src/intel/compiler/brw_vec4_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_vec4.h"
  25 #include "brw_vec4_live_variables.h"
  26 #include "brw_cfg.h"
  27
  28 /** @file brw_vec4_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 using namespace brw;
  38
  39 bool
  40 vec4_visitor::dead_code_eliminate()
  41 {
  42    bool progress = false;
  43
  44    calculate_live_intervals();
  45
  46    int num_vars = live_intervals->num_vars;
  47    BITSET_WORD *live = rzalloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
  48    BITSET_WORD *flag_live = rzalloc_array(NULL, BITSET_WORD, 1);
  49
  50    foreach_block_reverse_safe(block, cfg) {
  51       memcpy(live, live_intervals->block_data[block->num].liveout,
  52              sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
  53       memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout,
  54              sizeof(BITSET_WORD));
  55
  56       foreach_inst_in_block_reverse_safe(vec4_instruction, inst, block) {
  57          if ((inst->dst.file == VGRF && !inst->has_side_effects()) ||
  58              (inst->dst.is_null() && inst->writes_flag())){
  59             bool result_live[4] = { false };
  60             if (inst->dst.file == VGRF) {
  61                for (unsigned i = 0; i < DIV_ROUND_UP(inst->size_written, 16); i++) {
  62                   for (int c = 0; c < 4; c++) {
  63                      const unsigned v = var_from_reg(alloc, inst->dst, c, i);
  64                      result_live[c] |= BITSET_TEST(live, v);
  65                   }
  66                }
  67             } else {
  68                for (unsigned c = 0; c < 4; c++)
  69                   result_live[c] = BITSET_TEST(flag_live, c);
  70             }
  71
  72             /* If the instruction can't do writemasking, then it's all or
  73              * nothing.
  74              */
  75             if (!inst->can_do_writemask(devinfo)) {
  76                bool result = result_live[0] | result_live[1] |
  77                              result_live[2] | result_live[3];
  78                result_live[0] = result;
  79                result_live[1] = result;
  80                result_live[2] = result;
  81                result_live[3] = result;
  82             }
  83
  84             for (int c = 0; c < 4; c++) {
  85                if (!result_live[c] && inst->dst.writemask & (1 << c)) {
  86                   inst->dst.writemask &= ~(1 << c);
  87                   progress = true;
  88
  89                   if (inst->dst.writemask == 0) {
  90                      if (inst->writes_accumulator || inst->writes_flag()) {
  91                         inst->dst = dst_reg(retype(brw_null_reg(), inst->dst.type));
  92                      } else {
  93                         inst->opcode = BRW_OPCODE_NOP;
  94                         break;
  95                      }
  96                   }
  97                }
  98             }
  99          }
 100
 101          if (inst->dst.is_null() && inst->writes_flag()) {
 102             bool combined_live = false;
 103             for (unsigned c = 0; c < 4; c++)
 104                combined_live |= BITSET_TEST(flag_live, c);
 105
 106             if (!combined_live) {
 107                inst->opcode = BRW_OPCODE_NOP;
 108                progress = true;
 109             }
 110          }
 111
 112          if (inst->dst.file == VGRF && !inst->predicate &&
 113              !inst->is_align1_partial_write()) {
 114             for (unsigned i = 0; i < DIV_ROUND_UP(inst->size_written, 16); i++) {
 115                for (int c = 0; c < 4; c++) {
 116                   if (inst->dst.writemask & (1 << c)) {
 117                      const unsigned v = var_from_reg(alloc, inst->dst, c, i);
 118                      BITSET_CLEAR(live, v);
 119                   }
 120                }
 121             }
 122          }
 123
 124          if (inst->writes_flag() && !inst->predicate) {
 125             for (unsigned c = 0; c < 4; c++)
 126                BITSET_CLEAR(flag_live, c);
 127          }
 128
 129          if (inst->opcode == BRW_OPCODE_NOP) {
 130             inst->remove(block);
 131             continue;
 132          }
 133
 134          for (int i = 0; i < 3; i++) {
 135             if (inst->src[i].file == VGRF) {
 136                for (unsigned j = 0; j < DIV_ROUND_UP(inst->size_read(i), 16); j++) {
 137                   for (int c = 0; c < 4; c++) {
 138                      const unsigned v = var_from_reg(alloc, inst->src[i], c, j);
 139                      BITSET_SET(live, v);
 140                   }
 141                }
 142             }
 143          }
 144
 145          for (unsigned c = 0; c < 4; c++) {
 146             if (inst->reads_flag(c)) {
 147                BITSET_SET(flag_live, c);
 148             }
 149          }
 150       }
 151    }
 152
 153    ralloc_free(live);
 154    ralloc_free(flag_live);
 155
 156    if (progress)
 157       invalidate_live_intervals();
 158
 159    return progress;
 160 }