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[WebAssembly] Generate __clang_call_terminate for Emscripten EH #129020

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Merged
merged 3 commits into from
Feb 28, 2025
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[WebAssembly] Generate __clang_call_terminate for Emscripten EH #129020

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92861b9
[WebAssembly] Generate __clang_call_terminate for Emscripten EH
aheejin Feb 27, 2025
7e35bcf
Update clang/lib/CodeGen/ItaniumCXXABI.cpp
aheejin Feb 27, 2025
abaf565
Use wasm-unknown-emscripten triple in test
aheejin Feb 27, 2025
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9 changes: 7 additions & 2 deletions clang/lib/CodeGen/ItaniumCXXABI.cpp
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Expand Up @@ -5150,9 +5150,14 @@ WebAssemblyCXXABI::emitTerminateForUnexpectedException(CodeGenFunction &CGF,
// Itanium ABI calls __clang_call_terminate(), which __cxa_begin_catch() on
// the violating exception to mark it handled, but it is currently hard to do
// with wasm EH instruction structure with catch/catch_all, we just call
// std::terminate and ignore the violating exception as in CGCXXABI.
// std::terminate and ignore the violating exception as in CGCXXABI in Wasm EH
// and calls __clang_call_terminate only in Emscripten EH.
// TODO Consider code transformation that makes calling __clang_call_terminate
// possible.
// in Wasm EH possible.
if (Exn && !EHPersonality::get(CGF).isWasmPersonality()) {
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@dschuff dschuff Feb 27, 2025

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I assume that isWasmPersonality() is false when using emscripten EH; out of curiosity, what is the value of EHPersonality in that case?

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@aheejin aheejin Feb 27, 2025

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I didn't change anything in this case, and I checked now, and it is GNU_CPlusPlus defined here:

llvm-project/clang/lib/CodeGen/CGCleanup.h

Line 680 in f3b1849

static const EHPersonality GNU_CPlusPlus;

EHPersonality::isWasmPersonality() returns true when it is GNU_Wasm_CPlusPlus:

llvm-project/clang/lib/CodeGen/CGCleanup.h

Line 701 in f3b1849

bool isWasmPersonality() const { return this == &GNU_Wasm_CPlusPlus; }

assert(CGF.CGM.getLangOpts().CPlusPlus);
return CGF.EmitNounwindRuntimeCall(getClangCallTerminateFn(CGF.CGM), Exn);
}
return CGCXXABI::emitTerminateForUnexpectedException(CGF, Exn);
}

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12 changes: 12 additions & 0 deletions clang/test/CodeGenCXX/wasm-eh.cpp
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Expand Up @@ -6,6 +6,9 @@
// 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

// Test code generation for Wasm EH using WebAssembly EH proposal.
// (https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md)

void may_throw();
void dont_throw() noexcept;

Expand Down Expand Up @@ -381,6 +384,15 @@ void test8() {

// CHECK: unreachable

void noexcept_throw() noexcept {
throw 3;
}

// CATCH-LABEL: define void @_Z14noexcept_throwv()
// CHECK: %{{.*}} = cleanuppad within none []
// CHECK-NEXT: call void @_ZSt9terminatev()


// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -exception-model=wasm -target-feature +exception-handling -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=WARNING-DEFAULT
// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -exception-model=wasm -target-feature +exception-handling -Wwasm-exception-spec -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=WARNING-ON
// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -exception-model=wasm -target-feature +exception-handling -Wno-wasm-exception-spec -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=WARNING-OFF
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13 changes: 13 additions & 0 deletions clang/test/CodeGenCXX/wasm-em-eh.cpp
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@@ -0,0 +1,13 @@
// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s
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@dschuff dschuff Feb 27, 2025

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should this triple be wasm32-unknown-emscripten? Or do we use em-exceptions by default on all wasm triples?

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@aheejin aheejin Feb 27, 2025

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We don't do anything differently wrt EH depending on whether it is unknown or emscripten triple. But given that this test only applies to Emscripten, I changed it to wasm-unknown-emscripten.


// Test code generation for Wasm's Emscripten (JavaScript-style) EH.

void noexcept_throw() noexcept {
throw 3;
}

// CATCH-LABEL: define void @_Z14noexcept_throwv()
// CHECK: %[[LPAD:.*]] = landingpad { ptr, i32 }
// CHECK-NEXT: catch ptr null
// CHECK-NEXT: %[[EXN:.*]] = extractvalue { ptr, i32 } %[[LPAD]], 0
// CHECK-NEXT: call void @__clang_call_terminate(ptr %[[EXN]])
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