loop.c (strength_reduce): Adjust BENEFIT appropriately if an autoincrement memory...

        * loop.c (strength_reduce): Adjust BENEFIT appropriately if an
        autoincrement memory reference will eliminate add insns.

From-SVN: r13717

diff --git a/gcc/loop.c b/gcc/loop.c
index 0ea4f2026162aa00648a0997a394cdb5db45c8ed..3e7bb58e3e37827a8a6e706599e05b2af290305e 100644 (file)
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -3850,9 +3850,23 @@ strength_reduce (scan_start, end, loop_top, insn_count,
             unchanged (recompute it from the biv each time it is used).
             This decision can be made independently for each giv.  */
 
-         /* ??? Perhaps attempt to guess whether autoincrement will handle
-            some of the new add insns; if so, can increase BENEFIT
-            (undo the subtraction of add_cost that was done above).  */
+#ifdef AUTO_INC_DEC
+         /* Attempt to guess whether autoincrement will handle some of the
+            new add insns; if so, increase BENEFIT (undo the subtraction of
+            add_cost that was done above).  */
+         if (v->giv_type == DEST_ADDR
+             && GET_CODE (v->mult_val) == CONST_INT)
+           {
+#if defined (HAVE_POST_INCREMENT) || defined (HAVE_PRE_INCREMENT)
+             if (INTVAL (v->mult_val) == GET_MODE_SIZE (v->mem_mode))
+               benefit += add_cost * bl->biv_count;
+#endif
+#if defined (HAVE_POST_DECREMENT) || defined (HAVE_PRE_DECREMENT)
+             if (-INTVAL (v->mult_val) == GET_MODE_SIZE (v->mem_mode))
+               benefit += add_cost * bl->biv_count;
+#endif
+           }
+#endif
 
          /* If an insn is not to be strength reduced, then set its ignore
             flag, and clear all_reduced.  */