C: Detect all variably modified types [PR108375]

Some variably modified types were not detected correctly.
Define C_TYPE_VARIABLY_MODIFIED via TYPE_LANG_FLAG 6 in the CFE.
This flag records whether a type is variably modified and is
set for all such types including arrays with variably modified
element type or structures and unions with variably modified
members. This is then used to detect such types in the C FE
and middle-end (via the existing language hook).

gcc/c/ChangeLog:
	PR c/108375
	* c-decl.cc (decl_jump_unsafe): Use c_type_variably_modified_p.
	(diagnose_mismatched_decl): Dito.
	(warn_about_goto): Dito:
	(c_check_switch_jump_warnings): Dito.
	(finish_decl): Dito.
	(finish_struct): Dito.
	(grokdeclarator): Set C_TYPE_VARIABLY_MODIFIED.
	(finish_struct): Set C_TYPE_VARIABLY_MODIFIED.
	* c-objc-common.cc (c_var_mod_p): New function.
	(c_var_unspec_p): Remove.
	* c-objc-common.h: Set lang hook.
	* c-parser.cc (c_parser_declararion_or_fndef): Use c_type_variably_modified_p.
	(c_parser_typeof_specifier): Dito.
	(c_parser_has_attribute_expression): Dito.
	(c_parser_generic_selection): Dito.
	* c-tree.h: Define C_TYPE_VARIABLY_MODIFIED and define c_var_mode_p.
	* c-typeck.cc: Remove c_vla_mod_p and use C_TYPE_VARIABLY_MODIFIED.

gcc/testsuite/ChangeLog:
	PR c/108375
	* gcc.dg/pr108375-1.c: New test.
	* gcc.dg/pr108375-2.c: New test.

1 files changed, 21 insertions, 13 deletions

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 20e7d18..08078ea 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -683,7 +683,7 @@ decl_jump_unsafe (tree decl)
 
   /* Always warn about crossing variably modified types.  */
   if ((VAR_P (decl) || TREE_CODE (decl) == TYPE_DECL)
-      && variably_modified_type_p (TREE_TYPE (decl), NULL_TREE))
+      && c_type_variably_modified_p (TREE_TYPE (decl)))
     return true;
 
   /* Otherwise, only warn if -Wgoto-misses-init and this is an
@@ -2247,7 +2247,7 @@ diagnose_mismatched_decls (tree newdecl, tree olddecl,
 	  || warning_suppressed_p (olddecl, OPT_Wpedantic))
 	return true;  /* Allow OLDDECL to continue in use.  */
 
-      if (variably_modified_type_p (newtype, NULL))
+      if (c_type_variably_modified_p (newtype))
 	{
 	  error ("redefinition of typedef %q+D with variably modified type",
 		 newdecl);
@@ -3975,7 +3975,7 @@ static void
 warn_about_goto (location_t goto_loc, tree label, tree decl)
 {
   auto_diagnostic_group d;
-  if (variably_modified_type_p (TREE_TYPE (decl), NULL_TREE))
+  if (c_type_variably_modified_p (TREE_TYPE (decl)))
     error_at (goto_loc,
 	      "jump into scope of identifier with variably modified type");
   else
@@ -4249,7 +4249,7 @@ c_check_switch_jump_warnings (struct c_spot_bindings *switch_bindings,
 	    {
 	      auto_diagnostic_group d;
 	      bool emitted;
-	      if (variably_modified_type_p (TREE_TYPE (b->decl), NULL_TREE))
+	      if (c_type_variably_modified_p (TREE_TYPE (b->decl)))
 		{
 		  saw_error = true;
 		  error_at (case_loc,
@@ -5862,7 +5862,7 @@ finish_decl (tree decl, location_t init_loc, tree init,
   if (TREE_CODE (decl) == TYPE_DECL)
     {
       if (!DECL_FILE_SCOPE_P (decl)
-	  && variably_modified_type_p (TREE_TYPE (decl), NULL_TREE))
+	  && c_type_variably_modified_p (TREE_TYPE (decl)))
 	add_stmt (build_stmt (DECL_SOURCE_LOCATION (decl), DECL_EXPR, decl));
 
       rest_of_decl_compilation (decl, DECL_FILE_SCOPE_P (decl), 0);
@@ -6682,7 +6682,7 @@ grokdeclarator (const struct c_declarator *declarator,
 
   if ((decl_context == NORMAL || decl_context == FIELD)
       && current_scope == file_scope
-      && variably_modified_type_p (type, NULL_TREE))
+      && c_type_variably_modified_p (type))
     {
       if (name)
 	error_at (loc, "variably modified %qE at file scope", name);
@@ -6928,6 +6928,8 @@ grokdeclarator (const struct c_declarator *declarator,
 	  array_parm_static = false;
 	}
 
