Introduce IR bit TYPE_INCLUDES_FLEXARRAY for the GCC extension

on a structure with a C99 flexible array member being nested in
another structure

GCC extension accepts the case when a struct with a flexible array member
is embedded into another struct or union (possibly recursively) as the last
field.
This patch is to introduce the IR bit TYPE_INCLUDES_FLEXARRAY (reuse the
existing IR bit TYPE_NO_NAMED_ARGS_SATDARG_P), set it correctly in C FE,
stream it correctly in Middle-end, and print it during IR dumping.

gcc/c/ChangeLog:

	* c-decl.cc (finish_struct): Set TYPE_INCLUDES_FLEXARRAY for
	struct/union type.

gcc/lto/ChangeLog:

	* lto-common.cc (compare_tree_sccs_1): Compare bit
	TYPE_NO_NAMED_ARGS_STDARG_P or TYPE_INCLUDES_FLEXARRAY properly
	for its corresponding type.

gcc/ChangeLog:

	* print-tree.cc (print_node): Print new bit type_include_flexarray.
	* tree-core.h (struct tree_type_common): Use bit no_named_args_stdarg_p
	as type_include_flexarray for RECORD_TYPE or UNION_TYPE.
	* tree-streamer-in.cc (unpack_ts_type_common_value_fields): Stream
	in bit no_named_args_stdarg_p properly for its corresponding type.
	* tree-streamer-out.cc (pack_ts_type_common_value_fields): Stream
	out bit no_named_args_stdarg_p properly for its corresponding type.
	* tree.h (TYPE_INCLUDES_FLEXARRAY): New macro TYPE_INCLUDES_FLEXARRAY.

gcc/c/c-decl.cc

@@ -9267,6 +9267,17 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
       /* Set DECL_NOT_FLEXARRAY flag for FIELD_DECL x.  */
       DECL_NOT_FLEXARRAY (x) = !is_flexible_array_member_p (is_last_field, x);
 
+      /* Set TYPE_INCLUDES_FLEXARRAY for the context of x, t.
+	 when x is an array and is the last field.  */
+      if (TREE_CODE (TREE_TYPE (x)) == ARRAY_TYPE)
+	TYPE_INCLUDES_FLEXARRAY (t)
+	  = is_last_field && flexible_array_member_type_p (TREE_TYPE (x));
+      /* Recursively set TYPE_INCLUDES_FLEXARRAY for the context of x, t
+	 when x is an union or record and is the last field.  */
+      else if (RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
+	TYPE_INCLUDES_FLEXARRAY (t)
+	  = is_last_field && TYPE_INCLUDES_FLEXARRAY (TREE_TYPE (x));
+
       if (DECL_NAME (x)
 	  || RECORD_OR_UNION_TYPE_P (TREE_TYPE (x)))
 	saw_named_field = true;

gcc/lto/lto-common.cc

@@ -1275,7 +1275,10 @@ compare_tree_sccs_1 (tree t1, tree t2, tree **map)
       if (AGGREGATE_TYPE_P (t1))
 	compare_values (TYPE_TYPELESS_STORAGE);
       compare_values (TYPE_EMPTY_P);
-      compare_values (TYPE_NO_NAMED_ARGS_STDARG_P);
+      if (FUNC_OR_METHOD_TYPE_P (t1))
+	compare_values (TYPE_NO_NAMED_ARGS_STDARG_P);
+      if (RECORD_OR_UNION_TYPE_P (t1))
+	compare_values (TYPE_INCLUDES_FLEXARRAY);
       compare_values (TYPE_PACKED);
       compare_values (TYPE_RESTRICT);
       compare_values (TYPE_USER_ALIGN);

gcc/print-tree.cc

@@ -632,6 +632,11 @@ print_node (FILE *file, const char *prefix, tree node, int indent,
 	  && TYPE_CXX_ODR_P (node))
 	fputs (" cxx-odr-p", file);
 
