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 "compiler/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_discard *ir);
  54    virtual ir_visitor_status visit_enter(ir_assignment *ir);
  55    virtual ir_visitor_status visit_enter(ir_call *ir);
  56
  57    virtual void handle_rvalue(ir_rvalue **rvalue);
  58
  59    bool progress;
  60 };
  61
  62 } /* unnamed namespace */
  63
  64 void
  65 ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
  66 {
  67    if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
  68       return;
  69
  70    /* Note that we do rvalue visitoring on leaving.  So if an
  71     * expression has a non-constant operand, no need to go looking
  72     * down it to find if it's constant.  This cuts the time of this
  73     * pass down drastically.
  74     */
  75    ir_expression *expr = (*rvalue)->as_expression();
  76    if (expr) {
  77       for (unsigned int i = 0; i < expr->get_num_operands(); i++) {
  78          if (!expr->operands[i]->as_constant())
  79             return;
  80       }
  81    }
  82
  83    /* Ditto for swizzles. */
  84    ir_swizzle *swiz = (*rvalue)->as_swizzle();
  85    if (swiz && !swiz->val->as_constant())
  86       return;
  87
  88    ir_constant *constant = (*rvalue)->constant_expression_value();
  89    if (constant) {
  90       *rvalue = constant;
  91       this->progress = true;
  92    } else {
  93       (*rvalue)->accept(this);
  94    }
  95 }
  96
  97 ir_visitor_status
  98 ir_constant_folding_visitor::visit_enter(ir_discard *ir)
  99 {
 100    if (ir->condition) {
 101       ir->condition->accept(this);
 102       handle_rvalue(&ir->condition);
 103
 104       ir_constant *const_val = ir->condition->as_constant();
 105       /* If the condition is constant, either remove the condition or
 106        * remove the never-executed assignment.
 107        */
 108       if (const_val) {
 109          if (const_val->value.b[0])
 110             ir->condition = NULL;
 111          else
 112             ir->remove();
 113          this->progress = true;
 114       }
 115    }
 116
 117    return visit_continue_with_parent;
 118 }
 119
 120 ir_visitor_status
 121 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
 122 {
 123    ir->rhs->accept(this);
 124    handle_rvalue(&ir->rhs);
 125
 126    if (ir->condition) {
 127       ir->condition->accept(this);
 128       handle_rvalue(&ir->condition);
 129
 130       ir_constant *const_val = ir->condition->as_constant();
 131       /* If the condition is constant, either remove the condition or
 132        * remove the never-executed assignment.
 133        */
 134       if (const_val) {
 135          if (const_val->value.b[0])
 136             ir->condition = NULL;
 137          else
 138             ir->remove();
 139          this->progress = true;
 140       }
 141    }
 142
 143    /* Don't descend into the LHS because we want it to stay as a
 144     * variable dereference.  FINISHME: We probably should to get array
 145     * indices though.
 146     */
 147    return visit_continue_with_parent;
 148 }
 149
 150 ir_visitor_status
 151 ir_constant_folding_visitor::visit_enter(ir_call *ir)
 152 {
 153    /* Attempt to constant fold parameters */
 154    foreach_two_lists(formal_node, &ir->callee->parameters,
 155                      actual_node, &ir->actual_parameters) {
 156       ir_rvalue *param_rval = (ir_rvalue *) actual_node;
 157       ir_variable *sig_param = (ir_variable *) formal_node;
 158
 159       if (sig_param->data.mode == ir_var_function_in
 160           || sig_param->data.mode == ir_var_const_in) {
 161          ir_rvalue *new_param = param_rval;
 162
 163          handle_rvalue(&new_param);
 164          if (new_param != param_rval) {
 165             param_rval->replace_with(new_param);
 166          }
 167       }
 168    }
 169
 170    /* Next, see if the call can be replaced with an assignment of a constant */
 171    ir_constant *const_val = ir->constant_expression_value();
 172
 173    if (const_val != NULL) {
 174       ir_assignment *assignment =
 175          new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
 176       ir->replace_with(assignment);
 177    }
 178
 179    return visit_continue_with_parent;
 180 }
 181
 182 bool
 183 do_constant_folding(exec_list *instructions)
 184 {
 185    ir_constant_folding_visitor constant_folding;
 186
 187    visit_list_elements(&constant_folding, instructions);
 188
 189    return constant_folding.progress;
 190 }