[WebAssembly] ICE when using `__builtin_thread_pointer`

[kleisauke]

test.c:

void *f0(void)
{
#if __has_builtin(__builtin_thread_pointer)
  return __builtin_thread_pointer();
#else
  return 0;
#endif
}

$ /emsdk/upstream/bin/clang --target=wasm32 --no-standard-libraries -Wl,--no-entry -Wl,--export-all -o test.wasm test.c
fatal error: error in backend: Cannot select: intrinsic %llvm.thread.pointer
clang: error: clang frontend command failed with exit code 70 (use -v to see invocation)
clang version 20.0.0git (https:/github.com/llvm/llvm-project 3a31427224d4fa49d7ef737b21f6027dc4928ecf)
Target: wasm32
Thread model: posix
InstalledDir: /emsdk/upstream/bin
Build config: +assertions
clang: note: diagnostic msg: 
********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang: note: diagnostic msg: /tmp/test-9adbd1.c
clang: note: diagnostic msg: /tmp/test-9adbd1.sh
clang: note: diagnostic msg: 

********************

Context: emscripten-core/emscripten#21548.

[sbc100]

On the gcc side it looks like that is SH-specific builtin: https://gcc.gnu.org/onlinedocs/gcc-8.5.0/gcc/SH-Built-in-Functions.html.

Is this something that you think we should try to support, or are you just suggesting we need a better error here?

[llvmbot]

@llvm/issue-subscribers-backend-webassembly

Author: Kleis Auke Wolthuizen (kleisauke)

`test.c`: ```c void *f0(void) { return __builtin_thread_pointer(); } ``` ```console $ /emsdk/upstream/bin/clang --target=wasm32 -o test.wasm test.c fatal error: error in backend: Cannot select: intrinsic %llvm.thread.pointer clang: error: clang frontend command failed with exit code 70 (use -v to see invocation) clang version 20.0.0git (https:/github.com/llvm/llvm-project 3a31427) Target: wasm32 Thread model: posix InstalledDir: /emsdk/upstream/bin Build config: +assertions clang: note: diagnostic msg: ********************

PLEASE ATTACH THE FOLLOWING FILES TO THE BUG REPORT:
Preprocessed source(s) and associated run script(s) are located at:
clang: note: diagnostic msg: /tmp/test-9adbd1.c
clang: note: diagnostic msg: /tmp/test-9adbd1.sh
clang: note: diagnostic msg:

---

Context: https://github.com/emscripten-core/emscripten/pull/21548.
</details>

[kleisauke]

Is this something that you think we should try to support, or are you just suggesting we need a better error here?

I'm unsure whether we should support this. If it's not possible, it should likely produce an error like use of unknown builtin '__builtin_thread_pointer' and the __has_builtin(__builtin_thread_pointer) check should return false.

I've updated the reproducer accordingly.

[sbc100]

Is this something that you think we should try to support, or are you just suggesting we need a better error here?

I'm unsure whether we should support this. If it's not possible, it should likely produce an error like use of unknown builtin '__builtin_thread_pointer' and the __has_builtin(__builtin_thread_pointer) check should return false.

I've updated the reproducer accordingly.

Actually, I think we can implement fairly easily and I can so some uses for this. (I think we would just lower to global.get __tls_base).