

This patch aims to remain compatible with current Emscripten integration by making the change only in the wasm32-unknown-unknown-wasm triple, so it won't affect the s2wasm path, which uses the wasm32-unknown-unknown-elf triple. It would be something that would need to be handled if Emscripten wants to start using the wasm32-unknown-unknown-wasm triple through.

[sunfish]

This updates the patch to make size_t be unsigned long unconditionally, corresponding with the proposed patch to Emscripten here which changes it for asm.js as well.

[sunfish]

Rebase for upstream changes.

[dschuff]

LGTM FTR, as long as we coordinate when this lands with emscripten.

[sunfish]

The LLVM patch, the emscripten-fastcomp-clang patch, and the emscripten patch are now all updated and in sync.

[andrewrk]

Is there anything stopping this from landing in svn?

[sunfish]

We want to coordinate landing this with corresponding changes in Emscripten. Since this is an ABI change, Emscripten needs to figure out how to manage it. See here for ongoing discussion.

[sunfish]

I've now refreshed the emscripten patches and am hoping they can land soon.

[sbc100]

I'm running into an issue with an internal codebase that assumes that size_t is equivalent to either int32_t or int64_t which this change invalidates.

After this change we have:
size_t -> long
int32_t -> int
int64_t -> ling long int.

e.g.:

#include <inttypes.h>
#include <stdlib.h>

int func(int32_t* f) {
  return 1;
}

int func(int64_t* f) {
  return 2;
}

int main() {
  size_t a = 0 ;
  return func(&a);
}

This generates the following error after this change:

./bin/clang --target=wasm32 -c ./test.cpp 
./test.cpp:14:10: error: no matching function for call to 'func'
  return func(&a);
         ^~~~
./test.cpp:4:5: note: candidate function not viable: no known conversion from 'size_t *' (aka 'unsigned long *') to 'int32_t *'
      (aka 'int *') for 1st argument
int func(int32_t* f) {
    ^
./test.cpp:8:5: note: candidate function not viable: no known conversion from 'size_t *' (aka 'unsigned long *') to 'int64_t *'
      (aka 'long long *') for 1st argument
int func(int64_t* f) {
    ^
1 error generated.

[sbc100]

Should we change int32_t as well? Or does the above code just need fixing? I'm a little concerned because this code is very portable which implies that WebAssembly might be doing something unusual here.

[sunfish]

Is this related to the issue reported in the thread here?

[sbc100]

In D40526#1192688, @sunfish wrote:

Is this related to the issue reported in the thread here?

Ah yes, I'll follow up there.

[azakai]

This has also shown up in a game engine middleware codebase, so it may be a
broader issue - people seem to assume size_t is one of the int*_t types.

lib/Basic/Targets/WebAssembly.h

explicit WebAssemblyTargetInfo(const llvm::Triple &T, const TargetOptions &)
     NoAsmVariants = true;
     SuitableAlign = 128;
     LargeArrayMinWidth = 128;
     LargeArrayAlign = 128;
     SimdDefaultAlign = 128;
     SigAtomicType = SignedLong;
     LongDoubleWidth = LongDoubleAlign = 128;
     LongDoubleFormat = &llvm::APFloat::IEEEquad();
-    SizeType = UnsignedInt;
-    PtrDiffType = SignedInt;
-    IntPtrType = SignedInt;
+    // size_t being unsigned long for both wasm32 and wasm64 makes mangled names
+    // more consistent between the two.
+    SizeType = UnsignedLong;
+    PtrDiffType = SignedLong;
+    IntPtrType = SignedLong;
   }
 
 protected:
   void getTargetDefines(const LangOptions &Opts,
                         MacroBuilder &Builder) const override;
 
