src/compiler/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 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 *)
  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 }