PR middle-end/84108 - incorrect -Wattributes warning for packed/aligned conflict on struct members

gcc/ChangeLog:

	PR c/84108
	* attribs.c (diag_attr_exclusions): Consider the exclusion(s)
	that correspond to the kind of a declaration.

gcc/testsuite/ChangeLog:

	PR c/84108
	* gcc.dg/Wattributes-8.c: New test.

From-SVN: r257674

gcc/ChangeLog

+2018-02-14  Martin Sebor  <msebor@redhat.com>
+
+	PR c/84108
+	* attribs.c (diag_attr_exclusions): Consider the exclusion(s)
+	that correspond to the kind of a declaration.
+
 2018-02-14  John David Anglin  <danglin@gcc.gnu.org>
 
 	PR target/83984

gcc/attribs.c

@@ -410,6 +410,22 @@ diag_attr_exclusions (tree last_decl, tree node, tree attrname,
 	  if (!lookup_attribute (excl->name, attrs[i]))
 	    continue;
 
+	  /* An exclusion may apply either to a function declaration,
+	     type declaration, or a field/variable declaration, or
+	     any subset of the three.  */
+	  if (TREE_CODE (node) == FUNCTION_DECL
+	      && !excl->function)
+	    continue;
+
+	  if (TREE_CODE (node) == TYPE_DECL
+	      && !excl->type)
+	    continue;
+
+	  if ((TREE_CODE (node) == FIELD_DECL
+	       || TREE_CODE (node) == VAR_DECL)
+	      && !excl->variable)
+	    continue;
+
 	  found = true;
 
 	  /* Print a note?  */

gcc/testsuite/ChangeLog

+2018-02-14  Martin Sebor  <msebor@redhat.com>
+
+	PR c/84108
+	* gcc.dg/Wattributes-8.c: New test.
+
 2018-02-14  Janus Weil  <janus@gcc.gnu.org>
 
 	PR fortran/84385

gcc/testsuite/gcc.dg/Wattributes-8.c

+/* PR middle-end/84108 - incorrect -Wattributes warning for packed/aligned
+   conflict on struct members
+   { dg-do compile }
+   { dg-options "-Wall -Wattributes" } */
+
+#define ATTR(list) __attribute__ (list)
+#define ASSERT(e) _Static_assert (e, #e)
+
+/* GCC is inconsistent in how it treats attribute aligned between
+   variable and member declarations.  Attribute aligned alone is
+   sufficient to reduce a variable's alignment requirement but
+   the attribute must be paired with packed to have the same
+   effect on a member.  Worse, declaring a variable both aligned
+   and packed emits a warning.  */
+
+/* Avoid exercising this since emitting a warning for these given
+   the requirement for members seems like a misfeature:
+   int a ATTR ((packed, aligned (2)));   // -Wattributes
+   int b ATTR ((aligned (2), packed));   // -Wattributes
+   ASSERT (_Alignof (a) == 2);
+   ASSERT (_Alignof (b) == 2);  */
+
+int c ATTR ((aligned (2)));           // okay (reduces alignment)
+ASSERT (_Alignof (c) == 2);
+
+struct {
+  int a ATTR ((packed, aligned (2)));   /* { dg-bogus "\\\[-Wattributes" } */
+  int b ATTR ((aligned (2), packed));   /* { dg-bogus "\\\[-Wattributes" } */
+
+  /* Avoid exercising this since the attribute has no effect yet
+     there is no warning.
+     int c ATTR ((aligned (2)));           // missing warning?  */
+} s;
+
+ASSERT (_Alignof (s.a) == 2);
+ASSERT (_Alignof (s.b) == 2);
+
+/* ASSERT (_Alignof (s.c) == 4); */