src/compiler/nir/nir_opt_large_constants.c

   1 /*
   2  * Copyright © 2018 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "nir.h"
  25 #include "nir_builder.h"
  26 #include "nir_deref.h"
  27
  28 struct var_info {
  29    bool is_constant;
  30    bool found_read;
  31 };
  32
  33 static nir_ssa_def *
  34 build_constant_load(nir_builder *b, nir_deref_instr *deref,
  35                     glsl_type_size_align_func size_align)
  36 {
  37    nir_variable *var = nir_deref_instr_get_variable(deref);
  38
  39    const unsigned bit_size = glsl_get_bit_size(deref->type);
  40    const unsigned num_components = glsl_get_vector_elements(deref->type);
  41
  42    UNUSED unsigned var_size, var_align;
  43    size_align(var->type, &var_size, &var_align);
  44    assert(var->data.location % var_align == 0);
  45
  46    nir_intrinsic_instr *load =
  47       nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_constant);
  48    load->num_components = num_components;
  49    nir_intrinsic_set_base(load, var->data.location);
  50    nir_intrinsic_set_range(load, var_size);
  51    load->src[0] = nir_src_for_ssa(nir_build_deref_offset(b, deref, size_align));
  52    nir_ssa_dest_init(&load->instr, &load->dest,
  53                      num_components, bit_size, NULL);
  54    nir_builder_instr_insert(b, &load->instr);
  55
  56    if (load->dest.ssa.bit_size < 8) {
  57       /* Booleans are special-cased to be 32-bit
  58        *
  59        * Ideally, for drivers that can handle 32-bit booleans, we wouldn't
  60        * emit the i2b here.  However, at this point, the driver is likely to
  61        * still have 1-bit booleans so we need to at least convert bit sizes.
  62        * Unfortunately, we don't have a good way to annotate the load as
  63        * loading a known boolean value so the optimizer isn't going to be
  64        * able to get rid of the conversion.  Some day, we may solve that
  65        * problem but not today.
  66        */
  67       assert(glsl_type_is_boolean(deref->type));
  68       load->dest.ssa.bit_size = 32;
  69       return nir_i2b(b, &load->dest.ssa);
  70    } else {
  71       return &load->dest.ssa;
  72    }
  73 }
  74
  75 static void
  76 handle_constant_store(nir_builder *b, nir_intrinsic_instr *store,
  77                       glsl_type_size_align_func size_align)
  78 {
  79    nir_deref_instr *deref = nir_src_as_deref(store->src[0]);
  80    assert(!nir_deref_instr_has_indirect(deref));
  81
  82    nir_variable *var = nir_deref_instr_get_variable(deref);
  83
  84    const unsigned bit_size = glsl_get_bit_size(deref->type);
  85    const unsigned num_components = glsl_get_vector_elements(deref->type);
  86
  87    char *dst = (char *)b->shader->constant_data +
  88                var->data.location +
  89                nir_deref_instr_get_const_offset(deref, size_align);
  90
  91    nir_const_value *val = nir_src_as_const_value(store->src[1]);
  92    switch (bit_size) {
  93    case 1:
  94       /* Booleans are special-cased to be 32-bit */
  95       for (unsigned i = 0; i < num_components; i++)
  96          ((int32_t *)dst)[i] = -(int)val->b[i];
  97       break;
  98
  99    case 8:
 100       for (unsigned i = 0; i < num_components; i++)
 101          ((uint8_t *)dst)[i] = val->u8[i];
 102       break;
 103
 104    case 16:
 105       for (unsigned i = 0; i < num_components; i++)
 106          ((uint16_t *)dst)[i] = val->u16[i];
 107       break;
 108
 109    case 32:
 110       for (unsigned i = 0; i < num_components; i++)
 111          ((uint32_t *)dst)[i] = val->u32[i];
 112       break;
 113
 114    case 64:
 115       for (unsigned i = 0; i < num_components; i++)
 116          ((uint64_t *)dst)[i] = val->u64[i];
 117       break;
 118
 119    default:
 120       unreachable("Invalid bit size");
 121    }
 122 }
 123
 124 /** Lower large constant variables to shader constant data
 125  *
 126  * This pass looks for large (type_size(var->type) > threshold) variables
 127  * which are statically constant and moves them into shader constant data.
