From: Kazu Hirata <kazu@codesourcery.com>
Date: Sun, 3 May 2009 23:31:18 +0000 (+0000)
Subject: expmed.c (synth_mult): When trying out a shift, pass the result of a signed shift.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=ddc2690ac0b80de267c5046b524638a40a24d572;p=gcc.git

expmed.c (synth_mult): When trying out a shift, pass the result of a signed shift.

	* expmed.c (synth_mult): When trying out a shift, pass the result
	of a signed shift.

From-SVN: r147087
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index b67be5b78e0..dcc0070b232 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2009-05-04  Kazu Hirata  <kazu@codesourcery.com>
+
+	* expmed.c (synth_mult): When trying out a shift, pass the result
+	of a signed shift.
+
 2009-05-04  Kazu Hirata  <kazu@codesourcery.com>
 
 	* expmed.c (shiftsub_cost): Rename to shiftsub0_cost.
diff --git a/gcc/expmed.c b/gcc/expmed.c
index 7ffb693dcdd..d0c1621cc5e 100644
--- a/gcc/expmed.c
+++ b/gcc/expmed.c
@@ -2551,6 +2551,38 @@ synth_mult (struct algorithm *alg_out, unsigned HOST_WIDE_INT t,
 	      best_alg->log[best_alg->ops] = m;
 	      best_alg->op[best_alg->ops] = alg_shift;
 	    }
+
+	  /* See if treating ORIG_T as a signed number yields a better
+	     sequence.  Try this sequence only for a negative ORIG_T
+	     as it would be useless for a non-negative ORIG_T.  */
+	  if ((HOST_WIDE_INT) orig_t < 0)
+	    {
+	      /* Shift ORIG_T as follows because a right shift of a
+		 negative-valued signed type is implementation
+		 defined.  */
+	      q = ~(~orig_t >> m);
+	      /* The function expand_shift will choose between a shift
+		 and a sequence of additions, so the observed cost is
+		 given as MIN (m * add_cost[speed][mode],
+		 shift_cost[speed][mode][m]).  */
+	      op_cost = m * add_cost[speed][mode];
+	      if (shift_cost[speed][mode][m] < op_cost)
+		op_cost = shift_cost[speed][mode][m];
+	      new_limit.cost = best_cost.cost - op_cost;
+	      new_limit.latency = best_cost.latency - op_cost;
+	      synth_mult (alg_in, q, &new_limit, mode);
+
+	      alg_in->cost.cost += op_cost;
+	      alg_in->cost.latency += op_cost;
+	      if (CHEAPER_MULT_COST (&alg_in->cost, &best_cost))
+		{
+		  struct algorithm *x;
+		  best_cost = alg_in->cost;
+		  x = alg_in, alg_in = best_alg, best_alg = x;
+		  best_alg->log[best_alg->ops] = m;
+		  best_alg->op[best_alg->ops] = alg_shift;
+		}
+	    }
 	}
       if (cache_hit)
 	goto done;