src/glsl/opt_if_simplification.cpp

   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 }