 128  * This is especially useful when large tables are baked into the shader
 129  * source code because they can be moved into a UBO by the driver to reduce
 130  * register pressure and make indirect access cheaper.
 131  */
 132 bool
 133 nir_opt_large_constants(nir_shader *shader,
 134                         glsl_type_size_align_func size_align,
 135                         unsigned threshold)
 136 {
 137    /* Default to a natural alignment if none is provided */
 138    if (size_align == NULL)
 139       size_align = glsl_get_natural_size_align_bytes;
 140
 141    /* This only works with a single entrypoint */
 142    nir_function_impl *impl = nir_shader_get_entrypoint(shader);
 143
 144    /* This pass can only be run once */
 145    assert(shader->constant_data == NULL && shader->constant_data_size == 0);
 146
 147    /* The index parameter is unused for local variables so we'll use it for
 148     * indexing into our array of variable metadata.
 149     */
 150    unsigned num_locals = 0;
 151    nir_foreach_variable(var, &impl->locals)
 152       var->data.index = num_locals++;
 153
 154    struct var_info *var_infos = malloc(num_locals * sizeof(struct var_info));
 155    for (unsigned i = 0; i < num_locals; i++) {
 156       var_infos[i] = (struct var_info) {
 157          .is_constant = true,
 158          .found_read = false,
 159       };
 160    }
 161
 162    /* First, walk through the shader and figure out what variables we can
 163     * lower to the constant blob.
 164     */
 165    bool first_block = true;
 166    nir_foreach_block(block, impl) {
 167       nir_foreach_instr(instr, block) {
 168          if (instr->type != nir_instr_type_intrinsic)
 169             continue;
 170
 171          nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 172
 173          bool src_is_const = false;
 174          nir_deref_instr *src_deref = NULL, *dst_deref = NULL;
 175          switch (intrin->intrinsic) {
 176          case nir_intrinsic_store_deref:
 177             dst_deref = nir_src_as_deref(intrin->src[0]);
 178             src_is_const = nir_src_is_const(intrin->src[1]);
 179             break;
 180
 181          case nir_intrinsic_load_deref:
 182             src_deref = nir_src_as_deref(intrin->src[0]);
 183             break;
 184
 185          case nir_intrinsic_copy_deref:
 186             /* We always assume the src and therefore the dst are not
 187              * constants here. Copy and constant propagation passes should
 188              * have taken care of this in most cases anyway.
 189              */
 190             dst_deref = nir_src_as_deref(intrin->src[0]);
 191             src_deref = nir_src_as_deref(intrin->src[1]);
 192             src_is_const = false;
 193             break;
 194
 195          default:
 196             continue;
 197          }
 198
 199          if (dst_deref && dst_deref->mode == nir_var_function) {
 200             nir_variable *var = nir_deref_instr_get_variable(dst_deref);
 201             assert(var->data.mode == nir_var_function);
 202
 203             /* We only consider variables constant if they only have constant
 204              * stores, all the stores come before any reads, and all stores
 205              * come in the first block.  We also can't handle indirect stores.
