Mesa (master): util/set: optimize rehash for empty table and no-func clears

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Module: Mesa
Branch: master
Commit: 5f3f128088ae45734723071ec4af340488ece741
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=5f3f128088ae45734723071ec4af340488ece741

Author: Mike Blumenkrantz <michael.blumenkrantz at gmail.com>
Date:   Tue Jan 12 12:20:41 2021 -0500

util/set: optimize rehash for empty table and no-func clears

if the table is filled with deleted entries, we don't need to rzalloc+free an identical
block of memory for the table, we can just memset the existing one

the same applies to table clears without a function passed in that the table
doesn't need to be iterated and can just be memset

Reviewed-by: Eric Anholt <eric at anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8450>

---

 src/util/set.c                  | 32 ++++++++++++++++++++++++--------
 src/util/tests/set/set_test.cpp |  7 +++++++
 2 files changed, 31 insertions(+), 8 deletions(-)

diff --git a/src/util/set.c b/src/util/set.c
index f10694537c1..f071aca24fe 100644
--- a/src/util/set.c
+++ b/src/util/set.c
@@ -211,6 +211,14 @@ _mesa_set_destroy(struct set *ht, void (*delete_function)(struct set_entry *entr
    ralloc_free(ht);
 }
 
+
+static void
+set_clear_fast(struct set *ht)
+{
+   memset(ht->table, 0, sizeof(struct set_entry) * hash_sizes[ht->size_index].size);
+   ht->entries = ht->deleted_entries = 0;
+}
+
 /**
  * Clears all values from the given set.
  *
@@ -225,15 +233,17 @@ _mesa_set_clear(struct set *set, void (*delete_function)(struct set_entry *entry
 
    struct set_entry *entry;
 
-   for (entry = set->table; entry != set->table + set->size; entry++) {
-      if (entry_is_present(entry) && delete_function != NULL)
-         delete_function(entry);
-
-      entry->key = NULL;
-   }
+   if (delete_function) {
+      for (entry = set->table; entry != set->table + set->size; entry++) {
+         if (entry_is_present(entry))
+            delete_function(entry);
 
-   set->entries = 0;
-   set->deleted_entries = 0;
+         entry->key = NULL;
+      }
+      set->entries = 0;
+      set->deleted_entries = 0;
+   } else
+      set_clear_fast(set);
 }
 
 /**
@@ -314,6 +324,12 @@ set_rehash(struct set *ht, unsigned new_size_index)
    struct set old_ht;
    struct set_entry *table;
 
+   if (ht->size_index == new_size_index && ht->deleted_entries == ht->max_entries) {
+      set_clear_fast(ht);
+      assert(!ht->entries);
+      return;
+   }
+
    if (new_size_index >= ARRAY_SIZE(hash_sizes))
       return;
 
diff --git a/src/util/tests/set/set_test.cpp b/src/util/tests/set/set_test.cpp
index 0b4355af128..6eda08de698 100644
--- a/src/util/tests/set/set_test.cpp
+++ b/src/util/tests/set/set_test.cpp
@@ -51,6 +51,13 @@ TEST(set, basic)
    entry = _mesa_set_search(s, a);
    EXPECT_FALSE(entry);
 
+   _mesa_set_clear(s, NULL);
+   EXPECT_EQ(s->entries, 0);
+   EXPECT_EQ(s->deleted_entries, 0);
+   set_foreach(s, he) {
+      GTEST_FAIL();
+   }
+
    _mesa_set_destroy(s, NULL);
 }