Home | History | Annotate | Download | only in glsl 
      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 namespace {
     34 
     35 class ir_if_simplification_visitor : public ir_hierarchical_visitor {
     36 public:
     37    ir_if_simplification_visitor()
     38    {
     39       this->made_progress = false;
     40    }
     41 
     42    ir_visitor_status visit_leave(ir_if *);
     43    ir_visitor_status visit_enter(ir_assignment *);
     44 
     45    bool made_progress;
     46 };
     47 
     48 } /* unnamed namespace */
     49 
     50 /* We only care about the top level "if" instructions, so don't
     51  * descend into expressions.
     52  */
     53 ir_visitor_status
     54 ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
     55 {
     56    (void) ir;
     57    return visit_continue_with_parent;
     58 }
     59 
     60 bool
     61 do_if_simplification(exec_list *instructions)
     62 {
     63    ir_if_simplification_visitor v;
     64 
     65    v.run(instructions);
     66    return v.made_progress;
     67 }
     68 
     69 
     70 ir_visitor_status
     71 ir_if_simplification_visitor::visit_leave(ir_if *ir)
     72 {
     73    /* If the if statement has nothing on either side, remove it. */
     74    if (ir->then_instructions.is_empty() &&
     75        ir->else_instructions.is_empty()) {
     76       ir->remove();
     77       this->made_progress = true;
     78       return visit_continue;
     79    }
     80 
     81    /* FINISHME: Ideally there would be a way to note that the condition results
     82     * FINISHME: in a constant before processing both of the other subtrees.
     83     * FINISHME: This can probably be done with some flags, but it would take
     84     * FINISHME: some work to get right.
     85     */
     86    ir_constant *condition_constant = ir->condition->constant_expression_value();
     87    if (condition_constant) {
     88       /* Move the contents of the one branch of the conditional
     89        * that matters out.
     90        */
     91       if (condition_constant->value.b[0]) {
     92 	 foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
     93 	    ir_instruction *then_ir = (ir_instruction *)then_iter.get();
     94 	    ir->insert_before(then_ir);
     95 	 }
     96       } else {
     97 	 foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
     98 	    ir_instruction *else_ir = (ir_instruction *)else_iter.get();
     99 	    ir->insert_before(else_ir);
    100 	 }
    101       }
    102       ir->remove();
    103       this->made_progress = true;
    104    }
    105 
    106    return visit_continue;
    107 }
    108