Add string-to-int bitcast test

Author: tbaederr

clang/test/AST/Interp/builtin-bit-cast.cpp

@@ -31,9 +31,24 @@ template <class To, class From>
 constexpr To bit_cast(const From &from) {
   static_assert(sizeof(To) == sizeof(From));
   return __builtin_bit_cast(To, from); // ref-note 2{{indeterminate value can only initialize}} \
-                                       // expected-note 2{{indeterminate value can only initialize}}
+                                       // expected-note 2{{indeterminate value can only initialize}} \
+                                       // ref-note {{subexpression not valid}}
 }
 
+
+/// Current interpreter does not support this.
+/// https://github.com/llvm/llvm-project/issues/63686
+constexpr int FromString = bit_cast<int>("abc"); // ref-error {{must be initialized by a constant expression}} \
+                                                 // ref-note {{in call to}} \
+                                                 // ref-note {{declared here}}
+#if LITTLE_END
+static_assert(FromString == 6513249); // ref-error {{is not an integral constant expression}} \
+                                      // ref-note {{initializer of 'FromString' is not a constant expression}}
+#else
+static_assert(FromString == 1633837824); // ref-error {{is not an integral constant expression}} \
+                                         // ref-note {{initializer of 'FromString' is not a constant expression}}
+#endif
+
 template <class Intermediate, class Init>
 constexpr bool round_trip(const Init &init) {
   return bit_cast<Init>(bit_cast<Intermediate>(init)) == init;