PR c++/54955 - Fail to parse alignas expr at the beginning of a declaration

In this PR, g++ embarrassingly fails to parse the simple alignas
expression below:

    alignas(double) int f;

even though the simple-declaration production in Clause 7 suggests
otherwise.

Fixed thus and tested on x86_64-unknown-linux-gnu against trunk.

gcc/cp

	PR c++/54955
	* parser.c (cp_nth_tokens_can_be_std_attribute_p): Recognize the
	'Alignas' keyword as the beginning of a c++11 attribute specifier.
	Update the comment of the function.
	(cp_next_tokens_can_be_gnu_attribute_p): Update the comment of the
	function.

gcc/testsuite/

	PR c++/54955
	* g++.dg/cpp0x/gen-attrs-48-2.C: New test.

From-SVN: r193029

gcc/cp/ChangeLog

+2012-10-31  Dodji Seketeli  <dodji@redhat.com>
+
+	PR c++/54955
+	* parser.c (cp_nth_tokens_can_be_std_attribute_p): Recognize the
+	'Alignas' keyword as the beginning of a c++11 attribute specifier.
+	Update the comment of the function.
+	(cp_next_tokens_can_be_gnu_attribute_p): Update the comment of the
+	function.
+
 2012-10-29  Jonathan Wakely  <jwakely.gcc@gmail.com>
 
 	PR c++/54930

gcc/cp/parser.c

@@ -20324,7 +20324,7 @@ cp_next_tokens_can_be_gnu_attribute_p (cp_parser *parser)
 }
 
 /* Return TRUE iff the next tokens in the stream are possibly the
-   beginning of a standard C++-11 attribute.  */
+   beginning of a standard C++-11 attribute specifier.  */
 
 static bool
 cp_next_tokens_can_be_std_attribute_p (cp_parser *parser)
@@ -20333,7 +20333,7 @@ cp_next_tokens_can_be_std_attribute_p (cp_parser *parser)
 }
 
 /* Return TRUE iff the next Nth tokens in the stream are possibly the
-   beginning of a standard C++-11 attribute.  */
+   beginning of a standard C++-11 attribute specifier.  */
 
 static bool
 cp_nth_tokens_can_be_std_attribute_p (cp_parser *parser, size_t n)
@@ -20341,9 +20341,10 @@ cp_nth_tokens_can_be_std_attribute_p (cp_parser *parser, size_t n)
   cp_token *token = cp_lexer_peek_nth_token (parser->lexer, n);
 
   return (cxx_dialect >= cxx0x
-	  && token->type == CPP_OPEN_SQUARE
+	  && ((token->type == CPP_KEYWORD && token->keyword == RID_ALIGNAS)
+	      || (token->type == CPP_OPEN_SQUARE
 		  && (token = cp_lexer_peek_nth_token (parser->lexer, n + 1))
-	  && token->type == CPP_OPEN_SQUARE);
+		  && token->type == CPP_OPEN_SQUARE)));
 }
 
 /* Return TRUE iff the next Nth tokens in the stream are possibly the

gcc/testsuite/ChangeLog

+2012-10-31  Dodji Seketeli  <dodji@redhat.com>
+
+	PR c++/54955
+	* g++.dg/cpp0x/gen-attrs-48-2.C: New test.
+
 2012-10-31  Jakub Jelinek  <jakub@redhat.com>
 
 	PR tree-optimization/19105

gcc/testsuite/g++.dg/cpp0x/gen-attrs-48-2.C

+// Origin: PR c++/54955
+// { dg-do compile { target c++11 } }
+
+alignas(double) int f;