From: Eric Botcazou <ebotcazou@libertysurf.fr>
Date: Sat, 21 Dec 2002 20:31:15 +0000 (+0100)
Subject: re PR rtl-optimization/8599 (loop unroll bug with -march=k6-3)
X-Git-Tag: releases/gcc-3.2.2~161
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5402998384c858ca8e4a34ea12c80a6706852e6b;p=thirdparty%2Fgcc.git

re PR rtl-optimization/8599 (loop unroll bug with -march=k6-3)

	PR optimization/8599
	* doloop.c (doloop_modify_runtime): Fix loop count computation
	for preconditioned unrolled loops.

From-SVN: r60393
---

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 82630b7c41c9..fd31004539e2 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2002-12-21  Eric Botcazou  <ebotcazou@libertysurf.fr>
+
+	PR optimization/8599
+	* doloop.c (doloop_modify_runtime): Fix loop count computation
+	for preconditioned unrolled loops.
+
 2002-12-21  Eric Botcazou  <ebotcazou@libertysurf.fr>
 
 	PR optimization/8599
diff --git a/gcc/doloop.c b/gcc/doloop.c
index 06d8d5734853..25deb503717e 100644
--- a/gcc/doloop.c
+++ b/gcc/doloop.c
@@ -598,9 +598,13 @@ doloop_modify_runtime (loop, iterations_max,
 
      If the loop has been unrolled, the full calculation is
 
-       t1 = abs_inc * unroll_number;		increment per loop
-       n = abs (final - initial) / t1;		full loops
-       n += (abs (final - initial) % t1) != 0;	partial loop
+       t1 = abs_inc * unroll_number;		        increment per loop
+       n = (abs (final - initial) + abs_inc - 1) / t1;    full loops
+       n += ((abs (final - initial) + abs_inc - 1) % t1) >= abs_inc;
+                                                          partial loop
+     which works out to be equivalent to
+
+       n = (abs (final - initial) + t1 - 1) / t1;
 
      However, in certain cases the unrolled loop will be preconditioned
      by emitting copies of the loop body with conditional branches,
@@ -682,13 +686,15 @@ doloop_modify_runtime (loop, iterations_max,
       if (shift_count < 0)
 	abort ();
 
-      if (!loop_info->preconditioned)
+      if (loop_info->preconditioned)
+	diff = expand_simple_binop (GET_MODE (diff), PLUS,
+				    diff, GEN_INT (abs_inc - 1),
+				    diff, 1, OPTAB_LIB_WIDEN);
+      else
 	diff = expand_simple_binop (GET_MODE (diff), PLUS,
 				    diff, GEN_INT (abs_loop_inc - 1),
 				    diff, 1, OPTAB_LIB_WIDEN);
 
-      /* (abs (final - initial) + abs_inc * unroll_number - 1)
-	 / (abs_inc * unroll_number)  */
       diff = expand_simple_binop (GET_MODE (diff), LSHIFTRT,
 				  diff, GEN_INT (shift_count),
 				  diff, 1, OPTAB_LIB_WIDEN);