src/mesa/drivers/dri/i965/brw_fs_peephole_predicated_break.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 #include "brw_fs.h"
  25 #include "brw_cfg.h"
  26
  27 using namespace brw;
  28
  29 /** @file brw_fs_peephole_predicated_break.cpp
  30  *
  31  * Loops are often structured as
  32  *
  33  * loop:
  34  *    CMP.f0
  35  *    (+f0) IF
  36  *    BREAK
  37  *    ENDIF
  38  *    ...
  39  *    WHILE loop
  40  *
  41  * This peephole pass removes the IF and ENDIF instructions and predicates the
  42  * BREAK, dropping two instructions from the loop body.
  43  *
  44  * If the loop was a DO { ... } WHILE loop, it looks like
  45  *
  46  * loop:
  47  *    ...
  48  *    CMP.f0
  49  *    (+f0) IF
  50  *    BREAK
  51  *    ENDIF
  52  *    WHILE loop
  53  *
  54  * and we can remove the BREAK instruction and predicate the WHILE.
  55  */
  56
  57 bool
  58 fs_visitor::opt_peephole_predicated_break()
  59 {
  60    bool progress = false;
  61
  62    foreach_block (block, cfg) {
  63       if (block->start_ip != block->end_ip)
  64          continue;
  65
  66       /* BREAK and CONTINUE instructions, by definition, can only be found at
  67        * the ends of basic blocks.
  68        */
  69       backend_instruction *jump_inst = block->end();
  70       if (jump_inst->opcode != BRW_OPCODE_BREAK &&
  71           jump_inst->opcode != BRW_OPCODE_CONTINUE)
  72          continue;
  73
  74       backend_instruction *if_inst = block->prev()->end();
  75       if (if_inst->opcode != BRW_OPCODE_IF)
  76          continue;
  77
  78       backend_instruction *endif_inst = block->next()->start();
  79       if (endif_inst->opcode != BRW_OPCODE_ENDIF)
  80          continue;
  81
  82       bblock_t *jump_block = block;
  83       bblock_t *if_block = jump_block->prev();
  84       bblock_t *endif_block = jump_block->next();
  85
  86       jump_inst->predicate = if_inst->predicate;
  87       jump_inst->predicate_inverse = if_inst->predicate_inverse;
  88
  89       bblock_t *earlier_block = if_block;
  90       if (if_block->start_ip == if_block->end_ip) {
  91          earlier_block = if_block->prev();
  92       }
  93
  94       if_inst->remove(if_block);
  95
  96       bblock_t *later_block = endif_block;
  97       if (endif_block->start_ip == endif_block->end_ip) {
  98          later_block = endif_block->next();
  99       }
 100       endif_inst->remove(endif_block);
 101
 102       if (!earlier_block->ends_with_control_flow()) {
 103          earlier_block->children.make_empty();
 104          earlier_block->add_successor(cfg->mem_ctx, jump_block);
 105       }
 106
 107       if (!later_block->starts_with_control_flow()) {
 108          later_block->parents.make_empty();
 109       }
 110       jump_block->add_successor(cfg->mem_ctx, later_block);
 111
 112       if (earlier_block->can_combine_with(jump_block)) {
 113          earlier_block->combine_with(jump_block);
 114
 115          block = earlier_block;
 116       }
 117
 118       /* Now look at the first instruction of the block following the BREAK. If
 119        * it's a WHILE, we can delete the break, predicate the WHILE, and join
 120        * the two basic blocks.
 121        */
 122       bblock_t *while_block = earlier_block->next();
 123       backend_instruction *while_inst = while_block->start();
 124
 125       if (jump_inst->opcode == BRW_OPCODE_BREAK &&
 126           while_inst->opcode == BRW_OPCODE_WHILE &&
 127           while_inst->predicate == BRW_PREDICATE_NONE) {
 128          jump_inst->remove(earlier_block);
 129          while_inst->predicate = jump_inst->predicate;
 130          while_inst->predicate_inverse = !jump_inst->predicate_inverse;
 131
 132          earlier_block->children.make_empty();
 133          earlier_block->add_successor(cfg->mem_ctx, while_block);
 134
 135          assert(earlier_block->can_combine_with(while_block));
 136          earlier_block->combine_with(while_block);
 137
 138          earlier_block->next()->parents.make_empty();
 139          earlier_block->add_successor(cfg->mem_ctx, earlier_block->next());
 140       }
 141
 142       progress = true;
 143    }
 144
 145    if (progress)
 146       invalidate_live_intervals();
 147
 148    return progress;
 149 }