From patchwork Tue Oct  9 09:36:59 2012
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Subject: Fix my change to unroll_loop_constant_iterations
From: Jan Hubicka <hubicka@ucw.cz>
X-Patchwork-Id: 190249
Message-Id: <20121009093659.GA14364@kam.mff.cuni.cz>
To: Jan Hubicka <hubicka@ucw.cz>
Cc: gcc-patches@gcc.gnu.org
Date: Tue, 9 Oct 2012 11:36:59 +0200

> H,
> I hope this change is responsible for today misoptimizations of SPEC at -O3.
> While updating unroll_loop_constant_iterations and fighting with double_int
> operations I made two trivial mistakes.
> 
> I am bootstrapping/regtesting the following and will commit it as obvious if
> it passes.
> 
> Honza
> 
> 	* loop-unroll.c (unroll_loop_constant_iterations): Fix previous patch.

Unforutnately there is one other case where one has to be extra cureful about overflows.
This is in fact latent bug in the unroller, but it now reproduce with -O3 -fpeel-loops
bootstrap because estimates tends to be close to maximum of the integer types.

I am re-starting testing with the following patch and will commit if passes
(but i will be till 2pm on bus).
My apologizes for the breakage.

Honza

Index: loop-unroll.c
===================================================================
--- loop-unroll.c	(revision 192240)
+++ loop-unroll.c	(working copy)
@@ -740,6 +740,7 @@ unroll_loop_constant_iterations (struct
   	    apply_opt_in_copies (opt_info, exit_mod + 1, false, false);
 
 	  desc->niter -= exit_mod + 1;
+	  loop->nb_iterations_upper_bound -= double_int::from_uhwi (exit_mod + 1);
 	  if (loop->any_estimate
 	      && double_int::from_uhwi (exit_mod + 1).ule
 	           (loop->nb_iterations_estimate))
@@ -795,12 +796,12 @@ unroll_loop_constant_iterations (struct
 
   desc->niter /= max_unroll + 1;
   loop->nb_iterations_upper_bound
-    = loop->nb_iterations_upper_bound.udiv (double_int::from_uhwi (exit_mod
+    = loop->nb_iterations_upper_bound.udiv (double_int::from_uhwi (max_unroll
 								   + 1),
 					    FLOOR_DIV_EXPR);
   if (loop->any_estimate)
     loop->nb_iterations_estimate
-      = loop->nb_iterations_estimate.udiv (double_int::from_uhwi (exit_mod
+      = loop->nb_iterations_estimate.udiv (double_int::from_uhwi (max_unroll
 							          + 1),
 				           FLOOR_DIV_EXPR);
   desc->niter_expr = GEN_INT (desc->niter);
@@ -879,8 +880,7 @@ decide_unroll_runtime_iterations (struct
   /* If we have profile feedback, check whether the loop rolls.  */
   if ((estimated_loop_iterations (loop, &iterations)
        || max_loop_iterations (loop, &iterations))
-      && iterations.fits_shwi ()
-      && iterations.to_shwi () <= 2 * nunroll)
+      && iterations.ule (double_int::from_shwi (2 * nunroll)))
     {
       if (dump_file)
 	fprintf (dump_file, ";; Not unrolling loop, doesn't roll\n");
@@ -1280,8 +1280,7 @@ decide_peel_simple (struct loop *loop, i
   /* If we have realistic estimate on number of iterations, use it.  */
   if (estimated_loop_iterations (loop, &iterations))
     {
-      if (!iterations.fits_shwi ()
-	  || iterations.to_shwi () + 1 > npeel)
+      if (double_int::from_shwi (npeel).ule (iterations))
 	{
 	  if (dump_file)
 	    {
@@ -1298,8 +1297,7 @@ decide_peel_simple (struct loop *loop, i
   /* If we have small enough bound on iterations, we can still peel (completely
      unroll).  */
   else if (max_loop_iterations (loop, &iterations)
-           && iterations.fits_shwi ()
-           && iterations.to_shwi () + 1 <= npeel)
+           && iterations.ult (double_int::from_shwi (npeel)))
     npeel = iterations.to_shwi () + 1;
   else
     {
@@ -1449,8 +1447,7 @@ decide_unroll_stupid (struct loop *loop,
   /* If we have profile feedback, check whether the loop rolls.  */
   if ((estimated_loop_iterations (loop, &iterations)
        || max_loop_iterations (loop, &iterations))
-      && iterations.fits_shwi ()
-      && iterations.to_shwi () <= 2 * nunroll)
+      && iterations.ule (double_int::from_shwi (2 * nunroll)))
     {
       if (dump_file)
 	fprintf (dump_file, ";; Not unrolling loop, doesn't roll\n");