c++: Change the mangling of __alignof__ [PR88115]

This patch changes the mangling of __alignof__ to v111__alignof__,
making its mangling distinct from that of alignof(type) and
alignof(expr).

How we mangle ALIGNOF_EXPR now depends on its ALIGNOF_EXPR_STD_P flag,
which after the previous patch gets consistently set for alignof(type)
as well as alignof(expr).

gcc/c-family/ChangeLog:

	PR c++/88115
	* c-opts.c (c_common_post_options): Update latest_abi_version.

gcc/ChangeLog:

	PR c++/88115
	* common.opt (-fabi-version): Document =15.
	* doc/invoke.texi (C++ Dialect Options): Likewise.

gcc/cp/ChangeLog:

	PR c++/88115
	* mangle.c (write_expression): Mangle __alignof_ differently
	from alignof when the ABI version is at least 15.

libiberty/ChangeLog:

	PR c++/88115
	* cp-demangle.c (d_print_comp_inner)
	<case DEMANGLE_COMPONENT_EXTENDED_OPERATOR>: Don't print the
	"operator " prefix for __alignof__.
	<case DEMANGLE_COMPONENT_UNARY>: Always print parens around the
	operand of __alignof__.
	* testsuite/demangle-expected: Test demangling for __alignof__.

gcc/testsuite/ChangeLog:

	PR c++/88115
	* g++.dg/abi/macro0.C: Adjust.
	* g++.dg/cpp0x/alignof7.C: New test.
	* g++.dg/cpp0x/alignof8.C: New test.

1 files changed, 23 insertions, 4 deletions

diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 9fd3001..5548e51 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -3049,11 +3049,30 @@ write_expression (tree expr)
       else
 	goto normal_expr;
     }
-  else if (TREE_CODE (expr) == ALIGNOF_EXPR
-	   && TYPE_P (TREE_OPERAND (expr, 0)))
+  else if (TREE_CODE (expr) == ALIGNOF_EXPR)
     {
-      write_string ("at");
-      write_type (TREE_OPERAND (expr, 0));
+      if (!ALIGNOF_EXPR_STD_P (expr))
+	{
+	  if (abi_warn_or_compat_version_crosses (15))
+	    G.need_abi_warning = true;
+	  if (abi_version_at_least (15))
+	    {
+	      /* We used to mangle __alignof__ like alignof.  */
+	      write_string ("v111__alignof__");
+	      if (TYPE_P (TREE_OPERAND (expr, 0)))
+		write_type (TREE_OPERAND (expr, 0));
+	      else
+		write_expression (TREE_OPERAND (expr, 0));
+	      return;
+	    }
+	}
+      if (TYPE_P (TREE_OPERAND (expr, 0)))
+	{
+	  write_string ("at");
+	  write_type (TREE_OPERAND (expr, 0));
+	}
+      else
+	goto normal_expr;
     }
   else if (code == SCOPE_REF
 	   || code == BASELINK)