[Windows SEH] Fix ehcleanup crash for Windows -EHa

[pengfei]

Summary

Builder.GetInsertBlock() may return null sometimes. https://godbolt.org/z/n1Ph47jP1

[efriedma]

LGTM

clang/test/CodeGen/windows-seh-EHa-CppCatchReturn.cpp

27

If a scope never ends because there's an "unreachable", that's fine, I think. The scope never dynamically ends (unless an exception is thrown). The backend deals with the same sort of thing for other constructs with a "begin" and "end". For example, a cleanuppad might not have a matching cleanupret.

[pengfei]

clang/test/CodeGen/windows-seh-EHa-CppCatchReturn.cpp

27

Thanks for the advice!

clang/lib/CodeGen/CGCleanup.cpp

if (Scope.isEHCleanup())
     cleanupFlags.setIsEHCleanupKind();
 
   // Under -EHa, invoke seh.scope.end() to mark scope end before dtor
   bool IsEHa = getLangOpts().EHAsynch && !Scope.isLifetimeMarker();
   const EHPersonality &Personality = EHPersonality::get(*this);
   if (!RequiresNormalCleanup) {
     // Mark CPP scope end for passed-by-value Arg temp
     //   per Windows ABI which is "normally" Cleanup in callee
-    if (IsEHa && getInvokeDest()) {
+    if (IsEHa && getInvokeDest() && Builder.GetInsertBlock()) {
       if (Personality.isMSVCXXPersonality())
         EmitSehCppScopeEnd();
     }
     destroyOptimisticNormalEntry(*this, Scope);
     EHStack.popCleanup();
   } else {
     // If we have a fallthrough and no other need for the cleanup,
     // emit it directly.
if (Personality.usesFuncletPads()) {
         ParentPad = llvm::ConstantTokenNone::get(CGM.getLLVMContext());
       CurrentFuncletPad = CPI = Builder.CreateCleanupPad(ParentPad);
     }
 
     // Non-MSVC personalities need to terminate when an EH cleanup throws.
     if (!Personality.isMSVCPersonality()) {
       EHStack.pushTerminate();
       PushedTerminate = true;
+    } else if (IsEHa && getInvokeDest()) {
+      EmitSehCppScopeEnd();
     }
 
     // We only actually emit the cleanup code if the cleanup is either
     // active or was used before it was deactivated.
     if (EHActiveFlag.isValid() || IsActive) {
       cleanupFlags.setIsForEHCleanup();
       EmitCleanup(*this, Fn, cleanupFlags, EHActiveFlag);
     }

clang/test/CodeGen/windows-seh-EHa-CppCatchReturn.cpp

 // RUN: %clang_cc1 -triple x86_64-windows -fasync-exceptions -fcxx-exceptions -fexceptions -fms-extensions -x c++ -Wno-implicit-function-declaration -S -emit-llvm %s -o - | FileCheck %s
 
 // CHECK: define dso_local void @"?foo@@YAXXZ
 // CHECK: invoke void @llvm.seh.try.begin()
 // CHECK-NOT: llvm.seh.scope.begin
 // CHECK-NOT: llvm.seh.scope.end
 
 // FIXME: Do we actually need llvm.seh.scope*?
 void foo() {
   try {}
   catch (...) {
   return;
   }
 }
+
+__declspec(noreturn) void bar();
+class baz {
+public:
+  ~baz();
+};
+
+// CHECK: define dso_local void @"?qux@@YAXXZ
+// CHECK: invoke void @llvm.seh.scope.begin()
+// CHECK-NOT: llvm.seh.try
+// CHECK-NOT: llvm.seh.scope.end
+
+// We don't need to generate llvm.seh.scope.end for unreachable.
+void qux() {
+  baz a;
+  bar();
+}