 private:
   bool

test/Preprocessor/init.c

 // WEBASSEMBLY32-NEXT:#define __INT8_MAX__ 127
 // WEBASSEMBLY32-NEXT:#define __INT8_TYPE__ signed char
 // WEBASSEMBLY32-NEXT:#define __INTMAX_C_SUFFIX__ LL
 // WEBASSEMBLY32-NEXT:#define __INTMAX_FMTd__ "lld"
 // WEBASSEMBLY32-NEXT:#define __INTMAX_FMTi__ "lli"
 // WEBASSEMBLY32-NEXT:#define __INTMAX_MAX__ 9223372036854775807LL
 // WEBASSEMBLY32-NEXT:#define __INTMAX_TYPE__ long long int
 // WEBASSEMBLY32-NEXT:#define __INTMAX_WIDTH__ 64
-// WEBASSEMBLY32-NEXT:#define __INTPTR_FMTd__ "d"
-// WEBASSEMBLY32-NEXT:#define __INTPTR_FMTi__ "i"
-// WEBASSEMBLY32-NEXT:#define __INTPTR_MAX__ 2147483647
-// WEBASSEMBLY32-NEXT:#define __INTPTR_TYPE__ int
+// WEBASSEMBLY32-NEXT:#define __INTPTR_FMTd__ "ld"
+// WEBASSEMBLY32-NEXT:#define __INTPTR_FMTi__ "li"
+// WEBASSEMBLY32-NEXT:#define __INTPTR_MAX__ 2147483647L
+// WEBASSEMBLY32-NEXT:#define __INTPTR_TYPE__ long int
 // WEBASSEMBLY32-NEXT:#define __INTPTR_WIDTH__ 32
 // WEBASSEMBLY32-NEXT:#define __INT_FAST16_FMTd__ "hd"
 // WEBASSEMBLY32-NEXT:#define __INT_FAST16_FMTi__ "hi"
 // WEBASSEMBLY32-NEXT:#define __INT_FAST16_MAX__ 32767
 // WEBASSEMBLY32-NEXT:#define __INT_FAST16_TYPE__ short
 // WEBASSEMBLY32-NEXT:#define __INT_FAST32_FMTd__ "d"
 // WEBASSEMBLY32-NEXT:#define __INT_FAST32_FMTi__ "i"
 // WEBASSEMBLY32-NEXT:#define __INT_FAST32_MAX__ 2147483647

 // WEBASSEMBLY32-NEXT:#define __OPENCL_MEMORY_SCOPE_SUB_GROUP 4
 // WEBASSEMBLY32-NEXT:#define __OPENCL_MEMORY_SCOPE_WORK_GROUP 1
 // WEBASSEMBLY32-NEXT:#define __OPENCL_MEMORY_SCOPE_WORK_ITEM 0
 // WEBASSEMBLY32-NEXT:#define __ORDER_BIG_ENDIAN__ 4321
 // WEBASSEMBLY32-NEXT:#define __ORDER_LITTLE_ENDIAN__ 1234
 // WEBASSEMBLY32-NEXT:#define __ORDER_PDP_ENDIAN__ 3412
 // WEBASSEMBLY32-NEXT:#define __POINTER_WIDTH__ 32
 // WEBASSEMBLY32-NEXT:#define __PRAGMA_REDEFINE_EXTNAME 1
-// WEBASSEMBLY32-NEXT:#define __PTRDIFF_FMTd__ "d"
-// WEBASSEMBLY32-NEXT:#define __PTRDIFF_FMTi__ "i"
-// WEBASSEMBLY32-NEXT:#define __PTRDIFF_MAX__ 2147483647
-// WEBASSEMBLY32-NEXT:#define __PTRDIFF_TYPE__ int
+// WEBASSEMBLY32-NEXT:#define __PTRDIFF_FMTd__ "ld"
+// WEBASSEMBLY32-NEXT:#define __PTRDIFF_FMTi__ "li"
+// WEBASSEMBLY32-NEXT:#define __PTRDIFF_MAX__ 2147483647L
+// WEBASSEMBLY32-NEXT:#define __PTRDIFF_TYPE__ long int
 // WEBASSEMBLY32-NEXT:#define __PTRDIFF_WIDTH__ 32
 // WEBASSEMBLY32-NOT:#define __REGISTER_PREFIX__
 // WEBASSEMBLY32-NEXT:#define __SCHAR_MAX__ 127
 // WEBASSEMBLY32-NEXT:#define __SHRT_MAX__ 32767
 // WEBASSEMBLY32-NEXT:#define __SIG_ATOMIC_MAX__ 2147483647L
 // WEBASSEMBLY32-NEXT:#define __SIG_ATOMIC_WIDTH__ 32
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_DOUBLE__ 8
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_FLOAT__ 4
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_INT128__ 16
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_INT__ 4
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_LONG_DOUBLE__ 16
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_LONG_LONG__ 8
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_LONG__ 4
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_POINTER__ 4
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_PTRDIFF_T__ 4
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_SHORT__ 2
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_SIZE_T__ 4
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_WCHAR_T__ 4
 // WEBASSEMBLY32-NEXT:#define __SIZEOF_WINT_T__ 4
-// WEBASSEMBLY32-NEXT:#define __SIZE_FMTX__ "X"
-// WEBASSEMBLY32-NEXT:#define __SIZE_FMTo__ "o"
-// WEBASSEMBLY32-NEXT:#define __SIZE_FMTu__ "u"
-// WEBASSEMBLY32-NEXT:#define __SIZE_FMTx__ "x"
-// WEBASSEMBLY32-NEXT:#define __SIZE_MAX__ 4294967295U
-// WEBASSEMBLY32-NEXT:#define __SIZE_TYPE__ unsigned int
+// WEBASSEMBLY32-NEXT:#define __SIZE_FMTX__ "lX"
+// WEBASSEMBLY32-NEXT:#define __SIZE_FMTo__ "lo"
+// WEBASSEMBLY32-NEXT:#define __SIZE_FMTu__ "lu"
+// WEBASSEMBLY32-NEXT:#define __SIZE_FMTx__ "lx"
+// WEBASSEMBLY32-NEXT:#define __SIZE_MAX__ 4294967295UL
+// WEBASSEMBLY32-NEXT:#define __SIZE_TYPE__ long unsigned int
 // WEBASSEMBLY32-NEXT:#define __SIZE_WIDTH__ 32
 // WEBASSEMBLY32-NEXT:#define __STDC_HOSTED__ 0
 // WEBASSEMBLY32-NOT:#define __STDC_MB_MIGHT_NEQ_WC__
 // WEBASSEMBLY32-NOT:#define __STDC_NO_ATOMICS__
 // WEBASSEMBLY32-NOT:#define __STDC_NO_COMPLEX__
 // WEBASSEMBLY32-NOT:#define __STDC_NO_VLA__
 // WEBASSEMBLY32-NOT:#define __STDC_NO_THREADS__
 // WEBASSEMBLY32-NEXT:#define __STDC_UTF_16__ 1