+      bool varmod = C_TYPE_VARIABLY_MODIFIED (type);
+
       switch (declarator->kind)
 	{
 	case cdk_attrs:
@@ -7282,8 +7284,7 @@ grokdeclarator (const struct c_declarator *declarator,
 		       variable size, so the enclosing shared array type
 		       must too.  */
 		    if (size && TREE_CODE (size) == INTEGER_CST)
-		      type
-			= build_distinct_type_copy (TYPE_MAIN_VARIANT (type));
+		      type = build_distinct_type_copy (TYPE_MAIN_VARIANT (type));
 		    C_TYPE_VARIABLE_SIZE (type) = 1;
 		  }
 
@@ -7493,7 +7494,7 @@ grokdeclarator (const struct c_declarator *declarator,
 	       the size evaluation prior to the side effects.  We therefore
 	       use BIND_EXPRs in TYPENAME contexts too.  */
 	    if (!TYPE_NAME (type)
-		&& variably_modified_type_p (type, NULL_TREE))
+		&& c_type_variably_modified_p (type))
 	      {
 		tree bind = NULL_TREE;
 		if (decl_context == TYPENAME || decl_context == PARM)
@@ -7534,6 +7535,8 @@ grokdeclarator (const struct c_declarator *declarator,
 	default:
 	  gcc_unreachable ();
 	}
+      if (type != error_mark_node)
+	C_TYPE_VARIABLY_MODIFIED (type) = varmod || size_varies;
     }
   *decl_attrs = chainon (returned_attrs, *decl_attrs);
   *decl_attrs = chainon (decl_id_attrs, *decl_attrs);
@@ -7728,7 +7731,7 @@ grokdeclarator (const struct c_declarator *declarator,
     }
 
   if (pedantic && decl_context == FIELD
-      && variably_modified_type_p (type, NULL_TREE))
+      && c_type_variably_modified_p (type))
     {
       /* C99 6.7.2.1p8 */
       pedwarn (loc, OPT_Wpedantic, "a member of a structure or union cannot "
@@ -7996,7 +7999,7 @@ grokdeclarator (const struct c_declarator *declarator,
 	       have a member with such a qualifier.  const
 	       qualification is implicitly added, and, at file scope,
 	       has internal linkage.  */
-	    if (variably_modified_type_p (type, NULL_TREE))
+	    if (c_type_variably_modified_p (type))
 	      error_at (loc, "%<constexpr%> object has variably modified "
 			"type");
 	    if (type_quals
@@ -8078,7 +8081,7 @@ grokdeclarator (const struct c_declarator *declarator,
 	 || (storage_class == csc_none
 	     && TREE_CODE (type) == FUNCTION_TYPE
 	     && !funcdef_flag))
-	&& variably_modified_type_p (type, NULL_TREE))
+	&& c_type_variably_modified_p (type))
       {
 	/* C99 6.7.5.2p2 */
 	if (TREE_CODE (type) == FUNCTION_TYPE)
@@ -9233,6 +9236,10 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
       if (C_DECL_VARIABLE_SIZE (x))
 	C_TYPE_VARIABLE_SIZE (t) = 1;
 
+      /* If any field is variably modified, record this fact. */
+      if (C_TYPE_VARIABLY_MODIFIED (TREE_TYPE (x)))
+	C_TYPE_VARIABLY_MODIFIED (t) = 1;
+
       if (DECL_C_BIT_FIELD (x))
 	{
 	  unsigned HOST_WIDE_INT width = tree_to_uhwi (DECL_INITIAL (x));
@@ -9431,6 +9438,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
       C_TYPE_FIELDS_VOLATILE (x) = C_TYPE_FIELDS_VOLATILE (t);
       C_TYPE_FIELDS_NON_CONSTEXPR (x) = C_TYPE_FIELDS_NON_CONSTEXPR (t);
       C_TYPE_VARIABLE_SIZE (x) = C_TYPE_VARIABLE_SIZE (t);
+      C_TYPE_VARIABLY_MODIFIED (x) = C_TYPE_VARIABLY_MODIFIED (t);
       C_TYPE_INCOMPLETE_VARS (x) = NULL_TREE;
     }
 
@@ -9447,7 +9455,7 @@ finish_struct (location_t loc, tree t, tree fieldlist, tree attributes,
   /* If we're inside a function proper, i.e. not file-scope and not still
      parsing parameters, then arrange for the size of a variable sized type
      to be bound now.  */
-  if (building_stmt_list_p () && variably_modified_type_p (t, NULL_TREE))
+  if (building_stmt_list_p () && c_type_variably_modified_p(t))
     add_stmt (build_stmt (loc,
 			  DECL_EXPR, build_decl (loc, TYPE_DECL, NULL, t)));