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