 // WEBASSEMBLY32-NEXT:#define __UINTMAX_C_SUFFIX__ ULL
 // WEBASSEMBLY32-NEXT:#define __UINTMAX_FMTX__ "llX"
 // WEBASSEMBLY32-NEXT:#define __UINTMAX_FMTo__ "llo"
 // WEBASSEMBLY32-NEXT:#define __UINTMAX_FMTu__ "llu"
 // WEBASSEMBLY32-NEXT:#define __UINTMAX_FMTx__ "llx"
 // WEBASSEMBLY32-NEXT:#define __UINTMAX_MAX__ 18446744073709551615ULL
 // WEBASSEMBLY32-NEXT:#define __UINTMAX_TYPE__ long long unsigned int
 // WEBASSEMBLY32-NEXT:#define __UINTMAX_WIDTH__ 64
-// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTX__ "X"
-// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTo__ "o"
-// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTu__ "u"
-// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTx__ "x"
-// WEBASSEMBLY32-NEXT:#define __UINTPTR_MAX__ 4294967295U
-// WEBASSEMBLY32-NEXT:#define __UINTPTR_TYPE__ unsigned int
+// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTX__ "lX"
+// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTo__ "lo"
+// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTu__ "lu"
+// WEBASSEMBLY32-NEXT:#define __UINTPTR_FMTx__ "lx"
+// WEBASSEMBLY32-NEXT:#define __UINTPTR_MAX__ 4294967295UL
+// WEBASSEMBLY32-NEXT:#define __UINTPTR_TYPE__ long unsigned int
 // WEBASSEMBLY32-NEXT:#define __UINTPTR_WIDTH__ 32
 // WEBASSEMBLY32-NEXT:#define __UINT_FAST16_FMTX__ "hX"
 // WEBASSEMBLY32-NEXT:#define __UINT_FAST16_FMTo__ "ho"
 // WEBASSEMBLY32-NEXT:#define __UINT_FAST16_FMTu__ "hu"
 // WEBASSEMBLY32-NEXT:#define __UINT_FAST16_FMTx__ "hx"
 // WEBASSEMBLY32-NEXT:#define __UINT_FAST16_MAX__ 65535
 // WEBASSEMBLY32-NEXT:#define __UINT_FAST16_TYPE__ unsigned short
 // WEBASSEMBLY32-NEXT:#define __UINT_FAST32_FMTX__ "X"