glsl: rewrite clip/cull distance lowering pass

The last version of this broke clipping, and I had to spend
sometime getting this working properly.

I had to introduce a third pass to count the clip/cull totals,
all due to one messy corner case. We have a piglit test
tes-input-gl_ClipDistance.shader_test
that doesn't actually output the clip distances, it just passes
them like a varying from TCS->TES, the older lowering pass worked
but to lower clip/cull we need to know the total number of clip+culls
used to defined the new variable correctly, and to offset culls
properly.

This adds an extra pass that works out the sizes for clip/cull,
then lowers gl_ClipDistance then gl_CullDistance into the new
gl_ClipDistanceMESA.

The pass checks using the fixed array sizes code if they array
has been referenced, or is actually never used, and ignores
it in the latter case.

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/compiler/glsl/ir_optimization.h

@@ -119,7 +119,7 @@ bool lower_variable_index_to_cond_assign(gl_shader_stage stage,
     bool lower_temp, bool lower_uniform);
 bool lower_quadop_vector(exec_list *instructions, bool dont_lower_swz);
 bool lower_const_arrays_to_uniforms(exec_list *instructions);
-bool lower_clip_distance(gl_shader *shader);
+bool lower_clip_cull_distance(struct gl_shader_program *prog, gl_shader *shader);
 void lower_output_reads(unsigned stage, exec_list *instructions);
 bool lower_packing_builtins(exec_list *instructions, int op_mask);
 void lower_shared_reference(struct gl_shader *shader, unsigned *shared_size);