commit 1499daa7ea067fd905536a5ead1876107c8fbbc5
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Dec 21 13:42:30 2011 -0500

    	PR c++/51611
    	* cp-tree.h (CONVERT_EXPR_VBASE_PATH): New.
    	* class.c (build_base_path): Defer vbase conversion in an NSDMI.
    	* tree.c (bot_replace): Expand it here.
    	* cp-gimplify.c (cp_genericize_r): Make sure deferred conversion
    	doesn't leak into GENERIC.

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index c96f7bf..79686a2 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -318,6 +318,19 @@ build_base_path (enum tree_code code,
       return expr;
     }
 
+  /* If we're in an NSDMI, we don't have the full constructor context yet
+     that we need for converting to a virtual base, so just build a stub
+     CONVERT_EXPR and expand it later in bot_replace.  */
+  if (virtual_access && fixed_type_p < 0
+      && current_scope () != current_function_decl)
+    {
+      expr = build1 (CONVERT_EXPR, ptr_target_type, expr);
+      CONVERT_EXPR_VBASE_PATH (expr) = true;
+      if (!want_pointer)
+	expr = build_indirect_ref (EXPR_LOCATION (expr), expr, RO_NULL);
+      return expr;
+    }
+
   /* Do we need to check for a null pointer?  */
   if (want_pointer && !nonnull)
     {
diff --git a/gcc/cp/cp-gimplify.c b/gcc/cp/cp-gimplify.c
index c68069d..e06c545 100644
--- a/gcc/cp/cp-gimplify.c
+++ b/gcc/cp/cp-gimplify.c
@@ -1100,6 +1100,8 @@ cp_genericize_r (tree *stmt_p, int *walk_subtrees, void *data)
       wtd->omp_ctx = omp_ctx.outer;
       splay_tree_delete (omp_ctx.variables);
     }
+  else if (TREE_CODE (stmt) == CONVERT_EXPR)
+    gcc_assert (!CONVERT_EXPR_VBASE_PATH (stmt));
 
   pointer_set_insert (p_set, *stmt_p);
 
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 633b6b4..6e62bd1 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -74,6 +74,7 @@ c-common.h, not after.
       DECL_OVERRIDE_P (in FUNCTION_DECL)
       IMPLICIT_CONV_EXPR_DIRECT_INIT (in IMPLICIT_CONV_EXPR)
       TRANSACTION_EXPR_IS_STMT (in TRANSACTION_EXPR)
+      CONVERT_EXPR_VBASE_PATH (in CONVERT_EXPR)
    1: IDENTIFIER_VIRTUAL_P (in IDENTIFIER_NODE)
       TI_PENDING_TEMPLATE_FLAG.
       TEMPLATE_PARMS_FOR_INLINE.
@@ -4011,6 +4012,11 @@ more_aggr_init_expr_args_p (const aggr_init_expr_arg_iterator *iter)
   (TREE_CODE (EXPR) == TARGET_EXPR && TREE_LANG_FLAG_2 (EXPR)		\
    && same_type_ignoring_top_level_qualifiers_p (TYPE, TREE_TYPE (EXPR)))
 
+/* True if this CONVERT_EXPR is for a conversion to virtual base in
+   an NSDMI, and should be re-evaluated when used in a constructor.  */
+#define CONVERT_EXPR_VBASE_PATH(NODE) \
+  TREE_LANG_FLAG_0 (CONVERT_EXPR_CHECK (NODE))
+
 /* An enumeration of the kind of tags that C++ accepts.  */
 enum tag_types {
   none_type = 0, /* Not a tag type.  */
diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index aabe863..634c267 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -1944,6 +1944,20 @@ bot_replace (tree* t,
 	 parsing with the real one for this function.  */
       *t = current_class_ptr;
     }
+  else if (TREE_CODE (*t) == CONVERT_EXPR
+	   && CONVERT_EXPR_VBASE_PATH (*t))
+    {
+      /* In an NSDMI build_base_path defers building conversions to virtual
+	 bases, and we handle it here.  */
+      tree basetype = TYPE_MAIN_VARIANT (TREE_TYPE (TREE_TYPE (*t)));
+      VEC(tree,gc) *vbases = CLASSTYPE_VBASECLASSES (current_class_type);
+      int i; tree binfo;
+      FOR_EACH_VEC_ELT (tree, vbases, i, binfo)
+	if (BINFO_TYPE (binfo) == basetype)
+	  break;
+      *t = build_base_path (PLUS_EXPR, TREE_OPERAND (*t, 0), binfo, true,
+			    tf_warning_or_error);
+    }
 
   return NULL_TREE;
 }
diff --git a/gcc/testsuite/g++.dg/cpp0x/nsdmi-virtual1.C b/gcc/testsuite/g++.dg/cpp0x/nsdmi-virtual1.C
new file mode 100644
index 0000000..4aa8d48
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/nsdmi-virtual1.C
@@ -0,0 +1,26 @@
+// PR c++/51611
+// { dg-options -std=c++0x }
+// { dg-do run }
+
+struct A
+{
+  A(): i(42) { }
+  int i;
+  int f() { return i; }
+};
+
+struct B : virtual A
+{
+  int j = i + f();
+  int k = A::i + A::f();
+};
+
+struct C: B { int pad; };
+
+int main()
+{
+  C c;
+  if (c.j != 84 || c.k != 84)
+    __builtin_abort();
+}
+
