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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