workbench/libs/mesa/src/glsl/opt_redundant_jumps.cpp

   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    virtual ir_visitor_status visit_enter(ir_assignment *);
  41
  42    bool progress;
  43 };
  44
  45 /* We only care about the top level instructions, so don't descend
  46  * into expressions.
  47  */
  48 ir_visitor_status
  49 redundant_jumps_visitor::visit_enter(ir_assignment *ir)
  50 {
  51    return visit_continue_with_parent;
  52 }
  53
  54 ir_visitor_status
  55 redundant_jumps_visitor::visit_leave(ir_if *ir)
  56 {
  57    /* If the last instruction in both branches is a 'break' or a 'continue',
  58     * pull it out of the branches and insert it after the if-statment.  Note
  59     * that both must be the same type (either 'break' or 'continue').
  60     */
  61    ir_instruction *const last_then =
  62       (ir_instruction *) ir->then_instructions.get_tail();
  63    ir_instruction *const last_else =
  64       (ir_instruction *) ir->else_instructions.get_tail();
  65
  66    if ((last_then == NULL) || (last_else == NULL))
  67       return visit_continue;
  68
  69    if ((last_then->ir_type != ir_type_loop_jump)
  70        || (last_else->ir_type != ir_type_loop_jump))
  71       return visit_continue;
  72
  73    ir_loop_jump *const then_jump = (ir_loop_jump *) last_then;
  74    ir_loop_jump *const else_jump = (ir_loop_jump *) last_else;
  75
  76    if (then_jump->mode != else_jump->mode)
  77       return visit_continue;
  78
  79    then_jump->remove();
  80    else_jump->remove();
  81    this->progress = true;
  82
  83    ir->insert_after(then_jump);
  84
  85    /* If both branchs of the if-statement are now empty, remove the
  86     * if-statement.
  87     */
  88    if (ir->then_instructions.is_empty() && ir->else_instructions.is_empty())
  89       ir->remove();
  90
  91    return visit_continue;
  92 }
  93
  94
  95 ir_visitor_status
  96 redundant_jumps_visitor::visit_leave(ir_loop *ir)
  97 {
  98    /* If the last instruction of a loop body is a 'continue', remove it.
  99     */
 100    ir_instruction *const last =
 101       (ir_instruction *) ir->body_instructions.get_tail();
 102
 103    if (last && (last->ir_type == ir_type_loop_jump)
 104        && (((ir_loop_jump *) last)->mode == ir_loop_jump::jump_continue)) {
 105       last->remove();
 106       this->progress = true;
 107    }
 108
 109    return visit_continue;
 110 }
 111
 112
 113 bool
 114 optimize_redundant_jumps(exec_list *instructions)
 115 {
 116    redundant_jumps_visitor v;
 117
 118    v.run(instructions);
 119    return v.progress;
 120 }