[backport from gcc-4.8/trunk r188733 <mikpe@it.uu.se>]

gcc/

2012-06-18  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/53693
	* tree-vect-patterns.c (vect_operation_fits_smaller_type):
	Reject operands with more than one use.

gcc/testsuite/

2012-06-18  Richard Guenther  <rguenther@suse.de>

	PR tree-optimization/53693
	* g++.dg/torture/pr53693.C: New testcase.

--- gcc-4.7.1/gcc/testsuite/g++.dg/torture/pr53693.C.~1~	1970-01-01 01:00:00.000000000 +0100
+++ gcc-4.7.1/gcc/testsuite/g++.dg/torture/pr53693.C	2012-06-24 11:48:40.000000000 +0200
@@ -0,0 +1,21 @@
+// { dg-do compile }
+
+void
+filter_scanlines (void *src_buffer, void *dst_buffer, int dst_pitch, int width)
+{
+  int x;
+  unsigned short *src, *dst_a, *dst_b;
+
+  src = (unsigned short *) src_buffer;
+  dst_a = (unsigned short *) dst_buffer;
+  dst_b = ((unsigned short *) dst_buffer) + (dst_pitch >> 1);
+
+  for (x = 0; x < width; x++)
+    {
+      unsigned char gs, gh;
+      gs = src[x];
+      gh = gs + (gs >> 1);
+      dst_a[x] = (gh << 5) | (gh);
+      dst_b[x] = ((gs  - gh) << 5)  | (gs  - gh);
+    }
+}
--- gcc-4.7.1/gcc/tree-vect-patterns.c.~1~	2012-05-04 22:59:13.000000000 +0200
+++ gcc-4.7.1/gcc/tree-vect-patterns.c	2012-06-24 11:48:40.000000000 +0200
@@ -937,6 +937,11 @@ vect_operation_fits_smaller_type (gimple
       || TREE_CODE (const_oprnd) != INTEGER_CST)
     return false;
 
+  /* If oprnd has other uses besides that in stmt we cannot mark it
+     as being part of a pattern only.  */
+  if (!has_single_use (oprnd))
+    return false;
+
   /* If we are in the middle of a sequence, we use DEF from a previous
      statement.  Otherwise, OPRND has to be a result of type promotion.  */
   if (*new_type)