src/glsl/ir_constant_folding.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 ir_constant_folding.cpp
  26  * Replace constant-valued expressions with references to constant values.
  27  */
  28
  29 #include "ir.h"
  30 #include "ir_visitor.h"
  31 #include "ir_rvalue_visitor.h"
  32 #include "ir_optimization.h"
  33 #include "glsl_types.h"
  34
  35 /**
  36  * Visitor class for replacing expressions with ir_constant values.
  37  */
  38
  39 class ir_constant_folding_visitor : public ir_rvalue_visitor {
  40 public:
  41    ir_constant_folding_visitor()
  42    {
  43       this->progress = false;
  44    }
  45
  46    virtual ~ir_constant_folding_visitor()
  47    {
  48       /* empty */
  49    }
  50
  51    virtual ir_visitor_status visit_enter(ir_assignment *ir);
  52    virtual ir_visitor_status visit_enter(ir_call *ir);
  53
  54    virtual void handle_rvalue(ir_rvalue **rvalue);
  55
  56    bool progress;
  57 };
  58
  59 void
  60 ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
  61 {
  62    if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
  63       return;
  64
  65    ir_constant *constant = (*rvalue)->constant_expression_value();
  66    if (constant) {
  67       *rvalue = constant;
  68       this->progress = true;
  69    } else {
  70       (*rvalue)->accept(this);
  71    }
  72 }
  73
  74 ir_visitor_status
  75 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
  76 {
  77    ir->rhs->accept(this);
  78    handle_rvalue(&ir->rhs);
  79
  80    if (ir->condition) {
  81       ir->condition->accept(this);
  82       handle_rvalue(&ir->condition);
  83
  84       ir_constant *const_val = ir->condition->as_constant();
  85       /* If the condition is constant, either remove the condition or
  86        * remove the never-executed assignment.
  87        */
  88       if (const_val) {
  89          if (const_val->value.b[0])
  90             ir->condition = NULL;
  91          else
  92             ir->remove();
  93          this->progress = true;
  94       }
  95    }
  96
  97    /* Don't descend into the LHS because we want it to stay as a
  98     * variable dereference.  FINISHME: We probably should to get array
  99     * indices though.
 100     */
 101    return visit_continue_with_parent;
 102 }
 103
 104 ir_visitor_status
 105 ir_constant_folding_visitor::visit_enter(ir_call *ir)
 106 {
 107    exec_list_iterator sig_iter = ir->get_callee()->parameters.iterator();
 108    foreach_iter(exec_list_iterator, iter, *ir) {
 109       ir_rvalue *param_rval = (ir_rvalue *)iter.get();
 110       ir_variable *sig_param = (ir_variable *)sig_iter.get();
 111
 112       if (sig_param->mode == ir_var_in) {
 113          ir_rvalue *new_param = param_rval;
 114
 115          handle_rvalue(&new_param);
 116          if (new_param != param_rval) {
 117             param_rval->replace_with(new_param);
 118          }
 119       }
 120       sig_iter.next();
 121    }
 122
 123    return visit_continue_with_parent;
 124 }
 125
 126 bool
 127 do_constant_folding(exec_list *instructions)
 128 {
 129    ir_constant_folding_visitor constant_folding;
 130
 131    visit_list_elements(&constant_folding, instructions);
 132
 133    return constant_folding.progress;
 134 }