[clang] [WebAssembly] Define __USING_WASM_EXCEPTIONS__ for -fwasm-exceptions (PR #92604)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Heejin Ahn (aheejin)

<details>
<summary>Changes</summary>

When using other specific exception options in Clang, such as `-fseh-exceptions` or `-fsjlj-exceptions`, Clang defines a corresponding preprocessor such as `-D__USING_SJLJ_EXCEPTIONS__`. Emscripten does that in our own build system:
https://github.com/emscripten-core/emscripten/blob/7dcd7f40749918e141dc33397d2f4311dd80637a/tools/system_libs.py#L1577-L1578

But to make Wasm EH usable in non-Emscripten toolchain, this has to be defined somewhere else. This PR makes Wasm EH consistent with other exception scheme by letting it defined by Clang depending on the exception option.

---
Full diff: https://github.com/llvm/llvm-project/pull/92604.diff


2 Files Affected:

- (modified) clang/lib/Frontend/InitPreprocessor.cpp (+2) 
- (modified) clang/test/CodeGenCXX/wasm-eh.cpp (+4) 


``````````diff
diff --git a/clang/lib/Frontend/InitPreprocessor.cpp b/clang/lib/Frontend/InitPreprocessor.cpp
index c1d209466ffe5..3cc85ff502776 100644
--- a/clang/lib/Frontend/InitPreprocessor.cpp
+++ b/clang/lib/Frontend/InitPreprocessor.cpp
@@ -1006,6 +1006,8 @@ static void InitializePredefinedMacros(const TargetInfo &TI,
   else if (LangOpts.hasDWARFExceptions() &&
            (TI.getTriple().isThumb() || TI.getTriple().isARM()))
     Builder.defineMacro("__ARM_DWARF_EH__");
+  else if (LangOpts.hasWasmExceptions())
+    Builder.defineMacro("__USING_WASM_EXCEPTIONS__");
 
   if (LangOpts.Deprecated)
     Builder.defineMacro("__DEPRECATED");
diff --git a/clang/test/CodeGenCXX/wasm-eh.cpp b/clang/test/CodeGenCXX/wasm-eh.cpp
index af023f52191b9..09588985d4e74 100644
--- a/clang/test/CodeGenCXX/wasm-eh.cpp
+++ b/clang/test/CodeGenCXX/wasm-eh.cpp
@@ -1,4 +1,8 @@
 // REQUIRES: webassembly-registered-target
+
+// RUN: %clang -E -dM %s -target wasm32-unknown-unknown -fwasm-exceptions | FileCheck %s -check-prefix PREPROCESSOR
+// PREPROCESSOR: #define __USING_WASM_EXCEPTIONS__ 1
+
 // RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -mllvm -wasm-enable-eh -exception-model=wasm -target-feature +exception-handling -emit-llvm -o - -std=c++11 | FileCheck %s
 // RUN: %clang_cc1 %s -triple wasm64-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -mllvm -wasm-enable-eh -exception-model=wasm -target-feature +exception-handling -emit-llvm -o - -std=c++11 | FileCheck %s
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/92604