c: C2x storage class specifiers in compound literals

Implement the C2x feature of storage class specifiers in compound
literals.  Such storage class specifiers (static, register or
thread_local; also constexpr, but we don't yet have C2x constexpr
support implemented) can be used before the type name (not mixed with
type specifiers, unlike in declarations) and have the same semantics
and constraints as for declarations of named objects.  Also allow GNU
__thread to be used, given that thread_local can be.

Bootstrapped with no regressions for x86_64-pc-linux-gnu.

gcc/c/
	* c-decl.cc (build_compound_literal): Add parameter scspecs.
	Handle storage class specifiers.
	* c-parser.cc (c_token_starts_compound_literal)
	(c_parser_compound_literal_scspecs): New.
	(c_parser_postfix_expression_after_paren_type): Add parameter
	scspecs.  Call pedwarn_c11 for use of storage class specifiers.
	Update call to build_compound_literal.
	(c_parser_cast_expression, c_parser_sizeof_expression)
	(c_parser_alignof_expression): Handle storage class specifiers for
	compound literals.  Update calls to
	c_parser_postfix_expression_after_paren_type.
	(c_parser_postfix_expression): Update syntax comment.
	* c-tree.h (build_compound_literal): Update prototype.
	* c-typeck.cc (c_mark_addressable): Diagnose taking address of
	register compound literal.

gcc/testsuite/
	* gcc.dg/c11-complit-1.c, gcc.dg/c11-complit-2.c,
	gcc.dg/c11-complit-3.c, gcc.dg/c2x-complit-2.c,
	gcc.dg/c2x-complit-3.c, gcc.dg/c2x-complit-4.c,
	gcc.dg/c2x-complit-5.c, gcc.dg/c2x-complit-6.c,
	gcc.dg/c2x-complit-7.c, gcc.dg/c90-complit-2.c,
	gcc.dg/gnu2x-complit-1.c, gcc.dg/gnu2x-complit-2.c: New tests.

1 files changed, 30 insertions, 3 deletions

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index 193e268..a7571cc 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -6048,11 +6048,13 @@ mark_forward_parm_decls (void)
    literal.  NON_CONST is true if the initializers contain something
    that cannot occur in a constant expression.  If ALIGNAS_ALIGN is nonzero,
    it is the (valid) alignment for this compound literal, as specified
-   with _Alignas.  */
+   with _Alignas.  SCSPECS are the storage class specifiers (C2x) from the
+   compound literal.  */
 
 tree
 build_compound_literal (location_t loc, tree type, tree init, bool non_const,
-			unsigned int alignas_align)
+			unsigned int alignas_align,
+			struct c_declspecs *scspecs)
 {
   /* We do not use start_decl here because we have a type, not a declarator;
      and do not use finish_decl because the decl should be stored inside
@@ -6060,15 +6062,33 @@ build_compound_literal (location_t loc, tree type, tree init, bool non_const,
   tree decl;
   tree complit;
   tree stmt;
+  bool threadp = scspecs ? scspecs->thread_p : false;
+  enum c_storage_class storage_class = (scspecs
+					? scspecs->storage_class
+					: csc_none);
 
   if (type == error_mark_node
       || init == error_mark_node)
     return error_mark_node;
 
+  if (current_scope == file_scope && storage_class == csc_register)
+    {
+      error_at (loc, "file-scope compound literal specifies %<register%>");
+      storage_class = csc_none;
+    }
+
+  if (current_scope != file_scope && threadp && storage_class == csc_none)
+    {
+      error_at (loc, "compound literal implicitly auto and declared %qs",
+		scspecs->thread_gnu_p ? "__thread" : "_Thread_local");
+      threadp = false;
+    }
+
   decl = build_decl (loc, VAR_DECL, NULL_TREE, type);
   DECL_EXTERNAL (decl) = 0;
   TREE_PUBLIC (decl) = 0;
-  TREE_STATIC (decl) = (current_scope == file_scope);
+  TREE_STATIC (decl) = (current_scope == file_scope
+			|| storage_class == csc_static);
   DECL_CONTEXT (decl) = current_function_decl;
   TREE_USED (decl) = 1;
   DECL_READ_P (decl) = 1;
@@ -6076,6 +6096,13 @@ build_compound_literal (location_t loc, tree type, tree init, bool non_const,
   DECL_IGNORED_P (decl) = 1;
   C_DECL_COMPOUND_LITERAL_P (decl) = 1;
   TREE_TYPE (decl) = type;
+  if (threadp)
+    set_decl_tls_model (decl, decl_default_tls_model (decl));
+  if (storage_class == csc_register)
+    {
+      C_DECL_REGISTER (decl) = 1;
+      DECL_REGISTER (decl) = 1;
+    }
   c_apply_type_quals_to_decl (TYPE_QUALS (strip_array_types (type)), decl);
   if (alignas_align)
     {