[PATCH] D102791: [WebAssembly] Warn on exception spec for Emscripten EH

[Heejin Ahn via Phabricator via cfe-commits]

aheejin created this revision.
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It turns out we have not correctly supported exception spec all along in
Emscripten EH. Emscripten EH supports `throw()` but not `throw` with
types. See https://bugs.llvm.org/show_bug.cgi?id=50396.

Wasm EH also only supports `throw()` but not `throw` with types, and we
have been printing a warning message for the latter. This prints the
same warning message for `throw` with types when Emscripten EH is used,
or more precisely, when Wasm EH is not used. (So this will print the
warning messsage even when `-fno-exceptions` is used but I think that
should be fine. It's cumbersome to do a complilcated option checking in
CGException.cpp and options checkings are mostly done in elsewhere.)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D102791

Files:
  clang/lib/CodeGen/CGException.cpp
  clang/test/CodeGenCXX/wasm-eh.cpp


Index: clang/test/CodeGenCXX/wasm-eh.cpp
===================================================================
--- clang/test/CodeGenCXX/wasm-eh.cpp
+++ clang/test/CodeGenCXX/wasm-eh.cpp
@@ -381,7 +381,7 @@
 // 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
-// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=NOT-WASM-EH
+// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s --check-prefix=EM-EH-WARNING
 
 // Wasm EH ignores dynamic exception specifications with types at the moment.
 // This is controlled by -Wwasm-exception-spec, which is on by default. This
@@ -392,7 +392,7 @@
 // WARNING-DEFAULT: warning: dynamic exception specifications with types are currently ignored in wasm
 // WARNING-ON: warning: dynamic exception specifications with types are currently ignored in wasm
 // WARNING-OFF-NOT: warning: dynamic exception specifications with types are currently ignored in wasm
-// NOT-WASM-EH-NOT: warning: dynamic exception specifications with types are currently ignored in wasm
+// EM-EH-WARNING: warning: dynamic exception specifications with types are currently ignored in wasm
 
 // Wasm curremtly treats 'throw()' in the same way as 'noexept'. Check if the
 // same warning message is printed as if when a 'noexcept' function throws.
Index: clang/lib/CodeGen/CGException.cpp
===================================================================
--- clang/lib/CodeGen/CGException.cpp
+++ clang/lib/CodeGen/CGException.cpp
@@ -473,9 +473,9 @@
     // encode these in an object file but MSVC doesn't do anything with it.
     if (getTarget().getCXXABI().isMicrosoft())
       return;
-    // In wasm we currently treat 'throw()' in the same way as 'noexcept'. In
+    // In Wasm EH we currently treat 'throw()' in the same way as 'noexcept'. In
     // case of throw with types, we ignore it and print a warning for now.
-    // TODO Correctly handle exception specification in wasm
+    // TODO Correctly handle exception specification in Wasm EH
     if (CGM.getLangOpts().hasWasmExceptions()) {
       if (EST == EST_DynamicNone)
         EHStack.pushTerminate();
@@ -485,6 +485,19 @@
             << FD->getExceptionSpecSourceRange();
       return;
     }
+    // Currently Emscripten EH only handles 'throw()' but not 'throw' with
+    // types. 'throw()' handling will be done in JS glue code so we don't need
+    // to do anything in that case. Just print a warning message in case of
+    // throw with types.
+    // TODO Correctly handle exception specification in Emscripten EH
+    if (getTarget().getCXXABI() == TargetCXXABI::WebAssembly &&
+        CGM.getLangOpts().getExceptionHandling() ==
+            LangOptions::ExceptionHandlingKind::None &&
+        EST == EST_Dynamic)
+      CGM.getDiags().Report(D->getLocation(),
+                            diag::warn_wasm_dynamic_exception_spec_ignored)
+          << FD->getExceptionSpecSourceRange();
+
     unsigned NumExceptions = Proto->getNumExceptions();
     EHFilterScope *Filter = EHStack.pushFilter(NumExceptions);
 


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