nir: add a ray query optimization pass

Just remove queries that are never used or proceeded with. The latter
case leading to undefined values.

v2: Don't use nir_shader_instructions_pass() to find variables (Caio)
    Simplify replacement (Caio)

v3: Don't track all the queries intrinsic effects (Caio)
    Rename things to represent only read queries (Caio)
    Use set instead of hash_table (Caio)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13718>

src/compiler/nir/meson.build

@@ -240,6 +240,7 @@ files_libnir = files(
   'nir_opt_offsets.c',
   'nir_opt_peephole_select.c',
   'nir_opt_phi_precision.c',
+  'nir_opt_ray_queries.c',
   'nir_opt_rematerialize_compares.c',
   'nir_opt_remove_phis.c',
   'nir_opt_shrink_vectors.c',

src/compiler/nir/nir.h

@@ -5258,6 +5258,8 @@ bool nir_opt_vectorize(nir_shader *shader, nir_opt_vectorize_cb filter,
 bool nir_opt_conditional_discard(nir_shader *shader);
 bool nir_opt_move_discards_to_top(nir_shader *shader);
 
+bool nir_opt_ray_queries(nir_shader *shader);
+
 typedef bool (*nir_should_vectorize_mem_func)(unsigned align_mul,
                                               unsigned align_offset,
                                               unsigned bit_size,

src/compiler/nir/nir_opt_ray_queries.c

@@ -0,0 +1,155 @@
+/*
+ * Copyright © 2021 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+
+#include "nir.h"
+#include "nir_builder.h"
+
+#include "util/set.h"
+#include "util/macros.h"
+
+/** @file nir_opt_ray_queries.c
+ *
+ * Remove ray queries that the shader is not using the result of.
+ */
+
+static void
+mark_query_read(struct set *queries,
+                nir_intrinsic_instr *intrin)
+{
+   nir_ssa_def *rq_def = intrin->src[0].ssa;
+
+   nir_variable *query;
+   if (rq_def->parent_instr->type == nir_instr_type_intrinsic) {
+      nir_intrinsic_instr *load_deref =
+         nir_instr_as_intrinsic(rq_def->parent_instr);
+      assert(load_deref->intrinsic == nir_intrinsic_load_deref);
+
+      query = nir_intrinsic_get_var(load_deref, 0);
+   } else if (rq_def->parent_instr->type == nir_instr_type_deref) {
+      query = nir_deref_instr_get_variable(
+         nir_instr_as_deref(rq_def->parent_instr));
+   } else {
+      return;
+   }
+   assert(query);
+
+   _mesa_set_add(queries, query);
+}
+
+static void
+nir_find_ray_queries_read(struct set *queries,
+                          nir_shader *shader)
+{
+   nir_foreach_function(function, shader) {
+      nir_function_impl *impl = function->impl;
+
+      if (!impl)
+         continue;
+
+      nir_foreach_block(block, impl) {
+         nir_foreach_instr(instr, block) {
+            if (instr->type != nir_instr_type_intrinsic)
+               continue;
+
+            nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+            switch (intrin->intrinsic) {
+            case nir_intrinsic_rq_proceed:
+               if (list_length(&intrin->dest.ssa.uses) > 0 ||
+                   list_length(&intrin->dest.ssa.if_uses) > 0)
+                  mark_query_read(queries, intrin);
+               break;
+            case nir_intrinsic_rq_load:
+               mark_query_read(queries, intrin);
+               break;
+            default:
+               break;
+            }
+         }
+      }
+   }
+}
+
+static bool
+nir_replace_unread_queries_instr(nir_builder *b, nir_instr *instr, void *data)
+{
+   struct set *queries = data;
+
+   if (instr->type != nir_instr_type_intrinsic)
+      return false;
+
+   nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+   switch (intrin->intrinsic) {
+   case nir_intrinsic_rq_initialize:
+   case nir_intrinsic_rq_terminate:
+   case nir_intrinsic_rq_generate_intersection:
+   case nir_intrinsic_rq_confirm_intersection:
+      break;
+   case nir_intrinsic_rq_proceed:
+      break;
+   default:
+      return false;
+   }
+
+   nir_variable *query = nir_intrinsic_get_var(intrin, 0);
+   assert(query);
+
+   struct set_entry *entry = _mesa_set_search(queries, query);
+   if (entry)
+      return false;
+
+   if (intrin->intrinsic == nir_intrinsic_rq_load) {
+      assert(list_is_empty(&intrin->dest.ssa.uses));
+      assert(list_is_empty(&intrin->dest.ssa.if_uses));
+   }
+
+   nir_instr_remove(instr);
+
+   return true;
+}
+
+bool
+nir_opt_ray_queries(nir_shader *shader)
+{
+   struct set *read_queries = _mesa_pointer_set_create(NULL);
+   nir_find_ray_queries_read(read_queries, shader);
+
+   bool progress =
+      nir_shader_instructions_pass(shader,
+                                   nir_replace_unread_queries_instr,
+                                   nir_metadata_block_index |
+                                   nir_metadata_dominance,
+                                   read_queries);
+
+   /* Update the number of queries if some have been removed. */
+   if (progress) {
+      nir_remove_dead_derefs(shader);
+      nir_remove_dead_variables(shader,
+                                nir_var_shader_temp | nir_var_function_temp,
+                                NULL);
+      nir_shader_gather_info(shader, nir_shader_get_entrypoint(shader));
+   }
+
+   _mesa_set_destroy(read_queries, NULL);
+
+   return progress;
+}