src/compiler/nir/nir_remove_dead_variables.c

   1 /*
   2  * Copyright © 2014 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  * Authors:
  24  *    Connor Abbott (cwabbott0@gmail.com)
  25  *
  26  */
  27
  28 #include "nir.h"
  29
  30 static bool
  31 deref_used_for_not_store(nir_deref_instr *deref)
  32 {
  33    nir_foreach_use(src, &deref->dest.ssa) {
  34       switch (src->parent_instr->type) {
  35       case nir_instr_type_deref:
  36          if (deref_used_for_not_store(nir_instr_as_deref(src->parent_instr)))
  37             return true;
  38          break;
  39
  40       case nir_instr_type_intrinsic: {
  41          nir_intrinsic_instr *intrin =
  42             nir_instr_as_intrinsic(src->parent_instr);
  43          /* The first source of copy and store intrinsics is the deref to
  44           * write.  Don't record those.
  45           */
  46          if ((intrin->intrinsic != nir_intrinsic_store_deref &&
  47               intrin->intrinsic != nir_intrinsic_copy_deref) ||
  48              src != &intrin->src[0])
  49             return true;
  50          break;
  51       }
  52
  53       default:
  54          /* If it's used by any other instruction type (most likely a texture
  55           * instruction), consider it used.
  56           */
  57          return true;
  58       }
  59    }
  60
  61    return false;
  62 }
  63
  64 static void
  65 add_var_use_deref(nir_deref_instr *deref, struct set *live)
  66 {
  67    if (deref->deref_type != nir_deref_type_var)
  68       return;
  69
  70    /* If it's not a local that never escapes the shader, then any access at
  71     * all means we need to keep it alive.
  72     */
  73    assert(deref->mode == deref->var->data.mode);
  74    if (!(deref->mode & (nir_var_local | nir_var_global | nir_var_shared)) ||
  75        deref_used_for_not_store(deref))
  76       _mesa_set_add(live, deref->var);
  77 }
  78
  79 static void
  80 add_var_use_intrinsic(nir_intrinsic_instr *instr, struct set *live,
  81                       nir_variable_mode modes)
  82 {
  83    unsigned num_vars = nir_intrinsic_infos[instr->intrinsic].num_variables;
  84
  85    switch (instr->intrinsic) {
  86    case nir_intrinsic_copy_var:
  87       _mesa_set_add(live, instr->variables[1]->var);
  88       /* Fall through */
  89    case nir_intrinsic_store_var: {
  90       /* The first source in both copy_var and store_var is the destination.
  91        * If the variable is a local that never escapes the shader, then we
  92        * don't mark it as live for just a store.
  93        */
  94       nir_variable_mode mode = instr->variables[0]->var->data.mode;
  95       if (!(mode & (nir_var_local | nir_var_global | nir_var_shared)))
  96          _mesa_set_add(live, instr->variables[0]->var);
  97       break;
  98    }
  99
 100    /* This pass can't be used on I/O variables after they've been lowered. */
 101    case nir_intrinsic_load_input:
 102       assert(!(modes & nir_var_shader_in));
 103       break;
 104    case nir_intrinsic_store_output:
 105       assert(!(modes & nir_var_shader_out));
 106       break;
 107
 108    default:
 109       for (unsigned i = 0; i < num_vars; i++) {
 110          _mesa_set_add(live, instr->variables[i]->var);
 111       }
 112       break;
 113    }
 114 }
 115
 116 static void
 117 add_var_use_call(nir_call_instr *instr, struct set *live)
 118 {
 119    if (instr->return_deref != NULL) {
 120       nir_variable *var = instr->return_deref->var;
 121       _mesa_set_add(live, var);
 122    }
 123
 124    for (unsigned i = 0; i < instr->num_params; i++) {
 125       nir_variable *var = instr->params[i]->var;
 126       _mesa_set_add(live, var);
 127    }
 128 }
 129
 130 static void
 131 add_var_use_tex(nir_tex_instr *instr, struct set *live)
 132 {
 133    if (instr->texture != NULL) {
 134       nir_variable *var = instr->texture->var;
 135       _mesa_set_add(live, var);
 136    }
 137
 138    if (instr->sampler != NULL) {
 139       nir_variable *var = instr->sampler->var;
 140       _mesa_set_add(live, var);
 141    }
 142 }
 143
 144 static void
 145 add_var_use_shader(nir_shader *shader, struct set *live, nir_variable_mode modes)
 146 {
 147    nir_foreach_function(function, shader) {
 148       if (function->impl) {
 149          nir_foreach_block(block, function->impl) {
 150             nir_foreach_instr(instr, block) {
 151                switch(instr->type) {
 152                case nir_instr_type_deref:
 153                   add_var_use_deref(nir_instr_as_deref(instr), live);
 154                   break;
 155
 156                case nir_instr_type_intrinsic:
 157                   add_var_use_intrinsic(nir_instr_as_intrinsic(instr), live,
 158                                         modes);
 159                   break;
 160
 161                case nir_instr_type_call:
 162                   add_var_use_call(nir_instr_as_call(instr), live);
 163                   break;
