[WebAssembly] Handle exception specifications

Summary:
Wasm currently does not fully handle exception specifications. Rather
than crashing,
- This treats `throw()` in the same way as `noexcept`.
- This ignores and prints a warning for `throw(type, ..)`, for a
  temporary measure. This warning is controlled by
  `-Wwasm-exception-spec`, which is on by default. You can suppress the
  warning by using `-Wno-wasm-exception-spec`.

Reviewers: dschuff

Subscribers: sbc100, jgravelle-google, sunfish, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D80061

1 files changed, 21 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGException.cpp b/clang/lib/CodeGen/CGException.cpp
index a5dae1b..d821eb2 100644
--- a/clang/lib/CodeGen/CGException.cpp
+++ b/clang/lib/CodeGen/CGException.cpp
@@ -20,6 +20,7 @@
 #include "clang/AST/StmtCXX.h"
 #include "clang/AST/StmtObjC.h"
 #include "clang/AST/StmtVisitor.h"
+#include "clang/Basic/DiagnosticSema.h"
 #include "clang/Basic/TargetBuiltins.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
@@ -468,6 +469,18 @@ void CodeGenFunction::EmitStartEHSpec(const Decl *D) {
     // 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
+    // case of throw with types, we ignore it and print a warning for now.
+    // TODO Correctly handle exception specification in wasm
+    if (getTarget().getCXXABI() == TargetCXXABI::WebAssembly) {
+      if (EST == EST_DynamicNone)
+        EHStack.pushTerminate();
+      else
+        CGM.getDiags().Report(D->getLocation(),
+                              diag::warn_wasm_dynamic_exception_spec_ignored)
+            << FD->getExceptionSpecSourceRange();
+      return;
+    }
     unsigned NumExceptions = Proto->getNumExceptions();
     EHFilterScope *Filter = EHStack.pushFilter(NumExceptions);
 
@@ -544,6 +557,14 @@ void CodeGenFunction::EmitEndEHSpec(const Decl *D) {
     // 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
+    // case of throw with types, we ignore it and print a warning for now.
+    // TODO Correctly handle exception specification in wasm
+    if (getTarget().getCXXABI() == TargetCXXABI::WebAssembly) {
+      if (EST == EST_DynamicNone)
+        EHStack.popTerminate();
+      return;
+    }
     EHFilterScope &filterScope = cast<EHFilterScope>(*EHStack.begin());
     emitFilterDispatchBlock(*this, filterScope);
     EHStack.popFilter();