[C++ Patch] PR 31671

[Paolo Carlini]

Hi,

I think that in order to resolve this very old accepts-invalid, we can 
simply adjust the expr to the cv-qualifiers of probe_type. I also double 
checked that thing are fine for other combinations of cv-qualified 
reference types as parameter and as argument.

Tested x86_64-linux.

Thanks,
Paolo.

////////////////////
/cp
2013-10-10  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/31671
        * pt.c (convert_nontype_argument): Adjust TREE_TYPE (expr) to
        the cv-qualifiers of TREE_TYPE (probe_type).

/testsuite
2013-10-10  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/31671
        * g++.dg/template/nontype26.C: New.
Index: cp/pt.c
===================================================================
--- cp/pt.c     (revision 203341)
+++ cp/pt.c     (working copy)
@@ -5611,7 +5611,8 @@ convert_nontype_argument (tree type, tree expr, ts
                   TREE_TYPE (TREE_TYPE (addr)))))
            {
              expr = TREE_OPERAND (addr, 0);
-             expr_type = TREE_TYPE (expr);
+             expr_type = TREE_TYPE (expr) = cp_build_qualified_type
+               (TREE_TYPE (expr), cp_type_quals (TREE_TYPE (probe_type)));
            }
        }
     }
Index: testsuite/g++.dg/template/nontype26.C
===================================================================
--- testsuite/g++.dg/template/nontype26.C       (revision 0)
+++ testsuite/g++.dg/template/nontype26.C       (working copy)
@@ -0,0 +1,20 @@
+// PR c++/31671
+
+template<int& i> void doit() {
+  i = 0;
+}
+
+template<const int& i> class X {
+public:
+    void foo() {
+      doit<i>();  // { dg-error "cv-qualification|no matching" }
+    }
+};
+
+int i = 0;
+
+X<i> x;
+
+int main() {
+  x.foo();
+}