(combine_givs): Improve combining DEST_REG giv with its only use.

From-SVN: r12769

diff --git a/gcc/loop.c b/gcc/loop.c
index f4670fd073561a66760caecde8dc5d6651be8827..b3c49a4dd03ceed62c6419d47e908f7e58024269 100644 (file)
--- a/gcc/loop.c
+++ b/gcc/loop.c
@@ -1,5 +1,5 @@
 /* Perform various loop optimizations, including strength reduction.
-   Copyright (C) 1987, 88, 89, 91-4, 1995 Free Software Foundation, Inc.
+   Copyright (C) 1987, 88, 89, 91-5, 1996 Free Software Foundation, Inc.
 
 This file is part of GNU CC.
 
@@ -5672,14 +5672,26 @@ combine_givs (bl)
                /* g2->new_reg set by `combine_givs_p'  */
                g2->same = g1;
                g1->combined_with = 1;
-               g1->benefit += g2->benefit;
+
+               /* If one of these givs is a DEST_REG that was only used
+                  once, by the other giv, this is actually a single use.  */
+               if ((g1->giv_type != DEST_REG
+                    || n_times_used[REGNO (g1->dest_reg)] != 1
+                    || ! reg_mentioned_p (g1->dest_reg, PATTERN (g2->insn)))
+                   && (g2->giv_type != DEST_REG
+                       || n_times_used[REGNO (g2->dest_reg)] != 1
+                       || ! reg_mentioned_p (g2->dest_reg,
+                                             PATTERN (g1->insn))))
+                 {
+                   g1->benefit += g2->benefit;
+                   g1->times_used += g2->times_used;
+                 }
                /* ??? The new final_[bg]iv_value code does a much better job
                   of finding replaceable giv's, and hence this code may no
                   longer be necessary.  */
                if (! g2->replaceable && REG_USERVAR_P (g2->dest_reg))
                  g1->benefit -= copy_cost;
                g1->lifetime += g2->lifetime;
-               g1->times_used += g2->times_used;
                
                if (loop_dump_stream)
                  fprintf (loop_dump_stream, "giv at %d combined with giv at %d\n",