Add a long double -> int128 test

Author: tbaederr

clang/lib/AST/ByteCode/Opcodes.td

@@ -837,8 +837,12 @@ def CheckNewTypeMismatchArray : Opcode {
 
 def IsConstantContext: Opcode;
 
+def BitCastTypeClass : TypeClass {
+  let Types = [Uint8, Sint8, Uint16, Sint16, Uint32, Sint32, Uint64, Sint64, IntAP, IntAPS, Bool, Float];
+}
+
 def BitCast : Opcode {
-  let Types = [FixedSizeIntegralTypeClass];
+  let Types = [BitCastTypeClass];
   let Args = [ArgBool, ArgUint32, ArgFltSemantics];
   let HasGroup = 1;
 }

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

@@ -122,6 +122,13 @@ namespace bitint {
                                 // ref-note {{initializer of 'IB' is not a constant expression}}
 }
 
+/// FIXME: This is correct in the current interpreter.
+namespace LongDouble {
+  constexpr long double F = 12.0;
+  constexpr __int128 I = __builtin_bit_cast(__int128, F); // ref-error {{must be initialized by a constant expression}} \
+                                                          // ref-note {{indeterminate value can only initialize an object of type}}
+}
+
 namespace BitFields {
   struct BitFields {
     unsigned a : 2;