nir: Add a large constants optimization pass

This pass searches for reasonably large local variables which can be
statically proven to be constant and moves them into shader constant
data.  This is especially useful when large tables are baked into the
shader source code because they can be moved into a UBO by the driver to
reduce register pressure and make indirect access cheaper.

v2 (Jason Ekstrand):
 - Use a size/align function to ensure we get the right alignments
 - Use the newly added deref offset helpers

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/compiler/Makefile.sources

@@ -276,6 +276,7 @@ NIR_FILES = \
 	nir/nir_opt_if.c \
 	nir/nir_opt_intrinsics.c \
 	nir/nir_opt_loop_unroll.c \
+	nir/nir_opt_large_constants.c \
 	nir/nir_opt_move_comparisons.c \
 	nir/nir_opt_move_load_ubo.c \
 	nir/nir_opt_peephole_select.c \

src/compiler/nir/meson.build

@@ -160,6 +160,7 @@ files_libnir = files(
   'nir_opt_global_to_local.c',
   'nir_opt_if.c',
   'nir_opt_intrinsics.c',
+  'nir_opt_large_constants.c',
   'nir_opt_loop_unroll.c',
   'nir_opt_move_comparisons.c',
   'nir_opt_move_load_ubo.c',

src/compiler/nir/nir.h

@@ -2905,6 +2905,10 @@ bool nir_opt_if(nir_shader *shader);
 
 bool nir_opt_intrinsics(nir_shader *shader);
 
+bool nir_opt_large_constants(nir_shader *shader,
+                             glsl_type_size_align_func size_align,
+                             unsigned threshold);
+
 bool nir_opt_loop_unroll(nir_shader *shader, nir_variable_mode indirect_mask);
 
 bool nir_opt_move_comparisons(nir_shader *shader);

