src/glsl/opt_redundant_jumps.cpp

/*
 * Copyright © 2010 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

/**
 * \file opt_redundant_jumps.cpp
 * Remove certain types of redundant jumps
 */

#include "ir.h"

namespace {

class redundant_jumps_visitor : public ir_hierarchical_visitor {
public:
   redundant_jumps_visitor()
   {
      this->progress = false;
   }

   virtual ir_visitor_status visit_leave(ir_if *);
   virtual ir_visitor_status visit_leave(ir_loop *);
   virtual ir_visitor_status visit_enter(ir_assignment *);

   bool progress;
};

} /* unnamed namespace */

/* We only care about the top level instructions, so don't descend
 * into expressions.
 */
ir_visitor_status
redundant_jumps_visitor::visit_enter(ir_assignment *)
{
   return visit_continue_with_parent;
}

ir_visitor_status
redundant_jumps_visitor::visit_leave(ir_if *ir)
{
   /* If the last instruction in both branches is a 'break' or a 'continue',
    * pull it out of the branches and insert it after the if-statment.  Note
    * that both must be the same type (either 'break' or 'continue').
    */
   ir_instruction *const last_then =
      (ir_instruction *) ir->then_instructions.get_tail();
   ir_instruction *const last_else =
      (ir_instruction *) ir->else_instructions.get_tail();

   if ((last_then == NULL) || (last_else == NULL))
      return visit_continue;

   if ((last_then->ir_type != ir_type_loop_jump)
       || (last_else->ir_type != ir_type_loop_jump))
      return visit_continue;

   ir_loop_jump *const then_jump = (ir_loop_jump *) last_then;
   ir_loop_jump *const else_jump = (ir_loop_jump *) last_else;

   if (then_jump->mode != else_jump->mode)
      return visit_continue;

   then_jump->remove();
   else_jump->remove();
   this->progress = true;

   ir->insert_after(then_jump);

   /* If both branchs of the if-statement are now empty, remove the
    * if-statement.
    */
   if (ir->then_instructions.is_empty() && ir->else_instructions.is_empty())
      ir->remove();

   return visit_continue;
}


ir_visitor_status
redundant_jumps_visitor::visit_leave(ir_loop *ir)
{
   /* If the last instruction of a loop body is a 'continue', remove it.
    */
   ir_instruction *const last =
      (ir_instruction *) ir->body_instructions.get_tail();

   if (last && (last->ir_type == ir_type_loop_jump)
       && (((ir_loop_jump *) last)->mode == ir_loop_jump::jump_continue)) {
      last->remove();
      this->progress = true;
   }

   return visit_continue;
}


bool
optimize_redundant_jumps(exec_list *instructions)
{
   redundant_jumps_visitor v;

   v.run(instructions);
   return v.progress;
}