C _BitInt support [PR102989]

This patch adds the C FE support, c-family support, small libcpp change
so that 123wb and 42uwb suffixes are handled plus glimits.h change
to define BITINT_MAXWIDTH macro.

The previous patches really do nothing without this, which enables
all the support.

2023-09-06  Jakub Jelinek  <jakub@redhat.com>

	PR c/102989
gcc/
	* glimits.h (BITINT_MAXWIDTH): Define if __BITINT_MAXWIDTH__ is
	predefined.
gcc/c-family/
	* c-common.cc (c_common_reswords): Add _BitInt as keyword.
	(unsafe_conversion_p): Handle BITINT_TYPE like INTEGER_TYPE.
	(c_common_signed_or_unsigned_type): Handle BITINT_TYPE.
	(c_common_truthvalue_conversion, c_common_get_alias_set,
	check_builtin_function_arguments): Handle BITINT_TYPE like
	INTEGER_TYPE.
	(sync_resolve_size): Add ORIG_FORMAT argument.  If
	FETCH && !ORIG_FORMAT, type is BITINT_TYPE, return -1 if size isn't
	one of 1, 2, 4, 8 or 16 or if it is 16 but TImode is not supported.
	(atomic_bitint_fetch_using_cas_loop): New function.
	(resolve_overloaded_builtin): Adjust sync_resolve_size caller.  If
	-1 is returned, use atomic_bitint_fetch_using_cas_loop to lower it.
	Formatting fix.
	(keyword_begins_type_specifier): Handle RID_BITINT.
	* c-common.h (enum rid): Add RID_BITINT enumerator.
	* c-cppbuiltin.cc (c_cpp_builtins): For C call
	targetm.c.bitint_type_info and predefine __BITINT_MAXWIDTH__
	and for -fbuilding-libgcc also __LIBGCC_BITINT_LIMB_WIDTH__ and
	__LIBGCC_BITINT_ORDER__ macros if _BitInt is supported.
	* c-lex.cc (interpret_integer): Handle CPP_N_BITINT.
	* c-pretty-print.cc (c_pretty_printer::simple_type_specifier,
	c_pretty_printer::direct_abstract_declarator,
	c_pretty_printer::direct_declarator, c_pretty_printer::declarator):
	Handle BITINT_TYPE.
	(pp_c_integer_constant): Handle printing of large precision wide_ints
	which would buffer overflow digit_buffer.
	* c-warn.cc (conversion_warning, warnings_for_convert_and_check,
	warnings_for_convert_and_check): Handle BITINT_TYPE like
	INTEGER_TYPE.
gcc/c/
	* c-convert.cc (c_convert): Handle BITINT_TYPE like INTEGER_TYPE.
	* c-decl.cc (check_bitfield_type_and_width): Allow BITINT_TYPE
	bit-fields.
	(finish_struct): Prefer to use BITINT_TYPE for BITINT_TYPE bit-fields
	if possible.
	(declspecs_add_type): Formatting fixes.  Handle cts_bitint.  Adjust
	for added union in *specs.  Handle RID_BITINT.
	(finish_declspecs): Handle cts_bitint.  Adjust for added union
	in *specs.
	* c-parser.cc (c_keyword_starts_typename, c_token_starts_declspecs,
	c_parser_declspecs, c_parser_gnu_attribute_any_word): Handle
	RID_BITINT.
	(c_parser_omp_clause_schedule): Handle BITINT_TYPE like INTEGER_TYPE.
	* c-tree.h (enum c_typespec_keyword): Mention _BitInt in comment.
	Add cts_bitint enumerator.
	(struct c_declspecs): Move int_n_idx and floatn_nx_idx into a union
	and add bitint_prec there as well.
	* c-typeck.cc (c_common_type, comptypes_internal):
	Handle BITINT_TYPE.
	(perform_integral_promotions): Promote BITINT_TYPE bit-fields to
	their declared type.
	(build_array_ref, build_unary_op, build_conditional_expr,
	build_c_cast, convert_for_assignment, digest_init, build_binary_op):
	Handle BITINT_TYPE.
	* c-fold.cc (c_fully_fold_internal): Handle BITINT_TYPE like
	INTEGER_TYPE.
	* c-aux-info.cc (gen_type): Handle BITINT_TYPE.
libcpp/
	* expr.cc (interpret_int_suffix): Handle wb and WB suffixes.
	* include/cpplib.h (CPP_N_BITINT): Define.

libcpp/expr.cc

@@ -327,9 +327,9 @@ static unsigned int
 interpret_int_suffix (cpp_reader *pfile, const uchar *s, size_t len)
 {
   size_t orig_len = len;
-  size_t u, l, i, z;
+  size_t u, l, i, z, wb;
 
-  u = l = i = z = 0;
+  u = l = i = z = wb = 0;
 
   while (len--)
     switch (s[len])
@@ -343,11 +343,23 @@ interpret_int_suffix (cpp_reader *pfile, const uchar *s, size_t len)
 	if (l == 2 && s[len] != s[len + 1])
 	  return 0;
 	break;
+      case 'b':
+	if (len == 0 || s[len - 1] != 'w')
+	  return 0;
+	wb++;
+	len--;
+	break;
+      case 'B':
+	if (len == 0 || s[len - 1] != 'W')
+	  return 0;
+	wb++;
+	len--;
+	break;
       default:
 	return 0;
       }
 
-  if (l > 2 || u > 1 || i > 1 || z > 1)
+  if (l > 2 || u > 1 || i > 1 || z > 1 || wb > 1)
     return 0;
 
   if (z)
@@ -358,6 +370,14 @@ interpret_int_suffix (cpp_reader *pfile, const uchar *s, size_t len)
 	return 0;
     }
 
+  if (wb)
+    {
+      if (CPP_OPTION (pfile, cplusplus))
+	return 0;
+      if (l > 0 || i > 0 || z > 0)
+	return 0;
+    }
+
   if (i)
     {
       if (!CPP_OPTION (pfile, ext_numeric_literals))
@@ -376,7 +396,8 @@ interpret_int_suffix (cpp_reader *pfile, const uchar *s, size_t len)
 	  | (u ? CPP_N_UNSIGNED : 0)
 	  | ((l == 0) ? CPP_N_SMALL
 	     : (l == 1) ? CPP_N_MEDIUM : CPP_N_LARGE)
-	  | (z ? CPP_N_SIZE_T : 0));
+	  | (z ? CPP_N_SIZE_T : 0)
+	  | (wb ? CPP_N_BITINT : 0));
 }
 
 /* Return the classification flags for an int suffix.  */

libcpp/include/cpplib.h

@@ -1284,6 +1284,7 @@ struct cpp_num
 
 #define CPP_N_SIZE_T	0x2000000 /* C++23 size_t literal.  */
 #define CPP_N_BFLOAT16	0x4000000 /* std::bfloat16_t type.  */
+#define CPP_N_BITINT	0x8000000 /* C2X _BitInt literal.  */
 
 #define CPP_N_WIDTH_FLOATN_NX	0xF0000000 /* _FloatN / _FloatNx value
 					      of N, divided by 16.  */