RE: [patch, PR44297] prefetch improvements to fix 465.tonto from non-constant step prefetching

["Fang, Changpeng" <Changpeng dot Fang at amd dot com>]

Hi, Nathan:

Thanks for pointing out. Here is the attachment.
(Zdenek sent me the same notice and I replied to send the attachment, unfortunately,
reply is off the mailing list).

Thanks,

Changpeng


________________________________________
From: Nathan Froyd [froydnj@codesourcery.com]
Sent: Monday, June 07, 2010 6:12 PM
To: Fang, Changpeng
Cc: Zdenek Dvorak; gcc-patches@gcc.gnu.org; sebpop@gmail.com
Subject: Re: [patch, PR44297] prefetch improvements to fix 465.tonto from       non-constant step prefetching

On Mon, Jun 07, 2010 at 05:26:58PM -0500, Fang, Changpeng wrote:
> Attached is the patch to fix 465/tonto regression (> 9%) caused (or
> exposed) by non-constant step prefetching.

You did not attach the patch.

-Nathan

From 989d719dec43195efdffce4e3dce90d3c291f9b1 Mon Sep 17 00:00:00 2001
From: Changpeng Fang <chfang@houghton.(none)>
Date: Mon, 7 Jun 2010 14:57:27 -0700
Subject: [PATCH 2/2] Account prefetch_mod and unroll_factor for the computation of the prefetch count

	*tree-ssa-loop-prefetch.c (estimate_prefetch_count): use prefetch_mod
	and unroll_factor to estimate the prefetch_count.
	(loop_prefetch_arrays): re-estimate the prefetch count by considering
	the unroll_factor and prefetch_mod for is_loop_prefetching_profitable.
	(is_loop_prefetching_profitable): return false if the estimated prefetch
	count is 0.
---
 gcc/tree-ssa-loop-prefetch.c |   18 +++++++++++++-----
 1 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/gcc/tree-ssa-loop-prefetch.c b/gcc/tree-ssa-loop-prefetch.c
index d63ede1..dd3dabf 100644
--- a/gcc/tree-ssa-loop-prefetch.c
+++ b/gcc/tree-ssa-loop-prefetch.c
@@ -987,18 +987,24 @@ schedule_prefetches (struct mem_ref_group *groups, unsigned unroll_factor,
   return any;
 }
 
-/* Estimate the number of prefetches in the given GROUPS.  */
+/* Estimate the number of prefetches in the given GROUPS.
+   UNROLL_FACTOR is the factor by which LOOP was unrolled.  */
 
 static int
-estimate_prefetch_count (struct mem_ref_group *groups)
+estimate_prefetch_count (struct mem_ref_group *groups, unsigned unroll_factor)
 {
   struct mem_ref *ref;
+  unsigned n_prefetches;
   int prefetch_count = 0;
 
   for (; groups; groups = groups->next)
     for (ref = groups->refs; ref; ref = ref->next)
       if (should_issue_prefetch_p (ref))
-	  prefetch_count++;
+	{
+	  n_prefetches = ((unroll_factor + ref->prefetch_mod - 1)
+			  / ref->prefetch_mod);
+	  prefetch_count += n_prefetches;
+	}
 
   return prefetch_count;
 }
@@ -1620,7 +1626,7 @@ is_loop_prefetching_profitable (unsigned ahead, HOST_WIDE_INT est_niter,
 {
   int insn_to_mem_ratio, insn_to_prefetch_ratio;
 
-  if (mem_ref_count == 0)
+  if (mem_ref_count == 0 || prefetch_count == 0)
     return false;
 
   /* Prefetching improves performance by overlapping cache missing
@@ -1709,7 +1715,7 @@ loop_prefetch_arrays (struct loop *loop)
   /* Step 2: estimate the reuse effects.  */
   prune_by_reuse (refs);
 
-  prefetch_count = estimate_prefetch_count (refs);
+  prefetch_count = estimate_prefetch_count (refs, 1);
   if (prefetch_count == 0)
     goto fail;
 
@@ -1733,6 +1739,8 @@ loop_prefetch_arrays (struct loop *loop)
 	     ahead, unroll_factor, est_niter,
 	     ninsns, mem_ref_count, prefetch_count);
 
+  /* Re-estimate the prefetch count based upon loop unrolling.  */
+  prefetch_count = estimate_prefetch_count (refs, unroll_factor);
   if (!is_loop_prefetching_profitable (ahead, est_niter, ninsns, prefetch_count,
 				       mem_ref_count, unroll_factor))
     goto fail;
-- 
1.6.3.3