i965/gen6+: Remove VUE map dependency on userclip_active.

Previously, on Gen6+, we laid out the vertex (or geometry) shader VUE
map differently depending whether user clipping was active.  If it was
active, we put the clip distances in slots 2 and 3 (where the clipper
expects them); if it was inactive, we assigned them in the order of
the gl_varying_slot enum.

This made for unnecessary recompiles, since turning clipping on/off
for a shader that used gl_ClipDistance might rearrange the varyings.
It also required extra bookkeeping, since it required the user
clipping flag to be provided to brw_compute_vue_map() as a parameter.

With this patch, we always put clip distances at in slots 2 and 3 if
they are written to.  do_vs_prog() and do_gs_prog() are responsible
for ensuring that clip distances are written to when user clipping is
enabled (as do_vs_prog() previously did for gen4-5).

This makes the only input to brw_compute_vue_map() a bitfield of which
varyings the shader writes to, a fact that we'll take advantage of in
forthcoming patches.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/i965/brw_context.h

@@ -436,7 +436,7 @@ static inline GLuint brw_varying_to_offset(struct brw_vue_map *vue_map,
 }
 
 void brw_compute_vue_map(struct brw_context *brw, struct brw_vue_map *vue_map,
-                         GLbitfield64 slots_valid, bool userclip_active);
+                         GLbitfield64 slots_valid);
 
 
 /**

src/mesa/drivers/dri/i965/brw_vec4_gs.c

@@ -94,9 +94,18 @@ do_gs_prog(struct brw_context *brw,
    c.prog_data.control_data_header_size_hwords =
       ALIGN(c.control_data_header_size_bits, 256) / 256;
 
-   brw_compute_vue_map(brw, &c.prog_data.base.vue_map,
-                       gp->program.Base.OutputsWritten,
-                       c.key.base.userclip_active);
+   GLbitfield64 outputs_written = gp->program.Base.OutputsWritten;
+
+   /* In order for legacy clipping to work, we need to populate the clip
+    * distance varying slots whenever clipping is enabled, even if the vertex
+    * shader doesn't write to gl_ClipDistance.
+    */
+   if (c.key.base.userclip_active) {
+      outputs_written |= BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST0);
+      outputs_written |= BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST1);
+   }
+
+   brw_compute_vue_map(brw, &c.prog_data.base.vue_map, outputs_written);
 
    /* Compute the output vertex size.
     *

src/mesa/drivers/dri/i965/brw_vs.c

@@ -52,14 +52,10 @@ static inline void assign_vue_slot(struct brw_vue_map *vue_map,
 
 /**
  * Compute the VUE map for vertex shader program.
- *
- * Note that consumers of this map using cache keys must include
- * prog_data->userclip and prog_data->outputs_written in their key
- * (generated by CACHE_NEW_VS_PROG).
  */
 void
 brw_compute_vue_map(struct brw_context *brw, struct brw_vue_map *vue_map,
-                    GLbitfield64 slots_valid, bool userclip_active)
+                    GLbitfield64 slots_valid)
 {
    vue_map->slots_valid = slots_valid;
    int i;
@@ -112,10 +108,11 @@ brw_compute_vue_map(struct brw_context *brw, struct brw_vue_map *vue_map,
        */
       assign_vue_slot(vue_map, VARYING_SLOT_PSIZ);
       assign_vue_slot(vue_map, VARYING_SLOT_POS);
-      if (userclip_active) {
+      if (slots_valid & BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST0))
          assign_vue_slot(vue_map, VARYING_SLOT_CLIP_DIST0);
+      if (slots_valid & BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST1))
          assign_vue_slot(vue_map, VARYING_SLOT_CLIP_DIST1);
-      }
+
       /* front and back colors need to be consecutive so that we can use
        * ATTRIBUTE_SWIZZLE_INPUTATTR_FACING to swizzle them when doing
        * two-sided color.
@@ -272,15 +269,18 @@ do_vs_prog(struct brw_context *brw,
          outputs_written |= BITFIELD64_BIT(VARYING_SLOT_COL0);
       if (outputs_written & BITFIELD64_BIT(VARYING_SLOT_BFC1))
          outputs_written |= BITFIELD64_BIT(VARYING_SLOT_COL1);
-
-      if (c.key.base.userclip_active) {
-         outputs_written |= BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST0);
-         outputs_written |= BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST1);
-      }
    }
 
-   brw_compute_vue_map(brw, &prog_data.base.vue_map, outputs_written,
-                       c.key.base.userclip_active);
+   /* In order for legacy clipping to work, we need to populate the clip
+    * distance varying slots whenever clipping is enabled, even if the vertex
+    * shader doesn't write to gl_ClipDistance.
+    */
+   if (c.key.base.userclip_active) {
+      outputs_written |= BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST0);
+      outputs_written |= BITFIELD64_BIT(VARYING_SLOT_CLIP_DIST1);
+   }
+
+   brw_compute_vue_map(brw, &prog_data.base.vue_map, outputs_written);
 
    if (0) {
       _mesa_fprint_program_opt(stdout, &c.vp->program.Base, PROG_PRINT_DEBUG,