[PATCH] Fix PR53693

[Richard Guenther <rguenther at suse dot de>]

When the vectorizer detects a widening shift pattern it has to
make sure the widening operation is used only once as it will
make it part of the recognized pattern.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Richard.

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.

	* g++.dg/torture/pr53693.C: New testcase.

Index: gcc/tree-vect-patterns.c
===================================================================
*** gcc/tree-vect-patterns.c	(revision 188725)
--- gcc/tree-vect-patterns.c	(working copy)
*************** vect_operation_fits_smaller_type (gimple
*** 991,996 ****
--- 991,1001 ----
        || 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)
Index: gcc/testsuite/g++.dg/torture/pr53693.C
===================================================================
*** gcc/testsuite/g++.dg/torture/pr53693.C	(revision 0)
--- gcc/testsuite/g++.dg/torture/pr53693.C	(revision 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);
+     }
+ }