[PATCH 2/2] IPA ICF: use fibonacci heap instead of list as a worklist.

[Martin Liška]

This is second part which has not a significant speed up but
it's mentioned in the Value Numbering algorithm as a useful heuristics.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

gcc/ChangeLog:

2019-06-03  Martin Liska  <mli...@suse.cz>

        * ipa-icf.c (sem_item_optimizer::add_item_to_class): Count
        number of references.
        (sem_item_optimizer::do_congruence_step):
        (sem_item_optimizer::worklist_push): Dump how references
        a class has.
        (sem_item_optimizer::worklist_pop): Use heap.
        (sem_item_optimizer::process_cong_reduction): Likewise.
        * ipa-icf.h: Use fibonacci_heap insteam of std::list.
---
 gcc/ipa-icf.c | 12 +++++++-----
 gcc/ipa-icf.h |  8 ++++++--
 2 files changed, 13 insertions(+), 7 deletions(-)



diff --git a/gcc/ipa-icf.c b/gcc/ipa-icf.c
index a4705eee936..ac563623ea2 100644
--- a/gcc/ipa-icf.c
+++ b/gcc/ipa-icf.c
@@ -80,6 +80,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "print-tree.h"
 #include "ipa-utils.h"
 #include "ipa-icf-gimple.h"
+#include "fibonacci_heap.h"
 #include "ipa-icf.h"
 #include "stor-layout.h"
 #include "dbgcnt.h"
@@ -2626,6 +2627,7 @@ sem_item_optimizer::add_item_to_class (congruence_class *cls, sem_item *item)
 {
   item->index_in_class = cls->members.length ();
   cls->members.safe_push (item);
+  cls->referenced_by_count += item->referenced_by_count;
   item->cls = cls;
 }
 
@@ -3188,7 +3190,8 @@ sem_item_optimizer::do_congruence_step (congruence_class *cls)
   {
     if (dump_file && (dump_flags & TDF_DETAILS))
       fprintf (dump_file, "  processing congruence step for class: %u "
-	       "(%u items), index: %u\n", cls->id, cls->members.length (), i);
+	       "(%u items, %u references), index: %u\n", cls->id,
+	       cls->referenced_by_count, cls->members.length (), i);
     do_congruence_step_for_index (cls, i);
 
     if (splitter_class_removed)
@@ -3208,7 +3211,7 @@ sem_item_optimizer::worklist_push (congruence_class *cls)
     return;
 
   cls->in_worklist = true;
-  worklist.push_back (cls);
+  worklist.insert (cls->referenced_by_count, cls);
 }
 
 /* Pops a class from worklist. */
@@ -3220,8 +3223,7 @@ sem_item_optimizer::worklist_pop (void)
 
   while (!worklist.empty ())
     {
-      cls = worklist.front ();
-      worklist.pop_front ();
+      cls = worklist.extract_min ();
       if (cls->in_worklist)
 	{
 	  cls->in_worklist = false;
@@ -3253,7 +3255,7 @@ sem_item_optimizer::process_cong_reduction (void)
 
   if (dump_file)
     fprintf (dump_file, "Worklist has been filled with: %lu\n",
-	     (unsigned long) worklist.size ());
+	     (unsigned long) worklist.nodes ());
 
   if (dump_file && (dump_flags & TDF_DETAILS))
     fprintf (dump_file, "Congruence class reduction\n");
diff --git a/gcc/ipa-icf.h b/gcc/ipa-icf.h
index ede4c94dbd3..6b81eb38b2a 100644
--- a/gcc/ipa-icf.h
+++ b/gcc/ipa-icf.h
@@ -29,7 +29,8 @@ class congruence_class
 {
 public:
   /* Congruence class constructor for a new class with _ID.  */
-  congruence_class (unsigned int _id): in_worklist (false), id(_id)
+  congruence_class (unsigned int _id): in_worklist (false), id (_id),
+  referenced_by_count (0)
   {
   }
 
@@ -54,6 +55,9 @@ public:
 
   /* Global unique class identifier.  */
   unsigned int id;
+
+  /* Total number of references to items of this class.  */
+  unsigned referenced_by_count;
 };
 
 /* Semantic item type enum.  */
@@ -530,7 +534,7 @@ public:
 
   /* Worklist of congruence classes that can potentially
      refine classes of congruence.  */
-  std::list<congruence_class *> worklist;
+  fibonacci_heap<unsigned, congruence_class> worklist;
 
   /* Remove semantic ITEM and release memory.  */
   void remove_item (sem_item *item);