--- gcc/c-family/c-common.c.jj	2012-12-31 15:05:45.000000000 +0100
+++ gcc/c-family/c-common.c	2013-01-08 15:15:47.019347593 +0100
@@ -1269,6 +1269,25 @@ c_fully_fold_internal (tree expr, bool i
 	  && !TREE_OVERFLOW_P (op0)
 	  && !TREE_OVERFLOW_P (op1))
 	overflow_warning (EXPR_LOCATION (expr), ret);
+      if ((code == LSHIFT_EXPR || code == RSHIFT_EXPR)
+	  && TREE_CODE (orig_op1) != INTEGER_CST
+	  && TREE_CODE (op1) == INTEGER_CST
+	  && (TREE_CODE (TREE_TYPE (orig_op0)) == INTEGER_TYPE
+	      || TREE_CODE (TREE_TYPE (orig_op0)) == FIXED_POINT_TYPE)
+	  && TREE_CODE (TREE_TYPE (orig_op1)) == INTEGER_TYPE
+	  && c_inhibit_evaluation_warnings == 0)
+	{
+	  if (tree_int_cst_sgn (op1) < 0)
+	    warning_at (loc, 0, (code == LSHIFT_EXPR
+				 ? "left shift count is negative"
+				 : "right shift count is negative"));
+	  else if (compare_tree_int (op1,
+				     TYPE_PRECISION (TREE_TYPE (orig_op0)))
+		   >= 0)
+	    warning_at (loc, 0, (code == LSHIFT_EXPR
+				 ? "left shift count >= width of type"
+				 : "right shift count >= width of type"));
+	}
       goto out;
 
     case INDIRECT_REF:
--- gcc/cp/typeck.c.jj	2013-01-07 14:14:44.000000000 +0100
+++ gcc/cp/typeck.c	2013-01-08 15:30:20.202388635 +0100
@@ -4095,10 +4095,13 @@ cp_build_binary_op (location_t location,
 	}
       else if (code0 == INTEGER_TYPE && code1 == INTEGER_TYPE)
 	{
+	  tree const_op1 = maybe_constant_value (op1);
+	  if (TREE_CODE (const_op1) != INTEGER_CST)
+	    const_op1 = op1;
 	  result_type = type0;
-	  if (TREE_CODE (op1) == INTEGER_CST)
+	  if (TREE_CODE (const_op1) == INTEGER_CST)
 	    {
-	      if (tree_int_cst_lt (op1, integer_zero_node))
+	      if (tree_int_cst_lt (const_op1, integer_zero_node))
 		{
 		  if ((complain & tf_warning)
 		      && c_inhibit_evaluation_warnings == 0)
@@ -4106,7 +4109,7 @@ cp_build_binary_op (location_t location,
 		}
 	      else
 		{
-		  if (compare_tree_int (op1, TYPE_PRECISION (type0)) >= 0
+		  if (compare_tree_int (const_op1, TYPE_PRECISION (type0)) >= 0
 		      && (complain & tf_warning)
 		      && c_inhibit_evaluation_warnings == 0)
 		    warning (0, "right shift count >= width of type");
@@ -4138,16 +4141,20 @@ cp_build_binary_op (location_t location,
 	}
       else if (code0 == INTEGER_TYPE && code1 == INTEGER_TYPE)
 	{
+	  tree const_op1 = maybe_constant_value (op1);
+	  if (TREE_CODE (const_op1) != INTEGER_CST)
+	    const_op1 = op1;
 	  result_type = type0;
-	  if (TREE_CODE (op1) == INTEGER_CST)
+	  if (TREE_CODE (const_op1) == INTEGER_CST)
 	    {
-	      if (tree_int_cst_lt (op1, integer_zero_node))
+	      if (tree_int_cst_lt (const_op1, integer_zero_node))
 		{
 		  if ((complain & tf_warning)
 		      && c_inhibit_evaluation_warnings == 0)
 		    warning (0, "left shift count is negative");
 		}
-	      else if (compare_tree_int (op1, TYPE_PRECISION (type0)) >= 0)
+	      else if (compare_tree_int (const_op1,
+					 TYPE_PRECISION (type0)) >= 0)
 		{
 		  if ((complain & tf_warning)
 		      && c_inhibit_evaluation_warnings == 0)
--- gcc/testsuite/c-c++-common/pr48418.c.jj	2013-01-08 15:25:36.501003969 +0100
+++ gcc/testsuite/c-c++-common/pr48418.c	2013-01-08 15:21:54.000000000 +0100
@@ -0,0 +1,20 @@
+/* PR c/48418 */
+/* { dg-do compile } */
+/* { dg-options "-Wall -O2" } */
+
+int
+foo (int x)
+{
+  const int a = sizeof (int) * __CHAR_BIT__;
+  const int b = -7;
+  int c = 0;
+  c += x << a;				   /* { dg-warning "left shift count >= width of type" } */
+  c += x << b;				   /* { dg-warning "left shift count is negative" } */
+  c += x << (sizeof (int) * __CHAR_BIT__); /* { dg-warning "left shift count >= width of type" } */
+  c += x << -7;				   /* { dg-warning "left shift count is negative" } */
+  c += x >> a;				   /* { dg-warning "right shift count >= width of type" } */
+  c += x >> b;				   /* { dg-warning "right shift count is negative" } */
+  c += x >> (sizeof (int) * __CHAR_BIT__); /* { dg-warning "right shift count >= width of type" } */
+  c += x >> -7;				   /* { dg-warning "right shift count is negative" } */
+  return c;
+}