c: Allow duplicate C2x standard attributes

N2557, accepted into C2x at the October WG14 meeting, removes the
requirement that duplicates of standard attributes cannot appear
within an attribute list (so allowing e.g. [[deprecated, deprecated]],
where previously that was disallowed but [[deprecated]] [[deprecated]]
was OK).  Remove the code checking for this (standard attributes
aren't in any released version of the C standard) and update tests
accordingly.

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

gcc/c/
2020-10-27  Joseph Myers  <joseph@codesourcery.com>

	* c-parser.c (c_parser_std_attribute_specifier): Allow duplicate
	standard attributes.

gcc/testsuite/
2020-10-27  Joseph Myers  <joseph@codesourcery.com>

	* gcc.dg/c2x-attr-deprecated-4.c, gcc.dg/c2x-attr-fallthrough-4.c,
	gcc.dg/c2x-attr-maybe_unused-4.c: Allow duplicate attributes.

diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index b6a7ef4c92bdd33b7afb7271ba77a40519b45fb0..d49e508ce6d87a6dfebc2ea8ae0fde660329c93b 100644 (file)
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -4977,9 +4977,6 @@ c_parser_std_attribute (c_parser *parser, bool for_tm)
 static tree
 c_parser_std_attribute_specifier (c_parser *parser, bool for_tm)
 {
-  bool seen_deprecated = false;
-  bool seen_fallthrough = false;
-  bool seen_maybe_unused = false;
   location_t loc = c_parser_peek_token (parser)->location;
   if (!c_parser_require (parser, CPP_OPEN_SQUARE, "expected %<[%>"))
     return NULL_TREE;
@@ -5005,55 +5002,8 @@ c_parser_std_attribute_specifier (c_parser *parser, bool for_tm)
       tree attribute = c_parser_std_attribute (parser, for_tm);
       if (attribute != error_mark_node)
        {
-         bool duplicate = false;
-         tree name = get_attribute_name (attribute);
-         tree ns = get_attribute_namespace (attribute);
-         if (ns == NULL_TREE)
-           {
-             /* Some standard attributes may appear at most once in
-                each attribute list.  Diagnose duplicates and remove
-                them from the list to avoid subsequent diagnostics
-                such as the more general one for multiple
-                "fallthrough" attributes in the same place (including
-                in separate attribute lists in the same attribute
-                specifier sequence, which is not a constraint
-                violation).  */
-             if (is_attribute_p ("deprecated", name))
-               {
-                 if (seen_deprecated)
-                   {
-                     error ("attribute %<deprecated%> can appear at most "
-                            "once in an attribute-list");
-                     duplicate = true;
-                   }
-                 seen_deprecated = true;
-               }
-             else if (is_attribute_p ("fallthrough", name))
-               {
-                 if (seen_fallthrough)
-                   {
-                     error ("attribute %<fallthrough%> can appear at most "
-                            "once in an attribute-list");
-                     duplicate = true;
-                   }
-                 seen_fallthrough = true;
-               }
-             else if (is_attribute_p ("maybe_unused", name))
-               {
-                 if (seen_maybe_unused)
-                   {
-                     error ("attribute %<maybe_unused%> can appear at most "
-                            "once in an attribute-list");
-                     duplicate = true;
-                   }
-                 seen_maybe_unused = true;
-               }
-           }
-         if (!duplicate)
-           {
-             TREE_CHAIN (attribute) = attributes;
-             attributes = attribute;
-           }
+         TREE_CHAIN (attribute) = attributes;
+         attributes = attribute;
        }
       if (c_parser_next_token_is_not (parser, CPP_COMMA))
        break;

diff --git a/gcc/testsuite/gcc.dg/c2x-attr-deprecated-4.c b/gcc/testsuite/gcc.dg/c2x-attr-deprecated-4.c
index f1848a20cd54a72ea108e5e1874a9f3c2e123a9d..7698434cc6d9a2bf1c0b2048d8437b2504086f4a 100644 (file)
--- a/gcc/testsuite/gcc.dg/c2x-attr-deprecated-4.c
+++ b/gcc/testsuite/gcc.dg/c2x-attr-deprecated-4.c
@@ -1,13 +1,11 @@
-/* Test C2x deprecated attribute: duplicates.  */
+/* Test C2x deprecated attribute: duplicates (allowed after N2557).  */
 /* { dg-do compile } */
 /* { dg-options "-std=c2x -pedantic-errors" } */
 
