[clang] Add bitint classification for __builtin_classify_type (#72036)

See #71911

Author: tbaederr

clang/docs/ReleaseNotes.rst

@@ -219,6 +219,8 @@ Non-comprehensive list of changes in this release
   determined at runtime.
 * The ``__datasizeof`` keyword has been added. It is similar to ``sizeof``
   except that it returns the size of a type ignoring tail padding.
+* ``__builtin_classify_type()`` now classifies ``_BitInt`` values as the return value ``18``,
+  to match GCC 14's behavior.
 
 New Compiler Flags
 ------------------

clang/lib/AST/ExprConstant.cpp

@@ -11520,6 +11520,9 @@ enum class GCCTypeClass {
   // decay to pointer. (Prior to version 6 it was only used in C++ mode).
   // GCC reserves 15 for strings, but actually uses 5 (pointer) for string
   // literals.
+  // Lang = 16,
+  // OpaqueType = 17,
+  BitInt = 18
 };
 
 /// EvaluateBuiltinClassifyType - Evaluate __builtin_classify_type the same way
@@ -11652,11 +11655,13 @@ EvaluateBuiltinClassifyType(QualType T, const LangOptions &LangOpts) {
   case Type::ObjCInterface:
   case Type::ObjCObjectPointer:
   case Type::Pipe:
-  case Type::BitInt:
     // GCC classifies vectors as None. We follow its lead and classify all
     // other types that don't fit into the regular classification the same way.
     return GCCTypeClass::None;
 
+  case Type::BitInt:
+    return GCCTypeClass::BitInt;
+
   case Type::LValueReference:
   case Type::RValueReference:
     llvm_unreachable("invalid type for expression");

clang/test/Sema/builtin-classify-type.c

@@ -11,7 +11,8 @@ enum gcc_type_class {
   function_type_class, method_type_class,
   record_type_class, union_type_class,
   array_type_class, string_type_class,
-  lang_type_class
+  lang_type_class, opaque_type_class,
+  bitint_type_class
 };
 
 void foo(void) {
@@ -45,6 +46,7 @@ void foo(void) {
   vint32_t3 vt5;
   typedef _BitInt(64) vint64_t3 __attribute__((vector_size(16)));
   vint64_t3 vt6;
+  _BitInt(16) bitint;
 
   _Atomic int atomic_i;
   _Atomic double atomic_d;
@@ -70,6 +72,7 @@ void foo(void) {
   int a17[__builtin_classify_type(atomic_d) == real_type_class ? 1 : -1];
   int a18[__builtin_classify_type(complex_i) == complex_type_class ? 1 : -1];
   int a19[__builtin_classify_type(complex_d) == complex_type_class ? 1 : -1];
+  int a20[__builtin_classify_type(bitint) == bitint_type_class ? 1 : -1];
 }
 
 extern int (^p)(void);

clang/test/SemaCXX/builtin-classify-type.cpp

@@ -11,7 +11,8 @@ enum gcc_type_class {
   function_type_class, method_type_class,
   record_type_class, union_type_class,
   array_type_class, string_type_class,
-  lang_type_class
+  lang_type_class, opaque_type_class,
+  bitint_type_class
 };
 
 class cl {
@@ -42,6 +43,7 @@ void foo() {
   _Atomic double atomic_d;
   _Complex int complex_i;
   _Complex double complex_d;
+  _BitInt(32) bitint;
 
   int a1[__builtin_classify_type(f()) == void_type_class ? 1 : -1];
   int a2[__builtin_classify_type(i) == integer_type_class ? 1 : -1];
@@ -65,5 +67,6 @@ void foo() {
   int a20[__builtin_classify_type(atomic_d) == real_type_class ? 1 : -1];
   int a21[__builtin_classify_type(complex_i) == complex_type_class ? 1 : -1];
   int a22[__builtin_classify_type(complex_d) == complex_type_class ? 1 : -1];
+  int a23[__builtin_classify_type(bitint) == bitint_type_class ? 1 : -1];
 }