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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_if_simplification.cpp
     26  *
     27  * Moves constant branches of if statements out to the surrounding
     28  * instruction stream.
     29  */
     30 
     31 #include "ir.h"
     32 
     33 class ir_if_simplification_visitor : public ir_hierarchical_visitor {
     34 public:
     35    ir_if_simplification_visitor()
     36    {
     37       this->made_progress = false;
     38    }
     39 
     40    ir_visitor_status visit_leave(ir_if *);
     41 
     42    bool made_progress;
     43 };
     44 
     45 bool
     46 do_if_simplification(exec_list *instructions)
     47 {
     48    ir_if_simplification_visitor v;
     49 
     50    v.run(instructions);
     51    return v.made_progress;
     52 }
     53 
     54 
     55 ir_visitor_status
     56 ir_if_simplification_visitor::visit_leave(ir_if *ir)
     57 {
     58    /* FINISHME: Ideally there would be a way to note that the condition results
     59     * FINISHME: in a constant before processing both of the other subtrees.
     60     * FINISHME: This can probably be done with some flags, but it would take
     61     * FINISHME: some work to get right.
     62     */
     63    ir_constant *condition_constant = ir->condition->constant_expression_value();
     64    if (condition_constant) {
     65       /* Move the contents of the one branch of the conditional
     66        * that matters out.
     67        */
     68       if (condition_constant->value.b[0]) {
     69 	 foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
     70 	    ir_instruction *then_ir = (ir_instruction *)then_iter.get();
     71 	    ir->insert_before(then_ir);
     72 	 }
     73       } else {
     74 	 foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
     75 	    ir_instruction *else_ir = (ir_instruction *)else_iter.get();
     76 	    ir->insert_before(else_ir);
     77 	 }
     78       }
     79       ir->remove();
     80       this->made_progress = true;
     81    }
     82 
     83    return visit_continue;
     84 }
     85