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 namespace {
  36
  37 /**
  38  * Visitor class for replacing expressions with ir_constant values.
  39  */
  40
  41 class ir_constant_folding_visitor : public ir_rvalue_visitor {
  42 public:
  43    ir_constant_folding_visitor()
  44    {
  45       this->progress = false;
  46    }
  47
  48    virtual ~ir_constant_folding_visitor()
  49    {
  50       /* empty */
  51    }
  52
  53    virtual ir_visitor_status visit_enter(ir_assignment *ir);
  54    virtual ir_visitor_status visit_enter(ir_call *ir);
  55
  56    virtual void handle_rvalue(ir_rvalue **rvalue);
  57
  58    bool progress;
  59 };
  60
  61 } /* unnamed namespace */
  62
  63 void
  64 ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
  65 {
  66    if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
  67       return;
  68
  69    /* Note that we do rvalue visitoring on leaving.  So if an
  70     * expression has a non-constant operand, no need to go looking
  71     * down it to find if it's constant.  This cuts the time of this
  72     * pass down drastically.
  73     */
  74    ir_expression *expr = (*rvalue)->as_expression();
  75    if (expr) {
  76       for (unsigned int i = 0; i < expr->get_num_operands(); i++) {
  77          if (!expr->operands[i]->as_constant())
  78             return;
  79       }
  80    }
  81
  82    ir_constant *constant = (*rvalue)->constant_expression_value();
  83    if (constant) {
  84       *rvalue = constant;
  85       this->progress = true;
  86    } else {
  87       (*rvalue)->accept(this);
  88    }
  89 }
  90
  91 ir_visitor_status
  92 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
  93 {
  94    ir->rhs->accept(this);
  95    handle_rvalue(&ir->rhs);
  96
  97    if (ir->condition) {
  98       ir->condition->accept(this);
  99       handle_rvalue(&ir->condition);
 100
 101       ir_constant *const_val = ir->condition->as_constant();
 102       /* If the condition is constant, either remove the condition or
 103        * remove the never-executed assignment.
 104        */
 105       if (const_val) {
 106          if (const_val->value.b[0])
 107             ir->condition = NULL;
 108          else
 109             ir->remove();
 110          this->progress = true;
 111       }
 112    }
 113
 114    /* Don't descend into the LHS because we want it to stay as a
 115     * variable dereference.  FINISHME: We probably should to get array
 116     * indices though.
 117     */
 118    return visit_continue_with_parent;
 119 }
 120
 121 ir_visitor_status
 122 ir_constant_folding_visitor::visit_enter(ir_call *ir)
 123 {
 124    /* Attempt to constant fold parameters */
 125    exec_list_iterator sig_iter = ir->callee->parameters.iterator();
 126    foreach_iter(exec_list_iterator, iter, *ir) {
 127       ir_rvalue *param_rval = (ir_rvalue *)iter.get();
 128       ir_variable *sig_param = (ir_variable *)sig_iter.get();
 129
 130       if (sig_param->data.mode == ir_var_function_in
 131           || sig_param->data.mode == ir_var_const_in) {
 132          ir_rvalue *new_param = param_rval;
 133
 134          handle_rvalue(&new_param);
 135          if (new_param != param_rval) {
 136             param_rval->replace_with(new_param);
 137          }
 138       }
 139       sig_iter.next();
 140    }
 141
 142    /* Next, see if the call can be replaced with an assignment of a constant */
 143    ir_constant *const_val = ir->constant_expression_value();
 144
 145    if (const_val != NULL) {
 146       ir_assignment *assignment =
 147          new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
 148       ir->replace_with(assignment);
 149    }
 150
 151    return visit_continue_with_parent;
 152 }
 153
 154 bool
 155 do_constant_folding(exec_list *instructions)
 156 {
 157    ir_constant_folding_visitor constant_folding;
 158
 159    visit_list_elements(&constant_folding, instructions);
 160
 161    return constant_folding.progress;
 162 }