src/glsl/opt_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 opt_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    /* Note that we do rvalue visitoring on leaving.  So if an
  66     * expression has a non-constant operand, no need to go looking
  67     * down it to find if it's constant.  This cuts the time of this
  68     * pass down drastically.
  69     */
  70    ir_expression *expr = (*rvalue)->as_expression();
  71    if (expr) {
  72       for (unsigned int i = 0; i < expr->get_num_operands(); i++) {
  73          if (!expr->operands[i]->as_constant())
  74             return;
  75       }
  76    }
  77
  78    ir_constant *constant = (*rvalue)->constant_expression_value();
  79    if (constant) {
  80       *rvalue = constant;
  81       this->progress = true;
  82    } else {
  83       (*rvalue)->accept(this);
  84    }
  85 }
  86
  87 ir_visitor_status
  88 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
  89 {
  90    ir->rhs->accept(this);
  91    handle_rvalue(&ir->rhs);
  92
  93    if (ir->condition) {
  94       ir->condition->accept(this);
  95       handle_rvalue(&ir->condition);
  96
  97       ir_constant *const_val = ir->condition->as_constant();
  98       /* If the condition is constant, either remove the condition or
  99        * remove the never-executed assignment.
 100        */
 101       if (const_val) {
 102          if (const_val->value.b[0])
 103             ir->condition = NULL;
 104          else
 105             ir->remove();
 106          this->progress = true;
 107       }
 108    }
 109
 110    /* Don't descend into the LHS because we want it to stay as a
 111     * variable dereference.  FINISHME: We probably should to get array
 112     * indices though.
 113     */
 114    return visit_continue_with_parent;
 115 }
 116
 117 ir_visitor_status
 118 ir_constant_folding_visitor::visit_enter(ir_call *ir)
 119 {
 120    exec_list_iterator sig_iter = ir->get_callee()->parameters.iterator();
 121    foreach_iter(exec_list_iterator, iter, *ir) {
 122       ir_rvalue *param_rval = (ir_rvalue *)iter.get();
 123       ir_variable *sig_param = (ir_variable *)sig_iter.get();
 124
 125       if (sig_param->mode == ir_var_in || sig_param->mode == ir_var_const_in) {
 126          ir_rvalue *new_param = param_rval;
 127
 128          handle_rvalue(&new_param);
 129          if (new_param != param_rval) {
 130             param_rval->replace_with(new_param);
 131          }
 132       }
 133       sig_iter.next();
 134    }
 135
 136    return visit_continue_with_parent;
 137 }
 138
 139 bool
 140 do_constant_folding(exec_list *instructions)
 141 {
 142    ir_constant_folding_visitor constant_folding;
 143
 144    visit_list_elements(&constant_folding, instructions);
 145
 146    return constant_folding.progress;
 147 }