--- gcc/cfgexpand.c.jj	2011-01-03 09:54:28.000000000 +0100
+++ gcc/cfgexpand.c	2011-01-20 09:59:09.000000000 +0100
@@ -2567,6 +2567,13 @@ expand_debug_expr (tree exp)
 
       if (TREE_CODE (exp) == MEM_REF)
 	{
+	  if (GET_CODE (op0) == DEBUG_IMPLICIT_PTR
+	      || (GET_CODE (op0) == PLUS
+		  && GET_CODE (XEXP (op0, 0)) == DEBUG_IMPLICIT_PTR))
+	    /* (mem (debug_implicit_ptr)) might confuse aliasing.
+	       Instead just use get_inner_reference.  */
+	    goto component_ref;
+
 	  op1 = expand_debug_expr (TREE_OPERAND (exp, 1));
 	  if (!op1 || !CONST_INT_P (op1))
 	    return NULL;
@@ -2605,6 +2612,7 @@ expand_debug_expr (tree exp)
 
       return op0;
 
+    component_ref:
     case ARRAY_REF:
     case ARRAY_RANGE_REF:
     case COMPONENT_REF:
--- gcc/testsuite/g++.dg/debug/pr47283.C.jj	2011-01-20 10:11:09.000000000 +0100
+++ gcc/testsuite/g++.dg/debug/pr47283.C	2011-01-20 10:13:16.000000000 +0100
@@ -0,0 +1,58 @@
+// PR debug/47283
+// { dg-do compile }
+
+template <typename T> inline const T &
+f1 (const T &a, const T &b)
+{
+  if (a < b)
+    return b;
+  return a;
+};
+
+struct A
+{
+  A (int w, int h) { a1 = w; }
+  A f2 (const A &) const;
+  int a1, a2;
+};
+
+inline A
+A::f2 (const A &x) const
+{
+  return A (f1 (a1, x.a1), f1 (a2, x.a2));
+};
+
+struct B
+{
+  A f3 () const;
+  void f4 (const A &) { b2 = 5 + b1; }
+  int b1, b2;
+};
+
+struct C
+{
+};
+
+struct D
+{
+  virtual C f5 (const C &) const;
+};
+
+struct E
+{
+  C f6 () const;
+  int f7 () const;
+  virtual B f8 (const C &) const;
+  A f9 () const;
+  virtual void f10 ();
+  struct F { D *h; } *d;
+};
+
+void
+E::f10 ()
+{
+  const C c = d->h->f5 (f6 ());
+  B b = f8 (c);
+  b.f4 (b.f3 ().f2 (f9 ()));
+  f7 ();
+}