glsl: Defer initialization of built-in functions until they're needed.

Very simple shaders don't actually use GLSL built-ins.  For example:
- gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
- gl_FragColor = vec4(0.0);
Both of the shaders used by _mesa_meta_glsl_Clear() also qualify.

By waiting to initialize the built-ins until the first time we need to
look for a signature, we can avoid the overhead entirely in these cases.

Makes piglit run roughly 18% faster (255 vs. 312 seconds).

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Eric Anholt <[email protected]>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/glsl/builtins/tools/generate_builtins.py b/src/glsl/builtins/tools/generate_builtins.py
index 17d528c2180..8ce2b70c500 100755
--- a/src/glsl/builtins/tools/generate_builtins.py
+++ b/src/glsl/builtins/tools/generate_builtins.py
@@ -228,12 +228,14 @@ _mesa_read_profile(struct _mesa_glsl_parse_state *state,
 void
 _mesa_glsl_initialize_functions(struct _mesa_glsl_parse_state *state)
 {
+   /* If we've already initialized the built-ins, bail early. */
+   if (state->num_builtins_to_link > 0)
+      return;
+
    if (builtin_mem_ctx == NULL) {
       builtin_mem_ctx = ralloc_context(NULL); // "GLSL built-in functions"
       memset(&builtin_profiles, 0, sizeof(builtin_profiles));
    }
-
-   state->num_builtins_to_link = 0;
 """
 
     i = 0