[all-commits] [llvm/llvm-project] da85b2: [WebAssembly] Generate __clang_call_terminate for ...

[Heejin Ahn via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: da85b2a86403fb4bf065a4463691914f444bc07a
      https://github.com/llvm/llvm-project/commit/da85b2a86403fb4bf065a4463691914f444bc07a
  Author: Heejin Ahn <aheejin at gmail.com>
  Date:   2025-02-27 (Thu, 27 Feb 2025)

  Changed paths:
    M clang/lib/CodeGen/ItaniumCXXABI.cpp
    M clang/test/CodeGenCXX/wasm-eh.cpp
    A clang/test/CodeGenCXX/wasm-em-eh.cpp

  Log Message:
  -----------
  [WebAssembly] Generate __clang_call_terminate for Emscripten EH (#129020)

When an exception thrown ends up calling `std::terminate`, for example,
because an exception is thrown within a `noexcept` function or an
exception is thrown from `__cxa_end_catch` during handling the previous
exception, the libc++abi spec says we are supposed to call
`__cxa_begin_catch` before `std::terminate`:
https://libcxxabi.llvm.org/spec.html
> When the personality routine encounters a termination condition, it
will call `__cxa_begin_catch()` to mark the exception as handled and
then call `terminate()`, which shall not return to its caller.

The default Itanium ABI generates a call to `__clang_call_terminate()`,
which is a function that calls `__cxa_begin_catch` and then
`std::terminate`:
```ll
define void @__clang_call_terminate(ptr noundef %0) {
  %2 = call ptr @__cxa_begin_catch(ptr %0)
  call void @_ZSt9terminatev()
  unreachable
}
```

But we replaced this with just a call to `std::terminate` in
https://github.com/llvm/llvm-project/commit/561abd83ffecc8d4ba8fcbbbcadb31efc55985c2
because this caused some tricky transformation problems for Wasm EH. The
detailed explanation why is in the commit description, but the summary
is for Wasm EH it needed a `try` with both `catch` and `catch_all` and
it was tricky to deal with.

But that commit replaced `__clang_call_terminate` with `std::terminate`
for all Wasm programs and not only the ones that use Wasm EH. So
Emscripten EH was also affected by that commit. Emscripten EH is not
able to catch foreign exceptions anyway, so this is unnecessary
compromise.

This makes we use `__clang_call_terminate` as in the default Itanium EH
for Emscripten EH. We may later fix Wasm EH too but that requires more
efforts in the backend.

Related issue:
https://github.com/emscripten-core/emscripten/issues/23720



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