Re: [PATCH] Speed up qsort in IPA ICF

[Martin Liška <mliska at suse dot cz>]

On 9/19/19 1:01 PM, Richard Biener wrote:
> On Thu, Sep 19, 2019 at 11:06 AM Martin Liška <mliska@suse.cz> wrote:
>>
>> Hi.
>>
>> As Alexander pointed out, the sort_congruence_class_groups_by_decl_uid is the most
>> expensive qsort operator in tramp3d compilation. It does unfortunate 7 pointer dereferences
>> via: DECL_UID (classes[i]->classes[0]->members[0]->decl). I'm suggesting to cache that
>> in congruence_class_group.
>>
>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>>
>> Ready to be installed?
> 
> Since we're populating the classes vector right before you could elide
> the new field and do it in the same iteration by having
> 
> auto_vec <std::pair<congruence_class_group *, unsigned> > classes
> 
> and pushing *it, DECL_UID and then sorting by the readily available
> UID in the data?  That makes the sort use a linear memory region
> w/o dereferences.

Good point, there's a tested patch.

Martin

> 
> Richard.
> 
>> Thanks,
>> Martin
>>
>> gcc/ChangeLog:
>>
>> 2019-09-19  Martin Liska  <mliska@suse.cz>
>>
>>         * ipa-icf.c (sort_sem_items_by_decl_uid): Simplify comparator.
>>         (sort_congruence_classes_by_decl_uid): Likewise.
>>         (sort_congruence_class_groups_by_decl_uid): Use
>>         congruence_class_group::uid.
>>         (sem_item_optimizer::merge_classes): Cache
>>         DECL_UID (classes[i]->classes[0]->members[0]->decl).
>>         * ipa-icf.h (struct congruence_class_group): New field.
>> ---
>>  gcc/ipa-icf.c | 29 +++++------------------------
>>  gcc/ipa-icf.h |  1 +
>>  2 files changed, 6 insertions(+), 24 deletions(-)
>>
>>

>From 05a78667e932e554dfbd69433ad66242cbca6492 Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Thu, 19 Sep 2019 09:41:39 +0200
Subject: [PATCH] Speed up qsort in IPA ICF.

gcc/ChangeLog:

2019-09-19  Martin Liska  <mliska@suse.cz>

	* ipa-icf.c (sort_sem_items_by_decl_uid): Simplify comparator.
	(sort_congruence_classes_by_decl_uid): Likewise.
	(sort_congruence_class_groups_by_decl_uid): Use std::pair for
	easier sorting.
	(sem_item_optimizer::merge_classes): Likewise.
---
 gcc/ipa-icf.c | 49 ++++++++++++++++---------------------------------
 1 file changed, 16 insertions(+), 33 deletions(-)

diff --git a/gcc/ipa-icf.c b/gcc/ipa-icf.c
index c9c3cb4a331..59b7f8b1b9d 100644
--- a/gcc/ipa-icf.c
+++ b/gcc/ipa-icf.c
@@ -3350,13 +3350,7 @@ sort_sem_items_by_decl_uid (const void *a, const void *b)
 
   int uid1 = DECL_UID (i1->decl);
   int uid2 = DECL_UID (i2->decl);
-
-  if (uid1 < uid2)
-    return -1;
-  else if (uid1 > uid2)
-    return 1;
-  else
-    return 0;
+  return uid1 - uid2;
 }
 
 /* Sort pair of congruence_classes A and B by DECL_UID of the first member.  */
@@ -3369,13 +3363,7 @@ sort_congruence_classes_by_decl_uid (const void *a, const void *b)
 
   int uid1 = DECL_UID (c1->members[0]->decl);
   int uid2 = DECL_UID (c2->members[0]->decl);
-
-  if (uid1 < uid2)
-    return -1;
-  else if (uid1 > uid2)
-    return 1;
-  else
-    return 0;
+  return uid1 - uid2;
 }
 
 /* Sort pair of congruence_class_groups A and B by
@@ -3384,20 +3372,11 @@ sort_congruence_classes_by_decl_uid (const void *a, const void *b)
 static int
 sort_congruence_class_groups_by_decl_uid (const void *a, const void *b)
 {
-  const congruence_class_group *g1
-    = *(const congruence_class_group * const *)a;
-  const congruence_class_group *g2
-    = *(const congruence_class_group * const *)b;
-
-  int uid1 = DECL_UID (g1->classes[0]->members[0]->decl);
-  int uid2 = DECL_UID (g2->classes[0]->members[0]->decl);
-
-  if (uid1 < uid2)
-    return -1;
-  else if (uid1 > uid2)
-    return 1;
-  else
-    return 0;
+  const std::pair<congruence_class_group *, int> *g1
+    = *(const std::pair<congruence_class_group *, int> *const *) a;
+  const std::pair<congruence_class_group *, int> *g2
+    = *(const std::pair<congruence_class_group *, int> *const *) b;
+  return g1->second - g2->second;
 }
 
 /* After reduction is done, we can declare all items in a group
@@ -3445,10 +3424,14 @@ sem_item_optimizer::merge_classes (unsigned int prev_class_count)
 	  }
       }
 
-  auto_vec <congruence_class_group *> classes (m_classes.elements ());
+  auto_vec<std::pair<congruence_class_group *, int> > classes (
+    m_classes.elements ());
   for (hash_table<congruence_class_hash>::iterator it = m_classes.begin ();
        it != m_classes.end (); ++it)
-    classes.quick_push (*it);
+    {
+      int uid = DECL_UID ((*it)->classes[0]->members[0]->decl);
+      classes.quick_push (std::pair<congruence_class_group *, int> (*it, uid));
+    }
 
   classes.qsort (sort_congruence_class_groups_by_decl_uid);
 
@@ -3470,11 +3453,11 @@ sem_item_optimizer::merge_classes (unsigned int prev_class_count)
     }
 
   unsigned int l;
-  congruence_class_group *it;
+  std::pair<congruence_class_group *, int> *it;
   FOR_EACH_VEC_ELT (classes, l, it)
-    for (unsigned int i = 0; i < it->classes.length (); i++)
+    for (unsigned int i = 0; i < it->first->classes.length (); i++)
       {
-	congruence_class *c = it->classes[i];
+	congruence_class *c = it->first->classes[i];
 
 	if (c->members.length () == 1)
 	  continue;
-- 
2.23.0