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      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) {
    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 }
    148