glsl: stop cloning builtin fuctions _mesa_glsl_find_builtin_function()

The cloning was introduced in f81ede4699 to fix a problem with
shaders including IR that was owned by builtins.

However the approach of cloning the whole function each time we
reference a builtin lead to a significant reduction in the GLSL
IR compilers performance.

The previous patch fixes the ownership problem in a more precise
way. So we can now remove this cloning.

Testing on a Ryzen 7 1800X shows a ~15% decreases in compiling the
Deus Ex: Mankind Divided shaders on radeonsi (which take 5min+ on
some machines). Looking just at the GLSL IR compiler the speed up
is ~40%.

Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/compiler/glsl/builtin_functions.cpp

@@ -6291,16 +6291,7 @@ _mesa_glsl_find_builtin_function(_mesa_glsl_parse_state *state,
    s = builtins.find(state, name, actual_parameters);
    mtx_unlock(&builtins_lock);
 
-   if (s == NULL)
-      return NULL;
-
-   struct hash_table *ht =
-      _mesa_hash_table_create(NULL, _mesa_hash_pointer, _mesa_key_pointer_equal);
-   void *mem_ctx = state;
-   ir_function *f = s->function()->clone(mem_ctx, ht);
-   _mesa_hash_table_destroy(ht, NULL);
-
-   return f->matching_signature(state, actual_parameters, true);
+   return s;
 }
 
 bool