src/mesa/drivers/dri/i965/brw_fs_dead_code_eliminate.cpp

   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
  24 #include "brw_fs.h"
  25 #include "brw_fs_live_variables.h"
  26 #include "brw_cfg.h"
  27
  28 /** @file brw_fs_dead_code_eliminate.cpp
  29  *
  30  * Dataflow-aware dead code elimination.
  31  *
  32  * Walks the instruction list from the bottom, removing instructions that
  33  * have results that both aren't used in later blocks and haven't been read
  34  * yet in the tail end of this block.
  35  */
  36
  37 bool
  38 fs_visitor::dead_code_eliminate()
  39 {
  40    bool progress = false;
  41
  42    calculate_live_intervals();
  43
  44    int num_vars = live_intervals->num_vars;
  45    BITSET_WORD *live = ralloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
  46
  47    foreach_block (block, cfg) {
  48       memcpy(live, live_intervals->bd[block->num].liveout,
  49              sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
  50
  51       foreach_inst_in_block_reverse(fs_inst, inst, block) {
  52          if (inst->dst.file == GRF &&
  53              !inst->has_side_effects() &&
  54              !inst->writes_flag()) {
  55             bool result_live = false;
  56
  57             if (inst->regs_written == 1) {
  58                int var = live_intervals->var_from_reg(&inst->dst);
  59                result_live = BITSET_TEST(live, var);
  60             } else {
  61                int var = live_intervals->var_from_vgrf[inst->dst.reg];
  62                for (int i = 0; i < inst->regs_written; i++) {
  63                   result_live = result_live || BITSET_TEST(live, var + i);
  64                }
  65             }
  66
  67             if (!result_live) {
  68                progress = true;
  69
  70                if (inst->writes_accumulator) {
  71                   inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
  72                } else {
  73                   inst->opcode = BRW_OPCODE_NOP;
  74                   continue;
  75                }
  76             }
  77          }
  78
  79          if (inst->dst.file == GRF) {
  80             if (!inst->is_partial_write()) {
  81                int var = live_intervals->var_from_vgrf[inst->dst.reg];
  82                for (int i = 0; i < inst->regs_written; i++) {
  83                   BITSET_CLEAR(live, var + inst->dst.reg_offset + i);
  84                }
  85             }
  86          }
  87
  88          for (int i = 0; i < inst->sources; i++) {
  89             if (inst->src[i].file == GRF) {
  90                int var = live_intervals->var_from_vgrf[inst->src[i].reg];
  91
  92                for (int j = 0; j < inst->regs_read(this, i); j++) {
  93                   BITSET_SET(live, var + inst->src[i].reg_offset + j);
  94                }
  95             }
  96          }
  97       }
  98    }
  99
 100    ralloc_free(live);
 101
 102    if (progress) {
 103       foreach_in_list_safe(fs_inst, inst, &instructions) {
 104          if (inst->opcode == BRW_OPCODE_NOP) {
 105             inst->remove();
 106          }
 107       }
 108
 109       invalidate_live_intervals();
 110    }
 111
 112    return progress;
 113 }