add additional tests

Author: a-tarasyuk

clang/test/SemaCXX/constexpr-return-non-void-cxx2b.cpp

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -Wimplicit-fallthrough -verify %s
 
 constexpr int f() { } // expected-warning {{non-void function does not return a value}}
 static_assert(__is_same(decltype([] constexpr -> int { }( )), int)); // expected-warning {{non-void lambda does not return a value}}
@@ -10,4 +10,27 @@ namespace GH116485 {
 int h() {
     if consteval { }
 } // expected-warning {{non-void function does not return a value}}
+
+void i(int x) {
+  if consteval {
+  }
+  switch (x) {
+  case 1:
+    i(1);
+  case 2: // expected-warning {{unannotated fall-through between switch labels}} \
+          // expected-note {{insert 'break;' to avoid fall-through}}
+    break;
+  }
+}
+
+constexpr bool j()  {
+    if !consteval { return true; }
+} // expected-warning {{non-void function does not return a value in all control paths}} \
+  // expected-note {{control reached end of constexpr function}}
+
+bool k = j();
+constinit bool l = j(); // expected-error {{variable does not have a constant initializer}} \
+                        // expected-note {{required by 'constinit' specifier here}} \
+                        // expected-note {{in call to 'j()'}}
+
 }