[WebAssembly] Hide new Wasm EH behind its feature flag

[aheejin]

Summary

clang's current wasm EH implementation is a non-MVP feature in progress.
We had a -mexception-handling wasm feature but were not using it. This
patch hides the non-MVP wasm EH behind a flag, so it does not affect
other code for now.

[aheejin]

• Add a missing conditional statement. I'll still assume this as accepted

[sbc100]

lib/CodeGen/CGException.cpp

322

If the triple can be derived from target why not just pass that target?

[aheejin]

lib/CodeGen/CGException.cpp

322

Done in D47620. Thanks!

lib/CodeGen/CGException.cpp

case ObjCRuntime::ObjFW:
     if (L.SEHExceptions)
       return EHPersonality::GNU_ObjC_SEH;
     return EHPersonality::GNU_ObjC;
   }
   llvm_unreachable("bad runtime kind");
 }
 
 static const EHPersonality &getCXXPersonality(const llvm::Triple &T,
-                                              const LangOptions &L) {
+                                              const LangOptions &L,
+                                              const TargetInfo &Target) {
   if (L.SjLjExceptions)
     return EHPersonality::GNU_CPlusPlus_SJLJ;
   if (L.DWARFExceptions)
     return EHPersonality::GNU_CPlusPlus;
   if (T.isWindowsMSVCEnvironment())
     return EHPersonality::MSVC_CxxFrameHandler3;
   if (L.SEHExceptions)
     return EHPersonality::GNU_CPlusPlus_SEH;
-  if (T.getArch() == llvm::Triple::wasm32 ||
-      T.getArch() == llvm::Triple::wasm64)
+  // Wasm EH is a non-MVP feature for now.
+  if (Target.hasFeature("exception-handling") &&
+      (T.getArch() == llvm::Triple::wasm32 ||
+       T.getArch() == llvm::Triple::wasm64))
     return EHPersonality::GNU_Wasm_CPlusPlus;
   return EHPersonality::GNU_CPlusPlus;
 }
 
 /// Determines the personality function to use when both C++
 /// and Objective-C exceptions are being caught.
 static const EHPersonality &getObjCXXPersonality(const llvm::Triple &T,
-                                                 const LangOptions &L) {
+                                                 const LangOptions &L,
+                                                 const TargetInfo &Target) {
   switch (L.ObjCRuntime.getKind()) {
   // In the fragile ABI, just use C++ exception handling and hope
   // they're not doing crazy exception mixing.
   case ObjCRuntime::FragileMacOSX:
-    return getCXXPersonality(T, L);
+    return getCXXPersonality(T, L, Target);
 
   // The ObjC personality defers to the C++ personality for non-ObjC
   // handlers.  Unlike the C++ case, we use the same personality
   // function on targets using (backend-driven) SJLJ EH.
   case ObjCRuntime::MacOSX:
   case ObjCRuntime::iOS:
   case ObjCRuntime::WatchOS:
     return getObjCPersonality(T, L);
if (T.getArch() == llvm::Triple::x86)
     return EHPersonality::MSVC_except_handler;
   return EHPersonality::MSVC_C_specific_handler;
 }
 
 const EHPersonality &EHPersonality::get(CodeGenModule &CGM,
                                         const FunctionDecl *FD) {
   const llvm::Triple &T = CGM.getTarget().getTriple();
   const LangOptions &L = CGM.getLangOpts();
+  const TargetInfo &Target = CGM.getTarget();
 
   // Functions using SEH get an SEH personality.
   if (FD && FD->usesSEHTry())
     return getSEHPersonalityMSVC(T);
 
   if (L.ObjC1)
-    return L.CPlusPlus ? getObjCXXPersonality(T, L) : getObjCPersonality(T, L);
-  return L.CPlusPlus ? getCXXPersonality(T, L) : getCPersonality(T, L);
+    return L.CPlusPlus ? getObjCXXPersonality(T, L, Target)
+                       : getObjCPersonality(T, L);
+  return L.CPlusPlus ? getCXXPersonality(T, L, Target) : getCPersonality(T, L);
 }
 
 const EHPersonality &EHPersonality::get(CodeGenFunction &CGF) {
   const auto *FD = CGF.CurCodeDecl;
   // For outlined finallys and filters, use the SEH personality in case they
   // contain more SEH. This mostly only affects finallys. Filters could
   // hypothetically use gnu statement expressions to sneak in nested SEH.
   FD = FD ? FD : CGF.CurSEHParent;
void CodeGenModule::SimplifyPersonality() {
 
   // Both the problem this endeavors to fix and the way the logic
   // above works is specific to the NeXT runtime.
   if (!LangOpts.ObjCRuntime.isNeXTFamily())
     return;
 
   const EHPersonality &ObjCXX = EHPersonality::get(*this, /*FD=*/nullptr);
   const EHPersonality &CXX =
-      getCXXPersonality(getTarget().getTriple(), LangOpts);
+      getCXXPersonality(getTarget().getTriple(), LangOpts, getTarget());
   if (&ObjCXX == &CXX)
     return;
 
   assert(std::strcmp(ObjCXX.PersonalityFn, CXX.PersonalityFn) != 0 &&
          "Different EHPersonalities using the same personality function.");
 
   llvm::Function *Fn = getModule().getFunction(ObjCXX.PersonalityFn);
 

lib/CodeGen/ItaniumCXXABI.cpp

 std::pair<llvm::Value *, const CXXRecordDecl *>
 ItaniumCXXABI::LoadVTablePtr(CodeGenFunction &CGF, Address This,
                              const CXXRecordDecl *RD) {
   return {CGF.GetVTablePtr(This, CGM.Int8PtrTy, RD), RD};
 }
 
 void WebAssemblyCXXABI::emitBeginCatch(CodeGenFunction &CGF,
                                        const CXXCatchStmt *C) {
+  if (CGF.getTarget().hasFeature("exception-handling"))
     CGF.EHStack.pushCleanup<CatchRetScope>(
         NormalCleanup, cast<llvm::CatchPadInst>(CGF.CurrentFuncletPad));
   ItaniumCXXABI::emitBeginCatch(CGF, C);
 }

test/CodeGenCXX/wasm-eh.cpp

-// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 | FileCheck %s
-// RUN: %clang_cc1 %s -triple wasm64-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 | FileCheck %s
+// RUN: %clang_cc1 %s -triple wasm32-unknown-unknown -fms-extensions -fexceptions -fcxx-exceptions -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 -target-feature +exception-handling -emit-llvm -o - -std=c++11 | FileCheck %s
 
 void may_throw();
 void dont_throw() noexcept;
 
 struct Cleanup {
   ~Cleanup() { dont_throw(); }
 };