+      if ((code == RECORD_TYPE
+	   || code == UNION_TYPE)
+	  && TYPE_INCLUDES_FLEXARRAY (node))
+	fputs (" includes-flexarray", file);
+
       /* The transparent-union flag is used for different things in
 	 different nodes.  */
       if ((code == UNION_TYPE || code == RECORD_TYPE)

gcc/tree-core.h

@@ -1713,6 +1713,8 @@ struct GTY(()) tree_type_common {
   unsigned typeless_storage : 1;
   unsigned empty_flag : 1;
   unsigned indivisible_p : 1;
+  /* TYPE_NO_NAMED_ARGS_STDARG_P for a stdarg function.
+     Or TYPE_INCLUDES_FLEXARRAY for RECORD_TYPE and UNION_TYPE.  */
   unsigned no_named_args_stdarg_p : 1;
   unsigned spare : 1;
 

gcc/tree-streamer-in.cc

@@ -386,7 +386,10 @@ unpack_ts_type_common_value_fields (struct bitpack_d *bp, tree expr)
   if (AGGREGATE_TYPE_P (expr))
     TYPE_TYPELESS_STORAGE (expr) = (unsigned) bp_unpack_value (bp, 1);
   TYPE_EMPTY_P (expr) = (unsigned) bp_unpack_value (bp, 1);
-  TYPE_NO_NAMED_ARGS_STDARG_P (expr) = (unsigned) bp_unpack_value (bp, 1);
+  if (FUNC_OR_METHOD_TYPE_P (expr))
+    TYPE_NO_NAMED_ARGS_STDARG_P (expr) = (unsigned) bp_unpack_value (bp, 1);
+  if (RECORD_OR_UNION_TYPE_P (expr))
+    TYPE_INCLUDES_FLEXARRAY (expr) = (unsigned) bp_unpack_value (bp, 1);
   TYPE_PRECISION_RAW (expr) = bp_unpack_var_len_unsigned (bp);
   SET_TYPE_ALIGN (expr, bp_unpack_var_len_unsigned (bp));
 #ifdef ACCEL_COMPILER

gcc/tree-streamer-out.cc

@@ -355,7 +355,10 @@ pack_ts_type_common_value_fields (struct bitpack_d *bp, tree expr)
   if (AGGREGATE_TYPE_P (expr))
     bp_pack_value (bp, TYPE_TYPELESS_STORAGE (expr), 1);
   bp_pack_value (bp, TYPE_EMPTY_P (expr), 1);
-  bp_pack_value (bp, TYPE_NO_NAMED_ARGS_STDARG_P (expr), 1);
+  if (FUNC_OR_METHOD_TYPE_P (expr))
+    bp_pack_value (bp, TYPE_NO_NAMED_ARGS_STDARG_P (expr), 1);
+  if (RECORD_OR_UNION_TYPE_P (expr))
+    bp_pack_value (bp, TYPE_INCLUDES_FLEXARRAY (expr), 1);
   bp_pack_var_len_unsigned (bp, TYPE_PRECISION_RAW (expr));
   bp_pack_var_len_unsigned (bp, TYPE_ALIGN (expr));
 }

gcc/tree.h

@@ -807,7 +807,12 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
    (...) prototype, where arguments can be accessed with va_start and
    va_arg), as opposed to an unprototyped function.  */
 #define TYPE_NO_NAMED_ARGS_STDARG_P(NODE) \
-  (TYPE_CHECK (NODE)->type_common.no_named_args_stdarg_p)
+  (FUNC_OR_METHOD_CHECK (NODE)->type_common.no_named_args_stdarg_p)
+
+/* True if this RECORD_TYPE or UNION_TYPE includes a flexible array member
+   as the last field recursively.  */
+#define TYPE_INCLUDES_FLEXARRAY(NODE) \
+  (RECORD_OR_UNION_CHECK (NODE)->type_common.no_named_args_stdarg_p)
 
 /* In an IDENTIFIER_NODE, this means that assemble_name was called with
    this string as an argument.  */