 206              */
 207             struct var_info *info = &var_infos[var->data.index];
 208             if (!src_is_const || info->found_read || !first_block ||
 209                 nir_deref_instr_has_indirect(dst_deref))
 210                info->is_constant = false;
 211          }
 212
 213          if (src_deref && src_deref->mode == nir_var_function) {
 214             nir_variable *var = nir_deref_instr_get_variable(src_deref);
 215             assert(var->data.mode == nir_var_function);
 216
 217             var_infos[var->data.index].found_read = true;
 218          }
 219       }
 220       first_block = false;
 221    }
 222
 223    shader->constant_data_size = 0;
 224    nir_foreach_variable(var, &impl->locals) {
 225       struct var_info *info = &var_infos[var->data.index];
 226       if (!info->is_constant)
 227          continue;
 228
 229       unsigned var_size, var_align;
 230       size_align(var->type, &var_size, &var_align);
 231       if (var_size <= threshold || !info->found_read) {
 232          /* Don't bother lowering small stuff or data that's never read */
 233          info->is_constant = false;
 234          continue;
 235       }
 236
 237       var->data.location = ALIGN_POT(shader->constant_data_size, var_align);
 238       shader->constant_data_size = var->data.location + var_size;
 239    }
 240
 241    if (shader->constant_data_size == 0) {
 242       free(var_infos);
 243       return false;
 244    }
 245
 246    shader->constant_data = rzalloc_size(shader, shader->constant_data_size);
 247
 248    nir_builder b;
 249    nir_builder_init(&b, impl);
 250
 251    nir_foreach_block(block, impl) {
 252       nir_foreach_instr_safe(instr, block) {
 253          if (instr->type != nir_instr_type_intrinsic)
 254             continue;
 255
 256          nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 257
 258          switch (intrin->intrinsic) {
 259          case nir_intrinsic_load_deref: {
 260             nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
 261             if (deref->mode != nir_var_function)
 262                continue;
 263
 264             nir_variable *var = nir_deref_instr_get_variable(deref);
 265             struct var_info *info = &var_infos[var->data.index];
 266             if (info->is_constant) {
 267                b.cursor = nir_after_instr(&intrin->instr);
 268                nir_ssa_def *val = build_constant_load(&b, deref, size_align);
 269                nir_ssa_def_rewrite_uses(&intrin->dest.ssa,
 270                                         nir_src_for_ssa(val));
 271                nir_instr_remove(&intrin->instr);
 272                nir_deref_instr_remove_if_unused(deref);
 273             }
 274             break;
 275          }
 276
 277          case nir_intrinsic_store_deref: {
 278             nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
 279             if (deref->mode != nir_var_function)
 280                continue;
 281
 282             nir_variable *var = nir_deref_instr_get_variable(deref);
 283             struct var_info *info = &var_infos[var->data.index];
 284             if (info->is_constant) {
 285                b.cursor = nir_after_instr(&intrin->instr);
 286                handle_constant_store(&b, intrin, size_align);
 287                nir_instr_remove(&intrin->instr);
 288                nir_deref_instr_remove_if_unused(deref);
 289             }
 290             break;
 291          }
 292
 293          case nir_intrinsic_copy_deref: {
 294             nir_deref_instr *deref = nir_src_as_deref(intrin->src[1]);
 295             if (deref->mode != nir_var_function)
 296                continue;
 297
 298             nir_variable *var = nir_deref_instr_get_variable(deref);
 299             struct var_info *info = &var_infos[var->data.index];
 300             if (info->is_constant) {
 301                b.cursor = nir_after_instr(&intrin->instr);
 302                nir_ssa_def *val = build_constant_load(&b, deref, size_align);
 303                nir_store_deref(&b, nir_src_as_deref(intrin->src[0]), val, ~0);
 304                nir_instr_remove(&intrin->instr);
 305                nir_deref_instr_remove_if_unused(deref);
 306             }
 307             break;
 308          }
 309
 310          default:
 311             continue;
 312          }
 313       }
 314    }
 315
 316    /* Clean up the now unused variables */
 317    nir_foreach_variable_safe(var, &impl->locals) {
 318       if (var_infos[var->data.index].is_constant)
 319          exec_node_remove(&var->node);
 320    }
 321
 322    free(var_infos);
 323
 324    nir_metadata_preserve(impl, nir_metadata_block_index |
 325                                nir_metadata_dominance);
 326    return true;
 327 }