Fix assertion when try is used inside catch(...) block

Current assert wiht /EHa:
A single unwind edge may only enter one EH pad
  invoke void @llvm.seh.try.begin()
          to label %invoke.cont1 unwind label %catch.dispatch2

Current IR:
%1 = catchpad within %0 [ptr null, i32 0, ptr null]
   invoke void @llvm.seh.try.begin()
           to label %invoke.cont5 unwind label %catch.dispatch2

The problem is the invoke to llvm.seh.try.begin() missing "funclet"

Accodring: https://llvm.org/docs/LangRef.html#ob-funclet
If any "funclet" EH pads have been entered but not exited (per the
description in the EH doc), it is undefined behavior to execute a
call or invoke.

To fix the problem, when emit seh_try_begin,  call EmitSehTryScopeBegin,
instead of calling EmitRuntimeCallOrInvoke for proper "funclet"
gerenration.

Differential Revision: https://reviews.llvm.org/D150340

Author: jyu2-git

clang/lib/CodeGen/CGException.cpp

@@ -646,7 +646,7 @@ void CodeGenFunction::EnterCXXTryStmt(const CXXTryStmt &S, bool IsFnTryBlock) {
       // Under async exceptions, catch(...) need to catch HW exception too
       // Mark scope with SehTryBegin as a SEH __try scope
       if (getLangOpts().EHAsynch)
-        EmitRuntimeCallOrInvoke(getSehTryBeginFn(CGM));
+        EmitSehTryScopeBegin();
     }
   }
 }

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

@@ -9,11 +9,21 @@
 // CHECK: %[[dst1:[0-9-]+]] = catchpad within %[[dst]] [ptr null, i32 0, ptr null]
 // CHECK: "funclet"(token %[[dst1]])
 
+// CHECK: define dso_local void @"?bar@@YAXXZ
+// CHECK: invoke void @llvm.seh.try.begin()
+// CHECK: invoke void @_CxxThrowException
+// CHECK: %[[dst:[0-9-]+]] = catchpad within %0 [ptr null, i32 0, ptr null]
+// CHECK: invoke void @llvm.seh.try.begin() [ "funclet"(token %[[dst]]) ]
+
 // CHECK: invoke void @llvm.seh.try.begin()
 // CHECK: %[[src:[0-9-]+]] = load volatile i32, ptr %i
 // CHECK-NEXT: invoke void @"?crash@@YAXH@Z"(i32 noundef %[[src]])
 // CHECK: invoke void @llvm.seh.try.end()
 
+// CHECK: invoke void @llvm.seh.try.begin()
+// CHECK: invoke void @"?bar@@YAXXZ"()
+// CHECK: invoke void @llvm.seh.try.end()
+
 // *****************************************************************************
 // Abstract:     Test CPP catch(...) under SEH -EHa option
 
@@ -46,6 +56,18 @@ void crash(int i) {
   }
 }
 
+void bar() {
+  try {
+    throw 1;
+  } catch(...) {
+    try {
+      *NullPtr = 0;
+    } catch (...) {
+       throw 1;
+    }
+  }
+}
+
 int main() {
   for (int i = 0; i < 2; i++) {
     __try {
@@ -54,5 +76,10 @@ int main() {
       printf(" Test CPP unwind: in except handler i = %d \n", i);
     }
   }
+  __try {
+   bar();
+  } __except (1) {
+    printf("Test CPP unwind: in except handler \n");
+  }
   return 0;
 }