https://github.com/aheejin updated https://github.com/llvm/llvm-project/pull/129020
>From 92861b903905d4f3d2fa39772033282b2dbad758 Mon Sep 17 00:00:00 2001 From: Heejin Ahn <ahee...@gmail.com> Date: Thu, 27 Feb 2025 03:09:45 +0000 Subject: [PATCH 1/2] [WebAssembly] Generate __clang_call_terminate for Emscripten EH 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 needs 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 --- clang/lib/CodeGen/ItaniumCXXABI.cpp | 9 +++++++-- clang/test/CodeGenCXX/wasm-eh.cpp | 12 ++++++++++++ clang/test/CodeGenCXX/wasm-em-eh.cpp | 13 +++++++++++++ 3 files changed, 32 insertions(+), 2 deletions(-) create mode 100644 clang/test/CodeGenCXX/wasm-em-eh.cpp diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp index bcd171724c41d..f3ffa0b2e84c1 100644 --- a/clang/lib/CodeGen/ItaniumCXXABI.cpp +++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp @@ -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()) { + assert(CGF.CGM.getLangOpts().CPlusPlus); + return CGF.EmitNounwindRuntimeCall(getClangCallTerminateFn(CGF.CGM), Exn); + } return CGCXXABI::emitTerminateForUnexpectedException(CGF, Exn); } diff --git a/clang/test/CodeGenCXX/wasm-eh.cpp b/clang/test/CodeGenCXX/wasm-eh.cpp index 9dc15633bfed9..e8797794e7c1e 100644 --- a/clang/test/CodeGenCXX/wasm-eh.cpp +++ b/clang/test/CodeGenCXX/wasm-eh.cpp @@ -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; @@ -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 diff --git a/clang/test/CodeGenCXX/wasm-em-eh.cpp b/clang/test/CodeGenCXX/wasm-em-eh.cpp new file mode 100644 index 0000000000000..9b2ccb2103bbc --- /dev/null +++ b/clang/test/CodeGenCXX/wasm-em-eh.cpp @@ -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 + +// 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]]) >From 7e35bcf4f795b4b374b31fa5866b4b00d99ebe0c Mon Sep 17 00:00:00 2001 From: Heejin Ahn <ahee...@gmail.com> Date: Thu, 27 Feb 2025 14:53:24 -0800 Subject: [PATCH 2/2] Update clang/lib/CodeGen/ItaniumCXXABI.cpp Co-authored-by: Derek Schuff <dsch...@chromium.org> --- clang/lib/CodeGen/ItaniumCXXABI.cpp | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp index f3ffa0b2e84c1..a84412bd5c045 100644 --- a/clang/lib/CodeGen/ItaniumCXXABI.cpp +++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp @@ -5151,7 +5151,7 @@ WebAssemblyCXXABI::emitTerminateForUnexpectedException(CodeGenFunction &CGF, // 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 in Wasm EH - // and calls __clang_call_terminate only in Emscripten EH. + // and call __clang_call_terminate only in Emscripten EH. // TODO Consider code transformation that makes calling __clang_call_terminate // in Wasm EH possible. if (Exn && !EHPersonality::get(CGF).isWasmPersonality()) { _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
