[coroutines] Fix handling of dependent co_await in StmtProfiler

[vitaut]

Summary

Fix "Invalid operator call kind" error (llvm_unreachable) in
DecodeOperatorCall when compiling the following example with -emit-pch:

struct S {};
S operator co_await(S) { return S(); }

template <typename T>
int f3(T x) {
  co_await x;
}

Add the example to PCH test cases.

[rsmith]

Looks good, thanks. Do you need someone to commit this for you?

[vitaut]

Do you need someone to commit this for you?

Yes, please. I don't have commit rights.

lib/AST/StmtProfile.cpp

static Stmt::StmtClass DecodeOperatorCall(const CXXOperatorCallExpr *S,
   case OO_None:
   case OO_New:
   case OO_Delete:
   case OO_Array_New:
   case OO_Array_Delete:
   case OO_Arrow:
   case OO_Call:
   case OO_Conditional:
-  case OO_Coawait:
   case NUM_OVERLOADED_OPERATORS:
     llvm_unreachable("Invalid operator call kind");
       
   case OO_Plus:
     if (S->getNumArgs() == 1) {
       UnaryOp = UO_Plus;
       return Stmt::UnaryOperatorClass;
     }
case OO_Comma:
     return Stmt::BinaryOperatorClass;
 
   case OO_ArrowStar:
     BinaryOp = BO_PtrMemI;
     return Stmt::BinaryOperatorClass;
       
   case OO_Subscript:
     return Stmt::ArraySubscriptExprClass;
+
+  case OO_Coawait:
+    UnaryOp = UO_Coawait;
+    return Stmt::UnaryOperatorClass;
   }
   
   llvm_unreachable("Invalid overloaded operator expression");
 }
 
 #if defined(_MSC_VER) && !defined(__clang__)
 #if _MSC_VER == 1911
 // Work around https://developercommunity.visualstudio.com/content/problem/84002/clang-cl-when-built-with-vc-2017-crashes-cause-vc.html

test/PCH/coroutines.cpp

void f(T x) {  // checks coawait_expr and coroutine_body_stmt
   co_return;   // checks coreturn_stmt
 }
 
 template <typename T>
 int f2(T x) {  // checks coawait_expr and coroutine_body_stmt
   co_return x;   // checks coreturn_stmt with expr
 }
 
+struct S {};
+S operator co_await(S) { return S(); }
+
+template <typename T>
+int f3(T x) {
+  co_await x; // checks dependent_coawait with overloaded co_await operator
+}
+
 #else
 
 // expected-no-diagnostics
 void g() {
   f(suspend_always{});
   f2(42);
 }
 
 #endif