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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. class redundant_jumps_visitor : public ir_hierarchical_visitor {
  32. public:
  33.    redundant_jumps_visitor()
  34.    {
  35.       this->progress = false;
  36.    }
  37.  
  38.    virtual ir_visitor_status visit_leave(ir_if *);
  39.    virtual ir_visitor_status visit_leave(ir_loop *);
  40.  
  41.    bool progress;
  42. };
  43.  
  44.  
  45. ir_visitor_status
  46. redundant_jumps_visitor::visit_leave(ir_if *ir)
  47. {
  48.    /* If the last instruction in both branches is a 'break' or a 'continue',
  49.     * pull it out of the branches and insert it after the if-statment.  Note
  50.     * that both must be the same type (either 'break' or 'continue').
  51.     */
  52.    ir_instruction *const last_then =
  53.       (ir_instruction *) ir->then_instructions.get_tail();
  54.    ir_instruction *const last_else =
  55.       (ir_instruction *) ir->else_instructions.get_tail();
  56.  
  57.    if ((last_then == NULL) || (last_else == NULL))
  58.       return visit_continue;
  59.  
  60.    if ((last_then->ir_type != ir_type_loop_jump)
  61.        || (last_else->ir_type != ir_type_loop_jump))
  62.       return visit_continue;
  63.  
  64.    ir_loop_jump *const then_jump = (ir_loop_jump *) last_then;
  65.    ir_loop_jump *const else_jump = (ir_loop_jump *) last_else;
  66.  
  67.    if (then_jump->mode != else_jump->mode)
  68.       return visit_continue;
  69.  
  70.    then_jump->remove();
  71.    else_jump->remove();
  72.    this->progress = true;
  73.  
  74.    ir->insert_after(then_jump);
  75.  
  76.    /* If both branchs of the if-statement are now empty, remove the
  77.     * if-statement.
  78.     */
  79.    if (ir->then_instructions.is_empty() && ir->else_instructions.is_empty())
  80.       ir->remove();
  81.  
  82.    return visit_continue;
  83. }
  84.  
  85.  
  86. ir_visitor_status
  87. redundant_jumps_visitor::visit_leave(ir_loop *ir)
  88. {
  89.    /* If the last instruction of a loop body is a 'continue', remove it.
  90.     */
  91.    ir_instruction *const last =
  92.       (ir_instruction *) ir->body_instructions.get_tail();
  93.  
  94.    if (last && (last->ir_type == ir_type_loop_jump)
  95.        && (((ir_loop_jump *) last)->mode == ir_loop_jump::jump_continue)) {
  96.       last->remove();
  97.       this->progress = true;
  98.    }
  99.  
  100.    return visit_continue;
  101. }
  102.  
  103.  
  104. bool
  105. optimize_redundant_jumps(exec_list *instructions)
  106. {
  107.    redundant_jumps_visitor v;
  108.  
  109.    v.run(instructions);
  110.    return v.progress;
  111. }
  112.