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    /* Ditto for swizzles. */
  83    ir_swizzle *swiz = (*rvalue)->as_swizzle();
  84    if (swiz && !swiz->val->as_constant())
  85       return;
  86
  87    ir_constant *constant = (*rvalue)->constant_expression_value();
  88    if (constant) {
  89       *rvalue = constant;
  90       this->progress = true;
  91    } else {
  92       (*rvalue)->accept(this);
  93    }
  94 }
  95
  96 ir_visitor_status
  97 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
  98 {
  99    ir->rhs->accept(this);
 100    handle_rvalue(&ir->rhs);
 101
 102    if (ir->condition) {
 103       ir->condition->accept(this);
 104       handle_rvalue(&ir->condition);
 105
 106       ir_constant *const_val = ir->condition->as_constant();
 107       /* If the condition is constant, either remove the condition or
 108        * remove the never-executed assignment.
 109        */
 110       if (const_val) {
 111          if (const_val->value.b[0])
 112             ir->condition = NULL;
 113          else
 114             ir->remove();
 115          this->progress = true;
 116       }
 117    }
 118
 119    /* Don't descend into the LHS because we want it to stay as a
 120     * variable dereference.  FINISHME: We probably should to get array
 121     * indices though.
 122     */
 123    return visit_continue_with_parent;
 124 }
 125
 126 ir_visitor_status
 127 ir_constant_folding_visitor::visit_enter(ir_call *ir)
 128 {
 129    /* Attempt to constant fold parameters */
 130    foreach_two_lists(formal_node, &ir->callee->parameters,
 131                      actual_node, &ir->actual_parameters) {
 132       ir_rvalue *param_rval = (ir_rvalue *) actual_node;
 133       ir_variable *sig_param = (ir_variable *) formal_node;
 134
 135       if (sig_param->data.mode == ir_var_function_in
 136           || sig_param->data.mode == ir_var_const_in) {
 137          ir_rvalue *new_param = param_rval;
 138
 139          handle_rvalue(&new_param);
 140          if (new_param != param_rval) {
 141             param_rval->replace_with(new_param);
 142          }
 143       }
 144    }
 145
 146    /* Next, see if the call can be replaced with an assignment of a constant */
 147    ir_constant *const_val = ir->constant_expression_value();
 148
 149    if (const_val != NULL) {
 150       ir_assignment *assignment =
 151          new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
 152       ir->replace_with(assignment);
 153    }
 154
 155    return visit_continue_with_parent;
 156 }
 157
 158 bool
 159 do_constant_folding(exec_list *instructions)
 160 {
 161    ir_constant_folding_visitor constant_folding;
 162
 163    visit_list_elements(&constant_folding, instructions);
 164
 165    return constant_folding.progress;
 166 }