re PR tree-optimization/77937 (ICE: in replace_one_candidate, at…

re PR tree-optimization/77937 (ICE: in replace_one_candidate, at gimple-ssa-strength-reduction.c:3370)

2016-10-13  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR tree-optimization/77937
	* gimple-ssa-strength-reduction.c (analyze_increments): Set cost
	to infinite when we have a pointer with an increment of -1.

From-SVN: r241125

gcc/ChangeLog

+2016-10-13  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
+
+	PR tree-optimization/77937
+	* gimple-ssa-strength-reduction.c (analyze_increments): Set cost
+	to infinite when we have a pointer with an increment of -1.
+
 2016-10-13  Thomas Preud'homme  <thomas.preudhomme@arm.com>
 
 	* coretypes.h: Move MEMMODEL_* macros and enum memmodel definition

gcc/gimple-ssa-strength-reduction.c

@@ -2819,6 +2819,11 @@ analyze_increments (slsr_cand_t first_dep, machine_mode mode, bool speed)
 		   && !POINTER_TYPE_P (first_dep->cand_type)))
 	incr_vec[i].cost = COST_NEUTRAL;
 
+      /* FIXME: We don't handle pointers with a -1 increment yet.
+         They are usually unprofitable anyway.  */
+      else if (incr == -1 && POINTER_TYPE_P (first_dep->cand_type))
+	incr_vec[i].cost = COST_INFINITE;
+      
       /* FORNOW: If we need to add an initializer, give up if a cast from
 	 the candidate's type to its stride's type can lose precision.
 	 This could eventually be handled better by expressly retaining the