From 74746ac03ac75136d5867f0f18fc99fbbede1bf8 Mon Sep 17 00:00:00 2001
From: Caio Oliveira <caio.oliveira@intel.com>
Date: Tue, 25 Jul 2023 13:29:44 -0700
Subject: [PATCH] nir: Add nir_opt_reuse_constants()
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Currently SPIR-V does pull all the NIR constants it creates into the
first block, but we plan to change that behavior to let those constants
be defined as they are used.

This pass was written to provide a fallback to the old behavior, it will
be used for radv to avoid regressions when performing the SPIR-V change.

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5282>
---
 src/compiler/nir/meson.build               |  1 +
 src/compiler/nir/nir.h                     |  2 +
 src/compiler/nir/nir_opt_reuse_constants.c | 49 ++++++++++++++++++++++
 3 files changed, 52 insertions(+)
 create mode 100644 src/compiler/nir/nir_opt_reuse_constants.c

diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build
index 69700ce97e5..1b77eb2d0c4 100644
--- a/src/compiler/nir/meson.build
+++ b/src/compiler/nir/meson.build
@@ -265,6 +265,7 @@ files_libnir = files(
   'nir_opt_reassociate_bfi.c',
   'nir_opt_rematerialize_compares.c',
   'nir_opt_remove_phis.c',
+  'nir_opt_reuse_constants.c',
   'nir_opt_shrink_stores.c',
   'nir_opt_shrink_vectors.c',
   'nir_opt_sink.c',
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index ae036e886c4..627f44b203e 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -6027,6 +6027,8 @@ bool nir_opt_ray_queries(nir_shader *shader);
 
 bool nir_opt_ray_query_ranges(nir_shader *shader);
 
+bool nir_opt_reuse_constants(nir_shader *shader);
+
 void nir_sweep(nir_shader *shader);
 
 void nir_remap_dual_slot_attributes(nir_shader *shader,
diff --git a/src/compiler/nir/nir_opt_reuse_constants.c b/src/compiler/nir/nir_opt_reuse_constants.c
new file mode 100644
index 00000000000..2e559253009
--- /dev/null
+++ b/src/compiler/nir/nir_opt_reuse_constants.c
@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 Intel Corporation
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "nir.h"
+#include "nir_instr_set.h"
+
+bool
+nir_opt_reuse_constants(nir_shader *shader)
+{
+   bool progress = false;
+
+   struct set *consts = nir_instr_set_create(NULL);
+   nir_foreach_function_impl(impl, shader) {
+      _mesa_set_clear(consts, NULL);
+
+      nir_block *start_block = nir_start_block(impl);
+      bool func_progress = false;
+
+      nir_foreach_block_safe(block, impl) {
+         const bool in_start_block = start_block == block;
+         nir_foreach_instr_safe(instr, block) {
+            if (instr->type != nir_instr_type_load_const)
+               continue;
+
+            struct set_entry *entry = _mesa_set_search(consts, instr);
+            if (!entry) {
+               if (!in_start_block)
+                  nir_instr_move(nir_after_block_before_jump(start_block), instr);
+               _mesa_set_add(consts, instr);
+            }
+
+            func_progress |= nir_instr_set_add_or_rewrite(consts, instr, nir_instrs_equal);
+         }
+      }
+
+      if (func_progress) {
+         nir_metadata_preserve(impl, nir_metadata_block_index |
+                                        nir_metadata_dominance);
+         progress = true;
+      } else {
+         nir_metadata_preserve(impl, nir_metadata_all);
+      }
+   }
+
+   nir_instr_set_destroy(consts);
+   return progress;
+}