 164
 165                case nir_instr_type_tex:
 166                   add_var_use_tex(nir_instr_as_tex(instr), live);
 167                   break;
 168
 169                default:
 170                   break;
 171                }
 172             }
 173          }
 174       }
 175    }
 176 }
 177
 178 static void
 179 remove_dead_var_writes(nir_shader *shader, struct set *live)
 180 {
 181    nir_foreach_function(function, shader) {
 182       if (!function->impl)
 183          continue;
 184
 185       nir_foreach_block(block, function->impl) {
 186          nir_foreach_instr_safe(instr, block) {
 187             if (instr->type != nir_instr_type_intrinsic)
 188                continue;
 189
 190             nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 191             if (intrin->intrinsic != nir_intrinsic_copy_var &&
 192                 intrin->intrinsic != nir_intrinsic_store_var)
 193                continue;
 194
 195             /* Stores to dead variables need to be removed */
 196             if (intrin->variables[0]->var->data.mode == 0)
 197                nir_instr_remove(instr);
 198          }
 199       }
 200
 201       nir_foreach_block(block, function->impl) {
 202          nir_foreach_instr_safe(instr, block) {
 203             switch (instr->type) {
 204             case nir_instr_type_deref: {
 205                nir_deref_instr *deref = nir_instr_as_deref(instr);
 206
 207                nir_variable_mode parent_mode;
 208                if (deref->deref_type == nir_deref_type_var)
 209                   parent_mode = deref->var->data.mode;
 210                else
 211                   parent_mode = nir_deref_instr_parent(deref)->mode;
 212
 213                /* If the parent mode is 0, then it references a dead variable.
 214                 * Flag this deref as dead and remove it.
 215                 */
 216                if (parent_mode == 0) {
 217                   deref->mode = 0;
 218                   nir_instr_remove(&deref->instr);
 219                }
 220                break;
 221             }
 222
 223             case nir_instr_type_intrinsic: {
 224                nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
 225                if (intrin->intrinsic != nir_intrinsic_copy_deref &&
 226                    intrin->intrinsic != nir_intrinsic_store_deref)
 227                   break;
 228
 229                if (nir_src_as_deref(intrin->src[0])->mode == 0)
 230                   nir_instr_remove(instr);
 231                break;
 232             }
 233
 234             default:
 235                break; /* Nothing to do */
 236             }
 237          }
 238       }
 239    }
 240 }
 241
 242 static bool
 243 remove_dead_vars(struct exec_list *var_list, struct set *live)
 244 {
 245    bool progress = false;
 246
 247    foreach_list_typed_safe(nir_variable, var, node, var_list) {
 248       struct set_entry *entry = _mesa_set_search(live, var);
 249       if (entry == NULL) {
 250          /* Mark this variable as used by setting the mode to 0 */
 251          var->data.mode = 0;
 252          exec_node_remove(&var->node);
 253          progress = true;
 254       }
 255    }
 256
 257    return progress;
 258 }
 259
 260 bool
 261 nir_remove_dead_variables(nir_shader *shader, nir_variable_mode modes)
 262 {
 263    bool progress = false;
 264    struct set *live =
 265       _mesa_set_create(NULL, _mesa_hash_pointer, _mesa_key_pointer_equal);
 266
 267    add_var_use_shader(shader, live, modes);
 268
 269    if (modes & nir_var_uniform)
 270       progress = remove_dead_vars(&shader->uniforms, live) || progress;
 271
 272    if (modes & nir_var_shader_in)
 273       progress = remove_dead_vars(&shader->inputs, live) || progress;
 274
 275    if (modes & nir_var_shader_out)
 276       progress = remove_dead_vars(&shader->outputs, live) || progress;
 277
 278    if (modes & nir_var_global)
 279       progress = remove_dead_vars(&shader->globals, live) || progress;
 280
 281    if (modes & nir_var_system_value)
 282       progress = remove_dead_vars(&shader->system_values, live) || progress;
 283
 284    if (modes & nir_var_shared)
 285       progress = remove_dead_vars(&shader->shared, live) || progress;
 286
 287    if (modes & nir_var_local) {
 288       nir_foreach_function(function, shader) {
 289          if (function->impl) {
 290             if (remove_dead_vars(&function->impl->locals, live))
 291                progress = true;
 292          }
 293       }
 294    }
 295
 296    if (progress) {
 297       remove_dead_var_writes(shader, live);
 298
 299       nir_foreach_function(function, shader) {
 300          if (function->impl) {
 301             nir_metadata_preserve(function->impl, nir_metadata_block_index |
 302                                                   nir_metadata_dominance);
 303          }
 304       }
 305    }
 306
 307    _mesa_set_destroy(live, NULL);
 308    return progress;
 309 }