From: Connor Abbott <cwabbott0@gmail.com>
Date: Mon, 20 May 2019 12:59:40 +0000 (+0200)
Subject: util/set: Add specialized resizing add function
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=6f9beb28bb55ccf01445c8e57d3dca5216ec530f;p=mesa.git

util/set: Add specialized resizing add function

A significant portion of the time spent in nir_opt_cse for the Dolphin
ubershaders was in resizing the set. When resizing a hash table, we know
in advance that each new element to be inserted will be different from
every other element, so we don't have to compare them, and there will be
no tombstone elements, so we don't have to worry about caching the
first-seen tombstone. We add a specialized add function which skips
these steps entirely, speeding up resizing.

Compile-time results from my shader-db database:

Difference at 95.0% confidence
	-2.29143 +/- 0.845534
	-0.529475% +/- 0.194767%
	(Student's t, pooled s = 1.08807)

Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
---

diff --git a/src/util/set.c b/src/util/set.c
index a1cf05cb4dc..7311f4336e8 100644
--- a/src/util/set.c
+++ b/src/util/set.c
@@ -245,8 +245,26 @@ _mesa_set_search_pre_hashed(const struct set *set, uint32_t hash,
    return set_search(set, hash, key);
 }
 
-static struct set_entry *
-set_add(struct set *ht, uint32_t hash, const void *key);
+static void
+set_add_rehash(struct set *ht, uint32_t hash, const void *key)
+{
+   uint32_t size = ht->size;
+   uint32_t start_address = hash % size;
+   uint32_t double_hash = hash % ht->rehash + 1;
+   uint32_t hash_address = start_address;
+   do {
+      struct set_entry *entry = ht->table + hash_address;
+      if (likely(entry->key == NULL)) {
+         entry->hash = hash;
+         entry->key = key;
+         return;
+      }
+
+      hash_address = hash_address + double_hash;
+      if (hash_address >= size)
+         hash_address -= size;
+   } while (true);
+}
 
 static void
 set_rehash(struct set *ht, unsigned new_size_index)
@@ -273,9 +291,11 @@ set_rehash(struct set *ht, unsigned new_size_index)
    ht->deleted_entries = 0;
 
    set_foreach(&old_ht, entry) {
-      set_add(ht, entry->hash, entry->key);
+      set_add_rehash(ht, entry->hash, entry->key);
    }
 
+   ht->entries = old_ht.entries;
+
    ralloc_free(old_ht.table);
 }