re PR tree-optimization/59038 (r204398 causes 186.crafty init.c to be miscompiled)

2013-11-08  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/59038
	PR tree-optimization/58955
	* tree-loop-distribution.c (pg_add_dependence_edges): Revert
	previous change.  Handle known dependences correctly.

	* gcc.dg/torture/pr59038.c: New testcase.

From-SVN: r204561

gcc/ChangeLog

+2013-11-08  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/59038
+	PR tree-optimization/58955
+	* tree-loop-distribution.c (pg_add_dependence_edges): Revert
+	previous change.  Handle known dependences correctly.
+
 2013-11-08  Tom de Vries  <tom@codesourcery.com>
 
 	* config/rs6000/t-xilinx: Remove duplicate contents.

gcc/testsuite/gcc.dg/torture/pr59038.c

+/* { dg-do run } */
+
+extern void abort (void);
+
+unsigned char first_ones_8bit[256];
+unsigned char connected_passed[256];
+
+int
+main ()
+{
+  int i, j;
+  for (i=0;i<256;i++){
+      connected_passed[i]=0;
+      first_ones_8bit[i]=0;
+      for (j=7;j>0;j--){
+	  if ((i & (3<<(7-j))) == (3<<(7-j))){
+	      connected_passed[i]=j;
+	      break;
+	  }
+      }
+  }
+  if (connected_passed[3] != 7)
+    abort ();
+  return 0;
+}

gcc/tree-loop-distribution.c

@@ -1324,7 +1324,7 @@ pg_add_dependence_edges (struct graph *rdg, vec<loop_p> loops, int dir,
   for (int ii = 0; drs1.iterate (ii, &dr1); ++ii)
     for (int jj = 0; drs2.iterate (jj, &dr2); ++jj)
       {
-	int this_dir = -1;
+	int this_dir = 1;
 	ddr_p ddr;
 	/* Re-shuffle data-refs to be in dominator order.  */
 	if (rdg_vertex_for_stmt (rdg, DR_STMT (dr1))
@@ -1350,8 +1350,17 @@ pg_add_dependence_edges (struct graph *rdg, vec<loop_p> loops, int dir,
 	      }
 	    /* Known dependences can still be unordered througout the
 	       iteration space, see gcc.dg/tree-ssa/ldist-16.c.  */
-	    if (DDR_NUM_DIST_VECTS (ddr) == 0)
+	    if (DDR_NUM_DIST_VECTS (ddr) != 1)
 	      this_dir = 2;
+	    /* If the overlap is exact preserve stmt order.  */
+	    else if (lambda_vector_zerop (DDR_DIST_VECT (ddr, 0), 1))
+	      ;
+	    else
+	      {
+		/* Else as the distance vector is lexicographic positive
+		   swap the dependence direction.  */
+		this_dir = -this_dir;
+	      }
 	  }
 	else
 	  this_dir = 0;