src/compiler/nir/nir_opt_dce.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 /* SSA-based mark-and-sweep dead code elimination */
  31
  32 typedef struct {
  33    struct exec_node node;
  34    nir_instr *instr;
  35 } worklist_elem;
  36
  37 static void
  38 worklist_push(struct exec_list *worklist, nir_instr *instr)
  39 {
  40    worklist_elem *elem = ralloc(worklist, worklist_elem);
  41    elem->instr = instr;
  42    instr->pass_flags = 1;
  43    exec_list_push_tail(worklist, &elem->node);
  44 }
  45
  46 static nir_instr *
  47 worklist_pop(struct exec_list *worklist)
  48 {
  49    struct exec_node *node = exec_list_pop_head(worklist);
  50    worklist_elem *elem = exec_node_data(worklist_elem, node, node);
  51    return elem->instr;
  52 }
  53
  54 static bool
  55 mark_live_cb(nir_src *src, void *_state)
  56 {
  57    struct exec_list *worklist = (struct exec_list *) _state;
  58
  59    if (src->is_ssa && !src->ssa->parent_instr->pass_flags) {
  60       worklist_push(worklist, src->ssa->parent_instr);
  61    }
  62
  63    return true;
  64 }
  65
  66 static void
  67 init_instr(nir_instr *instr, struct exec_list *worklist)
  68 {
  69    nir_alu_instr *alu_instr;
  70    nir_intrinsic_instr *intrin_instr;
  71    nir_tex_instr *tex_instr;
  72
  73    /* We use the pass_flags to store the live/dead information.  In DCE, we
  74     * just treat it as a zero/non-zero boolean for whether or not the
  75     * instruction is live.
  76     */
  77    instr->pass_flags = 0;
  78
  79    switch (instr->type) {
  80    case nir_instr_type_call:
  81    case nir_instr_type_jump:
  82       worklist_push(worklist, instr);
  83       break;
  84
  85    case nir_instr_type_alu:
  86       alu_instr = nir_instr_as_alu(instr);
  87       if (!alu_instr->dest.dest.is_ssa)
  88          worklist_push(worklist, instr);
  89       break;
  90
  91    case nir_instr_type_intrinsic:
  92       intrin_instr = nir_instr_as_intrinsic(instr);
  93       if (nir_intrinsic_infos[intrin_instr->intrinsic].flags &
  94           NIR_INTRINSIC_CAN_ELIMINATE) {
  95          if (nir_intrinsic_infos[intrin_instr->intrinsic].has_dest &&
  96              !intrin_instr->dest.is_ssa) {
  97             worklist_push(worklist, instr);
  98          }
  99       } else {
 100          worklist_push(worklist, instr);
 101       }
 102       break;
 103
 104    case nir_instr_type_tex:
 105       tex_instr = nir_instr_as_tex(instr);
 106       if (!tex_instr->dest.is_ssa)
 107          worklist_push(worklist, instr);
 108       break;
 109
 110    default:
 111       break;
 112    }
 113 }
 114
 115 static bool
 116 init_block(nir_block *block, struct exec_list *worklist)
 117 {
 118    nir_foreach_instr(instr, block)
 119       init_instr(instr, worklist);
 120
 121    nir_if *following_if = nir_block_get_following_if(block);
 122    if (following_if) {
 123       if (following_if->condition.is_ssa &&
 124           !following_if->condition.ssa->parent_instr->pass_flags)
 125          worklist_push(worklist, following_if->condition.ssa->parent_instr);
 126    }
 127
 128    return true;
 129 }
 130
 131 static bool
 132 nir_opt_dce_impl(nir_function_impl *impl)
 133 {
 134    struct exec_list *worklist = rzalloc(NULL, struct exec_list);
 135    exec_list_make_empty(worklist);
 136
 137    nir_foreach_block(block, impl) {
 138       init_block(block, worklist);
 139    }
 140
 141    while (!exec_list_is_empty(worklist)) {
 142       nir_instr *instr = worklist_pop(worklist);
 143       nir_foreach_src(instr, mark_live_cb, worklist);
 144    }
 145
 146    ralloc_free(worklist);
 147
 148    bool progress = false;
 149
 150    nir_foreach_block(block, impl) {
 151       nir_foreach_instr_safe(instr, block) {
 152          if (!instr->pass_flags) {
 153             nir_instr_remove(instr);
 154             progress = true;
 155          }
 156       }
 157    }
 158
 159    if (progress)
 160       nir_metadata_preserve(impl, nir_metadata_block_index |
 161                                   nir_metadata_dominance);
 162
 163    return progress;
 164 }
 165
 166 bool
 167 nir_opt_dce(nir_shader *shader)
 168 {
 169    bool progress = false;
 170    nir_foreach_function(function, shader) {
 171       if (function->impl && nir_opt_dce_impl(function->impl))
 172          progress = true;
 173    }
 174
 175    return progress;
 176 }