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  1. /*
  2.  * Copyright © 2010 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
  21.  * DEALINGS IN THE SOFTWARE.
  22.  */
  23.  
  24. /**
  25.  * \file opt_redundant_jumps.cpp
  26.  * Remove certain types of redundant jumps
  27.  */
  28.  
  29. #include "ir.h"
  30.  
  31. namespace {
  32.  
  33. class redundant_jumps_visitor : public ir_hierarchical_visitor {
  34. public:
  35.    redundant_jumps_visitor()
  36.    {
  37.       this->progress = false;
  38.    }
  39.  
  40.    virtual ir_visitor_status visit_leave(ir_if *);
  41.    virtual ir_visitor_status visit_leave(ir_loop *);
  42.    virtual ir_visitor_status visit_enter(ir_assignment *);
  43.  
  44.    bool progress;
  45. };
  46.  
  47. } /* unnamed namespace */
  48.  
  49. /* We only care about the top level instructions, so don't descend
  50.  * into expressions.
  51.  */
  52. ir_visitor_status
  53. redundant_jumps_visitor::visit_enter(ir_assignment *ir)
  54. {
  55.    return visit_continue_with_parent;
  56. }
  57.  
  58. ir_visitor_status
  59. redundant_jumps_visitor::visit_leave(ir_if *ir)
  60. {
  61.    /* If the last instruction in both branches is a 'break' or a 'continue',
  62.     * pull it out of the branches and insert it after the if-statment.  Note
  63.     * that both must be the same type (either 'break' or 'continue').
  64.     */
  65.    ir_instruction *const last_then =
  66.       (ir_instruction *) ir->then_instructions.get_tail();
  67.    ir_instruction *const last_else =
  68.       (ir_instruction *) ir->else_instructions.get_tail();
  69.  
  70.    if ((last_then == NULL) || (last_else == NULL))
  71.       return visit_continue;
  72.  
  73.    if ((last_then->ir_type != ir_type_loop_jump)
  74.        || (last_else->ir_type != ir_type_loop_jump))
  75.       return visit_continue;
  76.  
  77.    ir_loop_jump *const then_jump = (ir_loop_jump *) last_then;
  78.    ir_loop_jump *const else_jump = (ir_loop_jump *) last_else;
  79.  
  80.    if (then_jump->mode != else_jump->mode)
  81.       return visit_continue;
  82.  
  83.    then_jump->remove();
  84.    else_jump->remove();
  85.    this->progress = true;
  86.  
  87.    ir->insert_after(then_jump);
  88.  
  89.    /* If both branchs of the if-statement are now empty, remove the
  90.     * if-statement.
  91.     */
  92.    if (ir->then_instructions.is_empty() && ir->else_instructions.is_empty())
  93.       ir->remove();
  94.  
  95.    return visit_continue;
  96. }
  97.  
  98.  
  99. ir_visitor_status
  100. redundant_jumps_visitor::visit_leave(ir_loop *ir)
  101. {
  102.    /* If the last instruction of a loop body is a 'continue', remove it.
  103.     */
  104.    ir_instruction *const last =
  105.       (ir_instruction *) ir->body_instructions.get_tail();
  106.  
  107.    if (last && (last->ir_type == ir_type_loop_jump)
  108.        && (((ir_loop_jump *) last)->mode == ir_loop_jump::jump_continue)) {
  109.       last->remove();
  110.       this->progress = true;
  111.    }
  112.  
  113.    return visit_continue;
  114. }
  115.  
  116.  
  117. bool
  118. optimize_redundant_jumps(exec_list *instructions)
  119. {
  120.    redundant_jumps_visitor v;
  121.  
  122.    v.run(instructions);
  123.    return v.progress;
  124. }
  125.