nir: Rewrite lower_clip_cull_distance_arrays to do a lot less lowering

Instead of going to all the work of to combine them into one array, just
make two arrays and use location_frac to colocate them within CLIP0.
Then the back-end can sort things out and stack them on top of each
other.  Thanks to ef99f4c8, we also don't need to set compact anymore.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/nir/nir_lower_clip_cull_distance_arrays.c

@@ -27,10 +27,10 @@
 /**
  * @file
  *
- * This pass combines separate clip and cull distance arrays into a
+ * This pass combines clip and cull distance arrays in separate locations and
- * single array that contains both.  Clip distances come first, then
+ * colocates them both in VARYING_SLOT_CLIP_DIST0.  It does so by maintaining
- * cull distances.  It also populates nir_shader_info with the size
+ * two arrays but making them compact and using location_frac to stack them on
- * of the original arrays so the driver knows which are which.
+ * top of each other.
  */
 
 /**
@@ -56,77 +56,6 @@ get_unwrapped_array_length(nir_shader *nir, nir_variable *var)
    return glsl_get_length(type);
 }
 
-/**
- * Update the type of the combined array (including interface block nesting).
- */
-static void
-update_type(nir_variable *var, gl_shader_stage stage, unsigned length)
-{
-   const struct glsl_type *type = glsl_array_type(glsl_float_type(), length, 0);
-
-   if (nir_is_per_vertex_io(var, stage))
-      type = glsl_array_type(type, glsl_get_length(var->type), 0);
-
-   var->type = type;
-}
-
-static void
-rewrite_clip_cull_deref(nir_builder *b,
-                        nir_deref_instr *deref,
-                        const struct glsl_type *type,
-                        unsigned tail_offset)
-{
-   deref->type = type;
-
-   if (glsl_type_is_array(type)) {
-      const struct glsl_type *child_type = glsl_get_array_element(type);
-      nir_foreach_use(src, &deref->dest.ssa) {
-         rewrite_clip_cull_deref(b, nir_instr_as_deref(src->parent_instr),
-                                 child_type, tail_offset);
-      }
-   } else {
-      assert(glsl_type_is_scalar(type));
-
-      /* This is the end of the line.  Add the tail offset if needed */
-      if (tail_offset > 0) {
-         b->cursor = nir_before_instr(&deref->instr);
-         assert(deref->deref_type == nir_deref_type_array);
-         nir_ssa_def *index = nir_iadd(b, deref->arr.index.ssa,
-                                          nir_imm_int(b, tail_offset));
-         nir_instr_rewrite_src(&deref->instr, &deref->arr.index,
-                               nir_src_for_ssa(index));
-      }
-   }
-}
-
-static void
-rewrite_references(nir_builder *b,
-                   nir_instr *instr,
-                   nir_variable *combined,
-                   unsigned cull_offset)
-{
-   if (instr->type != nir_instr_type_deref)
-      return;
-
-   nir_deref_instr *deref = nir_instr_as_deref(instr);
-   if (deref->deref_type != nir_deref_type_var)
-      return;
-
-   if (deref->var->data.mode != combined->data.mode)
-      return;
-
-   const unsigned location = deref->var->data.location;
-   if (location != VARYING_SLOT_CLIP_DIST0 &&
-       location != VARYING_SLOT_CULL_DIST0)
-      return;
-
-   deref->var = combined;
-   if (location == VARYING_SLOT_CULL_DIST0)
-      rewrite_clip_cull_deref(b, deref, combined->type, cull_offset);
-   else
-      rewrite_clip_cull_deref(b, deref, combined->type, 0);
-}
-
 static bool
 combine_clip_cull(nir_shader *nir,
                   struct exec_list *vars,
@@ -134,7 +63,6 @@ combine_clip_cull(nir_shader *nir,
 {
    nir_variable *cull = NULL;
    nir_variable *clip = NULL;
-   bool progress = false;
 
    nir_foreach_variable(var, vars) {
       if (var->data.location == VARYING_SLOT_CLIP_DIST0)
@@ -144,6 +72,9 @@ combine_clip_cull(nir_shader *nir,
          cull = var;
    }
 
+   if (!cull && !clip)
+      return false;
+
    if (!cull && clip) {
       /* The GLSL IR lowering pass must have converted these to vectors */
       if (!clip->data.compact)
@@ -165,53 +96,28 @@ combine_clip_cull(nir_shader *nir,
    }
 
    if (clip) {
-      clip->data.compact = true;
+      assert(clip->data.compact);
       clip->data.how_declared = nir_var_hidden;
    }
 
    if (cull) {
-      cull->data.compact = true;
+      assert(clip->data.compact);
       cull->data.how_declared = nir_var_hidden;
+      cull->data.location = VARYING_SLOT_CLIP_DIST0 + clip_array_size / 4;
+      cull->data.location_frac = clip_array_size % 4;
    }
 
-   if (cull_array_size > 0) {
+   nir_foreach_function(function, nir) {
-      if (clip_array_size == 0) {
+      if (function->impl) {
-         /* No clip distances, just change the cull distance location */
+         nir_metadata_preserve(function->impl,
-         cull->data.location = VARYING_SLOT_CLIP_DIST0;
+                               nir_metadata_block_index |
-      } else {
+                               nir_metadata_dominance |
-         /* Turn the ClipDistance array into a combined one */
+                               nir_metadata_live_ssa_defs |
-         update_type(clip, nir->info.stage, clip_array_size + cull_array_size);
+                               nir_metadata_loop_analysis);
-
-         /* Rewrite CullDistance to reference the combined array */
-         nir_foreach_function(function, nir) {
-            if (function->impl) {
-               nir_builder b;
-               nir_builder_init(&b, function->impl);
-
-               nir_foreach_block(block, function->impl) {
-                  nir_foreach_instr(instr, block) {
-                     rewrite_references(&b, instr, clip, clip_array_size);
-                  }
-               }
-            }
-         }
-
-         /* Delete the old CullDistance variable */
-         exec_node_remove(&cull->node);
-         ralloc_free(cull);
       }
-
-      nir_foreach_function(function, nir) {
-         if (function->impl) {
-            nir_metadata_preserve(function->impl,
-                                  nir_metadata_block_index |
-                                  nir_metadata_dominance);
-         }
-      }
-      progress = true;
    }
 
-   return progress;
+   return true;
 }
 
 bool