gallium: avoid redundant tgsi_exec_machine_bind_shader() calls on draw exec path

tgsi_exec_machine_bind_shader() isn't cheap so avoiding unecessary calls
is a big win.
A similar change should be done for softpipe's fragment exec path but
extra care needs to be taken with the texture sampler state/params.

diff --git a/src/gallium/auxiliary/draw/draw_vs_exec.c b/src/gallium/auxiliary/draw/draw_vs_exec.c
index 4456380..8041705 100644 (file)
--- a/src/gallium/auxiliary/draw/draw_vs_exec.c
+++ b/src/gallium/auxiliary/draw/draw_vs_exec.c
@@ -46,6 +46,7 @@
 struct exec_vertex_shader {
    struct draw_vertex_shader base;
    struct tgsi_exec_machine *machine;
+   struct tgsi_token *machine_tokens;
 };
 
 static struct exec_vertex_shader *exec_vertex_shader( struct draw_vertex_shader *vs )
@@ -62,12 +63,16 @@ vs_exec_prepare( struct draw_vertex_shader *shader,
 {
    struct exec_vertex_shader *evs = exec_vertex_shader(shader);
 
-   /* specify the vertex program to interpret/execute */
-   tgsi_exec_machine_bind_shader(evs->machine,
-                                shader->state.tokens,
-                                PIPE_MAX_SAMPLERS,
-                                NULL /*samplers*/ );
-
+   /* Specify the vertex program to interpret/execute.
+    * Avoid rebinding when possible.
+    */
+   if (evs->machine_tokens != shader->state.tokens) {
+      tgsi_exec_machine_bind_shader(evs->machine,
+                                    shader->state.tokens,
+                                    PIPE_MAX_SAMPLERS,
+                                    NULL /*samplers*/ );
+      evs->machine_tokens = shader->state.tokens;
+   }
 }