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

   1 /*
   2  * Copyright © 2013 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 /** @file brw_dead_control_flow.cpp
  25  *
  26  * This file implements the dead control flow elimination optimization pass.
  27  */
  28
  29 #include "brw_shader.h"
  30 #include "brw_cfg.h"
  31
  32 /* Look for and eliminate dead control flow:
  33  *
  34  *   - if/endif
  35  *   . else in else/endif
  36  *   - if/else/endif
  37  */
  38 bool
  39 dead_control_flow_eliminate(backend_visitor *v)
  40 {
  41    bool progress = false;
  42
  43    v->calculate_cfg();
  44
  45    for (int b = 0; b < v->cfg->num_blocks; b++) {
  46       bblock_t *block = v->cfg->blocks[b];
  47       bool found = false;
  48
  49       /* ENDIF instructions, by definition, can only be found at the start of
  50        * basic blocks.
  51        */
  52       backend_instruction *endif_inst = block->start;
  53       if (endif_inst->opcode != BRW_OPCODE_ENDIF)
  54          continue;
  55
  56       backend_instruction *if_inst = NULL, *else_inst = NULL;
  57       backend_instruction *prev_inst = (backend_instruction *) endif_inst->prev;
  58       if (prev_inst->opcode == BRW_OPCODE_ELSE) {
  59          else_inst = prev_inst;
  60          found = true;
  61
  62          prev_inst = (backend_instruction *) prev_inst->prev;
  63       }
  64
  65       if (prev_inst->opcode == BRW_OPCODE_IF) {
  66          if_inst = prev_inst;
  67          found = true;
  68       } else {
  69          /* Don't remove the ENDIF if we didn't find a dead IF. */
  70          endif_inst = NULL;
  71       }
  72
  73       if (found) {
  74          if (if_inst)
  75             if_inst->remove();
  76          if (else_inst)
  77             else_inst->remove();
  78          if (endif_inst)
  79             endif_inst->remove();
  80          progress = true;
  81       }
  82    }
  83
  84    if (progress)
  85       v->invalidate_live_intervals();
  86
  87    return progress;
  88 }