[WebAssembly] Warn on exception spec only when Wasm EH is used

[aheejin]

Summary

In D80061 we added warning for exception specifications with types (such
as throw(int)), but it was enabled every time the target was wasm,
which means it warned (and ignored) exception specifications even if
wasm EH was not used. This fixes it and we only have the warning when we
enable -fwasm-exceptions.

[aheejin]

• Fix warning message

[dschuff]

otherwise LGTM

clang/docs/DiagnosticsReference.rst

14018 ↗

(On Diff #265432)

I think it's not actually necessary to change the text of the warning. Since the warning is about an exception handling language feature, I think adding "exception handling" on the end doesn't make it any more clear and sounds a little redundant to me.

[aheejin]

Address comments

clang/lib/CodeGen/CGException.cpp

void CodeGenFunction::EmitStartEHSpec(const Decl *D) {
   } else if (EST == EST_Dynamic || EST == EST_DynamicNone) {
     // TODO: Revisit exception specifications for the MS ABI.  There is a way to
     // 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 (CGM.getLangOpts().WasmExceptions) {
       if (EST == EST_DynamicNone)
         EHStack.pushTerminate();
       else
         CGM.getDiags().Report(D->getLocation(),
                               diag::warn_wasm_dynamic_exception_spec_ignored)
             << FD->getExceptionSpecSourceRange();
       return;
     }
void CodeGenFunction::EmitEndEHSpec(const Decl *D) {
   } else if (EST == EST_Dynamic || EST == EST_DynamicNone) {
     // TODO: Revisit exception specifications for the MS ABI.  There is a way to
     // 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 (CGM.getLangOpts().WasmExceptions) {
       if (EST == EST_DynamicNone)
         EHStack.popTerminate();
       return;
     }
     EHFilterScope &filterScope = cast<EHFilterScope>(*EHStack.begin());
     emitFilterDispatchBlock(*this, filterScope);
     EHStack.popFilter();
   }

clang/test/CodeGenCXX/wasm-eh.cpp

 // CHECK:   %[[CLEANUPPAD1:.*]] = cleanuppad within %[[CATCHPAD0]] []
 // CHECK:   cleanupret from %[[CLEANUPPAD1]] unwind to caller
 
 // CHECK:   unreachable
 
 // RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -fwasm-exceptions -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 -fwasm-exceptions -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 -fwasm-exceptions -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
 
-// Wasm ignores dynamic exception specifications with types at the moment. This
-// is controlled by -Wwasm-exception-spec, which is on by default. This warning
-// can be suppressed with -Wno-wasm-exception-spec.
-// Checks if a warning message is correctly printed or not printed depending on
-// the options.
+// Wasm EH ignores dynamic exception specifications with types at the moment.
+// This is controlled by -Wwasm-exception-spec, which is on by default. This
+// warning can be suppressed with -Wno-wasm-exception-spec. Checks if a warning
+// message is correctly printed or not printed depending on the options.
 void test9() throw(int) {
 }
 // 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
 
 // 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.
 void test10() throw() {
   throw 3;
 }
 // WARNING-DEFAULT: warning: 'test10' has a non-throwing exception specification but can still throw
 // WARNING-DEFAULT: function declared non-throwing here