Leaving value-dependent expressions alone doesn't work if you then
silently turn them into error_mark_node because they aren't INTEGER_CST.
And while I'm in this code, there's no need to check the result of
cxx_constant_value, as it already returns error_mark_node for
non-constant expressions.
Tested x86_64-pc-linux-gnu, applying to trunk and 4.8.
commit 66d07cda5155f2713de7f5e85a37062210c7c0b4
Author: Jason Merrill <ja...@redhat.com>
Date: Wed Apr 24 21:13:50 2013 -0400
PR c++/56859
* typeck.c (cxx_alignas_expr): Handle value-dependence properly.
diff --git a/gcc/cp/typeck.c b/gcc/cp/typeck.c
index 84da5de..b761dd5 100644
--- a/gcc/cp/typeck.c
+++ b/gcc/cp/typeck.c
@@ -1725,15 +1725,19 @@ cxx_alignas_expr (tree e)
When the alignment-specifier is of the form
alignas(type-id ), it shall have the same effect as
- alignas( alignof(type-id )). */
+ alignas(alignof(type-id )). */
return cxx_sizeof_or_alignof_type (e, ALIGNOF_EXPR, false);
-
/* If we reach this point, it means the alignas expression if of
the form "alignas(assignment-expression)", so we should follow
what is stated by [dcl.align]/2. */
+ if (value_dependent_expression_p (e))
+ /* Leave value-dependent expression alone for now. */
+ return e;
+
+ e = fold_non_dependent_expr (e);
e = mark_rvalue_use (e);
/* [dcl.align]/2 says:
@@ -1741,18 +1745,7 @@ cxx_alignas_expr (tree e)
the assignment-expression shall be an integral constant
expression. */
- e = fold_non_dependent_expr (e);
- if (value_dependent_expression_p (e))
- /* Leave value-dependent expression alone for now. */;
- else
- e = cxx_constant_value (e);
-
- if (e == NULL_TREE
- || e == error_mark_node
- || TREE_CODE (e) != INTEGER_CST)
- return error_mark_node;
-
- return e;
+ return cxx_constant_value (e);
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/gen-attrs-54.C b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-54.C
new file mode 100644
index 0000000..45aa8e4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/gen-attrs-54.C
@@ -0,0 +1,14 @@
+// PR c++/56859
+// { dg-require-effective-target c++11 }
+
+template<unsigned size, unsigned alignment>
+struct aligned_storage
+{
+ using type = struct { alignas(alignment) unsigned char data[size]; };
+};
+
+#define SA(X) static_assert((X),#X)
+SA(alignof(aligned_storage<8,1>::type) == 1);
+SA(alignof(aligned_storage<8,2>::type) == 2);
+SA(alignof(aligned_storage<8,4>::type) == 4);
+SA(alignof(aligned_storage<8,8>::type) == 8);
