StringOptimization: fix a crash when constant folding the type name of an inner class

rdar://problem/66540633

lib/SILOptimizer/Transforms/StringOptimization.cpp

@@ -257,12 +257,16 @@ static bool containsProblematicNode(Demangle::Node *node, bool qualified) {
       if (qualified)
         return true;
       break;
-    case Demangle::Node::Kind::Class:
+    case Demangle::Node::Kind::Class: {
       // ObjC class names are not derived from the mangling but from the
       // ObjC runtime. We cannot constant fold this.
-      if (node->getChild(0)->getText() == "__C")
+      Demangle::Node *context = node->getChild(0);
+      if (context->getKind() == Demangle::Node::Kind::Module &&
+          context->getText() == "__C") {
         return true;
+      }
       break;
+    }
     default:
       break;
   }

test/SILOptimizer/string_optimization.swift

@@ -13,6 +13,8 @@ import Foundation
 struct Outer {
   struct Inner { }
 
+  class InnerClass { }
+
   static let staticString = "static"
 }
 
@@ -94,6 +96,15 @@ public func testQualifiedLocalType() -> String {
   return _typeName(LocalStruct.self, qualified: true)
 }
 
+// CHECK-LABEL: sil [noinline] @$s4test0A10InnerClassSSyF
+// CHECK-NOT: apply
+// CHECK-NOT: bb1
+// CHECK: } // end sil function '$s4test0A10InnerClassSSyF'
+@inline(never)
+public func testInnerClass() -> String {
+  return _typeName(Outer.InnerClass.self, qualified: true)
+}
+
 #if _runtime(_ObjC)
 @inline(never)
 public func testObjcClassName(qualified: Bool) -> String {
@@ -101,6 +112,7 @@ public func testObjcClassName(qualified: Bool) -> String {
 }
 #endif
 
+
 @inline(never)
 func printEmbeeded(_ s: String) {
   print("<\(s)>")
@@ -130,6 +142,9 @@ printEmbeeded(testUnqualifiedLocalType())
 // CHECK-OUTPUT: <test.(unknown context at {{.*}}).LocalStruct>
 printEmbeeded(testQualifiedLocalType())
 
+// CHECK-OUTPUT: <test.Outer.InnerClass>
+printEmbeeded(testInnerClass())
+
 #if _runtime(_ObjC)
 
 // Can't use check-output here, because for non ObjC runtimes it would not match.