src/compiler/nir/nir_opt_large_constants.c

@@ -0,0 +1,305 @@
+/*
+ * Copyright © 2018 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 "nir_deref.h"
+
+struct var_info {
+   bool is_constant;
+   bool found_read;
+};
+
+static nir_ssa_def *
+build_constant_load(nir_builder *b, nir_deref_instr *deref,
+                    glsl_type_size_align_func size_align)
+{
+   nir_variable *var = nir_deref_instr_get_variable(deref);
+
+   const unsigned bit_size = glsl_get_bit_size(deref->type);
+   const unsigned num_components = glsl_get_vector_elements(deref->type);
+
+   UNUSED unsigned var_size, var_align;
+   size_align(var->type, &var_size, &var_align);
+   assert(var->data.location % var_align == 0);
+
+   nir_intrinsic_instr *load =
+      nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_constant);
+   load->num_components = num_components;
+   nir_intrinsic_set_base(load, var->data.location);
+   nir_intrinsic_set_range(load, var_size);
+   load->src[0] = nir_src_for_ssa(nir_build_deref_offset(b, deref, size_align));
+   nir_ssa_dest_init(&load->instr, &load->dest,
+                     num_components, bit_size, NULL);
+   nir_builder_instr_insert(b, &load->instr);
+
+   return &load->dest.ssa;
+}
+
+static void
+handle_constant_store(nir_builder *b, nir_intrinsic_instr *store,
+                      glsl_type_size_align_func size_align)
+{
+   nir_deref_instr *deref = nir_src_as_deref(store->src[0]);
+   assert(!nir_deref_instr_has_indirect(deref));
+
+   nir_variable *var = nir_deref_instr_get_variable(deref);
+
+   const unsigned bit_size = glsl_get_bit_size(deref->type);
+   const unsigned num_components = glsl_get_vector_elements(deref->type);
+
+   char *dst = (char *)b->shader->constant_data +
+               var->data.location +
+               nir_deref_instr_get_const_offset(deref, size_align);
+
+   nir_const_value *val = nir_src_as_const_value(store->src[1]);
+   switch (bit_size) {
+   case 8:
+      for (unsigned i = 0; i < num_components; i++)
+         ((uint8_t *)dst)[i] = val->u8[i];
+      break;
+
+   case 16:
+      for (unsigned i = 0; i < num_components; i++)
+         ((uint16_t *)dst)[i] = val->u16[i];
+      break;
+
+   case 32:
+      for (unsigned i = 0; i < num_components; i++)
+         ((uint32_t *)dst)[i] = val->u32[i];
+      break;
+
+   case 64:
+      for (unsigned i = 0; i < num_components; i++)
+         ((uint64_t *)dst)[i] = val->u64[i];
+      break;
+
+   default:
+      unreachable("Invalid bit size");
+   }
+}
+
+/** Lower large constant variables to shader constant data
+ *
+ * This pass looks for large (type_size(var->type) > threshold) variables
+ * which are statically constant and moves them into shader constant data.
+ * This is especially useful when large tables are baked into the shader
+ * source code because they can be moved into a UBO by the driver to reduce
+ * register pressure and make indirect access cheaper.
+ */
+bool
+nir_opt_large_constants(nir_shader *shader,
+                        glsl_type_size_align_func size_align,
+                        unsigned threshold)
+{
+   /* Default to a natural alignment if none is provided */
+   if (size_align == NULL)
+      size_align = glsl_get_natural_size_align_bytes;
+
+   /* This only works with a single entrypoint */
+   nir_function_impl *impl = nir_shader_get_entrypoint(shader);
+
+   /* This pass can only be run once */
+   assert(shader->constant_data == NULL && shader->constant_data_size == 0);
+
+   /* The index parameter is unused for local variables so we'll use it for
+    * indexing into our array of variable metadata.
+    */
+   unsigned num_locals = 0;
+   nir_foreach_variable(var, &impl->locals)
+      var->data.index = num_locals++;
+
+   struct var_info *var_infos = malloc(num_locals * sizeof(struct var_info));
+   for (unsigned i = 0; i < num_locals; i++) {
+      var_infos[i] = (struct var_info) {
+         .is_constant = true,
+         .found_read = false,
+      };
+   }
+
+   /* First, walk through the shader and figure out what variables we can
+    * lower to the constant blob.
+    */
+   bool first_block = true;
+   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);
+
+         bool src_is_const = false;
+         nir_deref_instr *src_deref = NULL, *dst_deref = NULL;
+         switch (intrin->intrinsic) {
+         case nir_intrinsic_store_deref:
+            dst_deref = nir_src_as_deref(intrin->src[0]);
+            src_is_const = nir_src_as_const_value(intrin->src[1]);
+            break;
+
+         case nir_intrinsic_load_deref:
+            src_deref = nir_src_as_deref(intrin->src[0]);
+            break;
+
+         case nir_intrinsic_copy_deref:
+            /* We always assume the src and therefore the dst are not
+             * constants here. Copy and constant propagation passes should
+             * have taken care of this in most cases anyway.
+             */
+            dst_deref = nir_src_as_deref(intrin->src[0]);
+            src_deref = nir_src_as_deref(intrin->src[1]);
+            src_is_const = false;
+            break;
+
+         default:
+            continue;
+         }
+
+         if (dst_deref && dst_deref->mode == nir_var_local) {
+            nir_variable *var = nir_deref_instr_get_variable(dst_deref);
+            assert(var->data.mode == nir_var_local);
+
+            /* We only consider variables constant if they only have constant
+             * stores, all the stores come before any reads, and all stores
+             * come in the first block.  We also can't handle indirect stores.
+             */
+            struct var_info *info = &var_infos[var->data.index];
+            if (!src_is_const || info->found_read || !first_block ||
+                nir_deref_instr_has_indirect(dst_deref))
+               info->is_constant = false;
+         }
+
+         if (src_deref && src_deref->mode == nir_var_local) {
+            nir_variable *var = nir_deref_instr_get_variable(src_deref);
+            assert(var->data.mode == nir_var_local);
+
+            var_infos[var->data.index].found_read = true;
+         }
+      }
+      first_block = false;
+   }
+
+   shader->constant_data_size = 0;
+   nir_foreach_variable(var, &impl->locals) {
+      struct var_info *info = &var_infos[var->data.index];
+      if (!info->is_constant)
+         continue;
+
+      unsigned var_size, var_align;
+      size_align(var->type, &var_size, &var_align);
+      if (var_size <= threshold || !info->found_read) {
+         /* Don't bother lowering small stuff or data that's never read */
+         info->is_constant = false;
+         continue;
+      }
+
+      var->data.location = ALIGN_POT(shader->constant_data_size, var_align);
+      shader->constant_data_size = var->data.location + var_size;
+   }
+
+   if (shader->constant_data_size == 0) {
+      free(var_infos);
+      return false;
+   }
+
+   shader->constant_data = rzalloc_size(shader, shader->constant_data_size);
+
+   nir_builder b;
+   nir_builder_init(&b, impl);
+
+   nir_foreach_block(block, impl) {
+      nir_foreach_instr_safe(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_load_deref: {
+            nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
+            if (deref->mode != nir_var_local)
+               continue;
+
+            nir_variable *var = nir_deref_instr_get_variable(deref);
+            struct var_info *info = &var_infos[var->data.index];
+            if (info->is_constant) {
+               b.cursor = nir_after_instr(&intrin->instr);
+               nir_ssa_def *val = build_constant_load(&b, deref, size_align);
+               nir_ssa_def_rewrite_uses(&intrin->dest.ssa,
+                                        nir_src_for_ssa(val));
+               nir_instr_remove(&intrin->instr);
+               nir_deref_instr_remove_if_unused(deref);
+            }
+            break;
+         }
+
+         case nir_intrinsic_store_deref: {
+            nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
+            if (deref->mode != nir_var_local)
+               continue;
+
+            nir_variable *var = nir_deref_instr_get_variable(deref);
+            struct var_info *info = &var_infos[var->data.index];
+            if (info->is_constant) {
+               b.cursor = nir_after_instr(&intrin->instr);
+               handle_constant_store(&b, intrin, size_align);
+               nir_instr_remove(&intrin->instr);
+               nir_deref_instr_remove_if_unused(deref);
+            }
+            break;
+         }
+
+         case nir_intrinsic_copy_deref: {
+            nir_deref_instr *deref = nir_src_as_deref(intrin->src[1]);
+            if (deref->mode != nir_var_local)
+               continue;
+
+            nir_variable *var = nir_deref_instr_get_variable(deref);
+            struct var_info *info = &var_infos[var->data.index];
+            if (info->is_constant) {
+               b.cursor = nir_after_instr(&intrin->instr);
+               nir_ssa_def *val = build_constant_load(&b, deref, size_align);
+               nir_store_deref(&b, nir_src_as_deref(intrin->src[0]), val, ~0);
+               nir_instr_remove(&intrin->instr);
+               nir_deref_instr_remove_if_unused(deref);
+            }
+            break;
+         }
+
+         default:
+            continue;
+         }
+      }
+   }
+
+   /* Clean up the now unused variables */
+   nir_foreach_variable_safe(var, &impl->locals) {
+      if (var_infos[var->data.index].is_constant)
+         exec_node_remove(&var->node);
+   }
+
+   free(var_infos);
+
+   nir_metadata_preserve(impl, nir_metadata_block_index |
+                               nir_metadata_dominance);
+   return true;
+}