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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 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->mode == ir_var_in || sig_param->mode == ir_var_const_in) {
    131 	 ir_rvalue *new_param = param_rval;
    132 
    133 	 handle_rvalue(&new_param);
    134 	 if (new_param != param_rval) {
    135 	    param_rval->replace_with(new_param);
    136 	 }
    137       }
    138       sig_iter.next();
    139    }
    140 
    141    /* Next, see if the call can be replaced with an assignment of a constant */
    142    ir_constant *const_val = ir->constant_expression_value();
    143 
    144    if (const_val != NULL) {
    145       ir_assignment *assignment =
    146 	 new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
    147       ir->replace_with(assignment);
    148    }
    149 
    150    return visit_continue_with_parent;
    151 }
    152 
    153 bool
    154 do_constant_folding(exec_list *instructions)
    155 {
    156    ir_constant_folding_visitor constant_folding;
    157 
    158    visit_list_elements(&constant_folding, instructions);
    159 
    160    return constant_folding.progress;
    161 }
    162