From d63a36ef3a4dd9cef1273fac5949e587c42813b5 Mon Sep 17 00:00:00 2001
From: Keith Whitwell <keith@tungstengraphics.com>
Date: Fri, 3 Oct 2008 16:46:48 +0100
Subject: [PATCH] Mesa: short-circuit case when looking up the same program
 twice in cache

---
 src/mesa/shader/prog_cache.c | 29 +++++++++++++++++++++--------
 src/mesa/shader/prog_cache.h |  2 +-
 2 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/src/mesa/shader/prog_cache.c b/src/mesa/shader/prog_cache.c
index 36a25377c55..9437e596138 100644
--- a/src/mesa/shader/prog_cache.c
+++ b/src/mesa/shader/prog_cache.c
@@ -44,6 +44,7 @@ struct cache_item
 struct gl_program_cache
 {
    struct cache_item **items;
+   struct cache_item *last;
    GLuint size, n_items;
 };
 
@@ -83,6 +84,8 @@ rehash(struct gl_program_cache *cache)
    struct cache_item *c, *next;
    GLuint size, i;
 
+   cache->last = NULL;
+
    size = cache->size * 3;
    items = (struct cache_item**) _mesa_malloc(size * sizeof(*items));
    _mesa_memset(items, 0, size * sizeof(*items));
@@ -105,6 +108,8 @@ clear_cache(GLcontext *ctx, struct gl_program_cache *cache)
 {
    struct cache_item *c, *next;
    GLuint i;
+   
+   cache->last = NULL;
 
    for (i = 0; i < cache->size; i++) {
       for (c = cache->items[i]; c; c = next) {
@@ -149,18 +154,26 @@ _mesa_delete_program_cache(GLcontext *ctx, struct gl_program_cache *cache)
 
 
 struct gl_program *
-_mesa_search_program_cache(const struct gl_program_cache *cache,
+_mesa_search_program_cache(struct gl_program_cache *cache,
                            const void *key, GLuint keysize)
 {
-   const GLuint hash = hash_key(key, keysize);
-   struct cache_item *c;
-
-   for (c = cache->items[hash % cache->size]; c; c = c->next) {
-      if (c->hash == hash && memcmp(c->key, key, keysize) == 0)
-	 return c->program;
+   if (cache->last && 
+       memcmp(cache->last->key, key, keysize) == 0) {
+      return cache->last->program;
    }
+   else {
+      const GLuint hash = hash_key(key, keysize);
+      struct cache_item *c;
+
+      for (c = cache->items[hash % cache->size]; c; c = c->next) {
+         if (c->hash == hash && memcmp(c->key, key, keysize) == 0) {
+            cache->last = c;
+            return c->program;
+         }
+      }
 
-   return NULL;
+      return NULL;
+   }
 }
 
 
diff --git a/src/mesa/shader/prog_cache.h b/src/mesa/shader/prog_cache.h
index a8c91fba011..4e1ccac03ff 100644
--- a/src/mesa/shader/prog_cache.h
+++ b/src/mesa/shader/prog_cache.h
@@ -42,7 +42,7 @@ _mesa_delete_program_cache(GLcontext *ctx, struct gl_program_cache *pc);
 
 
 extern struct gl_program *
-_mesa_search_program_cache(const struct gl_program_cache *cache,
+_mesa_search_program_cache(struct gl_program_cache *cache,
                            const void *key, GLuint keysize);
 
 extern void
-- 
2.30.2