re PR tree-optimization/57051 (Optimization regression in 4.8.0 from 4.7.2)

	PR tree-optimization/57051
	* fold-const.c (const_binop): Handle VEC_LSHIFT_EXPR
	and VEC_RSHIFT_EXPR if shift count is a multiple of element
	bitsize.

From-SVN: r198339

gcc/ChangeLog

+2013-04-26  Jakub Jelinek  <jakub@redhat.com>
+
+	PR tree-optimization/57051
+	* fold-const.c (const_binop): Handle VEC_LSHIFT_EXPR
+	and VEC_RSHIFT_EXPR if shift count is a multiple of element
+	bitsize.
+
 2013-04-26  Richard Biener  <rguenther@suse.de>
 
 	* omp-low.c (finalize_task_copyfn): Do not drop PROP_loops.

gcc/fold-const.c

@@ -1380,6 +1380,31 @@ const_binop (enum tree_code code, tree arg1, tree arg2)
       int count = TYPE_VECTOR_SUBPARTS (type), i;
       tree *elts = XALLOCAVEC (tree, count);
 
+      if (code == VEC_LSHIFT_EXPR
+	  || code == VEC_RSHIFT_EXPR)
+	{
+	  if (!host_integerp (arg2, 1))
+	    return NULL_TREE;
+
+	  unsigned HOST_WIDE_INT shiftc = tree_low_cst (arg2, 1);
+	  unsigned HOST_WIDE_INT outerc = tree_low_cst (TYPE_SIZE (type), 1);
+	  unsigned HOST_WIDE_INT innerc
+	    = tree_low_cst (TYPE_SIZE (TREE_TYPE (type)), 1);
+	  if (shiftc >= outerc || (shiftc % innerc) != 0)
+	    return NULL_TREE;
+	  int offset = shiftc / innerc;
+	  if (code == VEC_LSHIFT_EXPR)
+	    offset = -offset;
+	  tree zero = build_zero_cst (TREE_TYPE (type));
+	  for (i = 0; i < count; i++)
+	    {
+	      if (i + offset < 0 || i + offset >= count)
+		elts[i] = zero;
+	      else
+		elts[i] = VECTOR_CST_ELT (arg1, i + offset);
+	    }
+	}
+      else
 	for (i = 0; i < count; i++)
 	  {
 	    tree elem1 = VECTOR_CST_ELT (arg1, i);