gimple-ssa-strength-reduction.c (analyze_increments): Distinguish replacement…

gimple-ssa-strength-reduction.c (analyze_increments): Distinguish replacement costs for constant strides from those for unknown strides.

2017-12-14  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	* gimple-ssa-strength-reduction.c (analyze_increments):
	Distinguish replacement costs for constant strides from those for
	unknown strides.

From-SVN: r255664

gcc/ChangeLog

+2017-12-14  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
+
+	* gimple-ssa-strength-reduction.c (analyze_increments):
+	Distinguish replacement costs for constant strides from those for
+	unknown strides.
+
 2017-12-14  Jakub Jelinek  <jakub@redhat.com>
 
 	* var-tracking.c (variable_tracking_main_1): Formatting fix.

gcc/gimple-ssa-strength-reduction.c

@@ -3083,7 +3083,17 @@ analyze_increments (slsr_cand_t first_dep, machine_mode mode, bool speed)
       else if (first_dep->kind == CAND_MULT)
 	{
 	  int cost = mult_by_coeff_cost (incr, mode, speed);
-	  int repl_savings = mul_cost (speed, mode) - add_cost (speed, mode);
+	  int repl_savings;
+
+	  if (tree_fits_shwi_p (first_dep->stride))
+	    {
+	      HOST_WIDE_INT hwi_stride = tree_to_shwi (first_dep->stride);
+	      repl_savings = mult_by_coeff_cost (hwi_stride, mode, speed);
+	    }
+	  else
+	    repl_savings = mul_cost (speed, mode);
+	  repl_savings -= add_cost (speed, mode);
+
 	  if (speed)
 	    cost = lowest_cost_path (cost, repl_savings, first_dep,
 				     incr_vec[i].incr, COUNT_PHIS);