-[[deprecated, __deprecated__]] int a; /* { dg-error "can appear at most once" } */
-[[__deprecated__, deprecated("message")]] int b; /* { dg-error "can appear at most once" } */
-int c [[deprecated("message"), deprecated]]; /* { dg-error "can appear at most once" } */
-[[deprecated, deprecated]]; /* { dg-error "can appear at most once" } */
+[[deprecated, __deprecated__]] int a;
+[[__deprecated__, deprecated("message")]] int b;
+int c [[deprecated("message"), deprecated]];
+[[deprecated, deprecated]];
 /* { dg-error "ignored" "ignored" { target *-*-* } .-1 } */
 
-/* Separate attribute lists in the same attribute specifier sequence,
-   with the same attribute in them, are OK.  */
 [[deprecated]] [[deprecated]] int d [[deprecated]] [[deprecated]];

diff --git a/gcc/testsuite/gcc.dg/c2x-attr-fallthrough-4.c b/gcc/testsuite/gcc.dg/c2x-attr-fallthrough-4.c
index 75aceff9941359c0ac80a78dbc44dd4cd3dee5df..a6cedcd0042bbaf6136ff470460e44a7e0e9285e 100644 (file)
--- a/gcc/testsuite/gcc.dg/c2x-attr-fallthrough-4.c
+++ b/gcc/testsuite/gcc.dg/c2x-attr-fallthrough-4.c
@@ -1,4 +1,4 @@
-/* Test C2x fallthrough attribute: duplicates.  */
+/* Test C2x fallthrough attribute: duplicates (allowed after N2557).  */
 /* { dg-do compile } */
 /* { dg-options "-std=c2x -pedantic-errors" } */
 
@@ -9,12 +9,9 @@ f (int a)
     {
     case 1:
       a++;
-      [[fallthrough, __fallthrough__]]; /* { dg-error "can appear at most once" } */
+      [[fallthrough, __fallthrough__]]; /* { dg-warning "specified multiple times" } */
     case 2:
       a++;
-      /* Separate attribute lists in the same attribute specifier
-        sequence, with the same attribute in them, are OK (but
-        receive a warning).  */
       [[fallthrough]] [[fallthrough]]; /* { dg-warning "specified multiple times" } */
     case 3:
       a++;

diff --git a/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-4.c b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-4.c
index 300c0dae73c16ef9674db80d715d1d240358ff64..6b997aa00334513a7fcc125f2e52f305b6910fae 100644 (file)
--- a/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-4.c
+++ b/gcc/testsuite/gcc.dg/c2x-attr-maybe_unused-4.c
@@ -1,13 +1,11 @@
-/* Test C2x maybe_unused attribute: duplicates.  */
+/* Test C2x maybe_unused attribute: duplicates (allowed after N2557).  */
 /* { dg-do compile } */
 /* { dg-options "-std=c2x -pedantic-errors" } */
 
-[[maybe_unused, __maybe_unused__]] int a; /* { dg-error "can appear at most once" } */
-[[__maybe_unused__, maybe_unused]] int b; /* { dg-error "can appear at most once" } */
-int c [[maybe_unused, maybe_unused]]; /* { dg-error "can appear at most once" } */
-[[maybe_unused, maybe_unused]]; /* { dg-error "can appear at most once" } */
+[[maybe_unused, __maybe_unused__]] int a;
+[[__maybe_unused__, maybe_unused]] int b;
+int c [[maybe_unused, maybe_unused]];
+[[maybe_unused, maybe_unused]];
 /* { dg-error "ignored" "ignored" { target *-*-* } .-1 } */
 
-/* Separate attribute lists in the same attribute specifier sequence,
-   with the same attribute in them, are OK.  */
 [[maybe_unused]] [[maybe_unused]] int d [[maybe_unused]] [[maybe_unused]];