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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 *)
     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