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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 "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 bool
     65 ir_constant_fold(ir_rvalue **rvalue)
     66 {
     67    if (*rvalue == NULL || (*rvalue)->ir_type == ir_type_constant)
     68       return false;
     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->num_operands; i++) {
     78 	 if (!expr->operands[i]->as_constant())
     79 	    return false;
     80       }
     81    }
     82 
     83    /* Ditto for swizzles. */
     84    ir_swizzle *swiz = (*rvalue)->as_swizzle();
     85    if (swiz && !swiz->val->as_constant())
     86       return false;
     87 
     88    /* Ditto for array dereferences */
     89    ir_dereference_array *array_ref = (*rvalue)->as_dereference_array();
     90    if (array_ref && (!array_ref->array->as_constant() ||
     91                      !array_ref->array_index->as_constant()))
     92       return false;
     93 
     94    /* No constant folding can be performed on variable dereferences.  We need
     95     * to explicitly avoid them, as calling constant_expression_value() on a
     96     * variable dereference will return a clone of var->constant_value.  This
     97     * would make us propagate the value into the tree, which isn't our job.
     98     */
     99    ir_dereference_variable *var_ref = (*rvalue)->as_dereference_variable();
    100    if (var_ref)
    101       return false;
    102 
    103    ir_constant *constant =
    104       (*rvalue)->constant_expression_value(ralloc_parent(*rvalue));
    105    if (constant) {
    106       *rvalue = constant;
    107       return true;
    108    }
    109    return false;
    110 }
    111 
    112 void
    113 ir_constant_folding_visitor::handle_rvalue(ir_rvalue **rvalue)
    114 {
    115    if (ir_constant_fold(rvalue))
    116       this->progress = true;
    117 }
    118 
    119 ir_visitor_status
    120 ir_constant_folding_visitor::visit_enter(ir_discard *ir)
    121 {
    122    if (ir->condition) {
    123       ir->condition->accept(this);
    124       handle_rvalue(&ir->condition);
    125 
    126       ir_constant *const_val = ir->condition->as_constant();
    127       /* If the condition is constant, either remove the condition or
    128        * remove the never-executed assignment.
    129        */
    130       if (const_val) {
    131          if (const_val->value.b[0])
    132             ir->condition = NULL;
    133          else
    134             ir->remove();
    135          this->progress = true;
    136       }
    137    }
    138 
    139    return visit_continue_with_parent;
    140 }
    141 
    142 ir_visitor_status
    143 ir_constant_folding_visitor::visit_enter(ir_assignment *ir)
    144 {
    145    ir->rhs->accept(this);
    146    handle_rvalue(&ir->rhs);
    147 
    148    if (ir->condition) {
    149       ir->condition->accept(this);
    150       handle_rvalue(&ir->condition);
    151 
    152       ir_constant *const_val = ir->condition->as_constant();
    153       /* If the condition is constant, either remove the condition or
    154        * remove the never-executed assignment.
    155        */
    156       if (const_val) {
    157 	 if (const_val->value.b[0])
    158 	    ir->condition = NULL;
    159 	 else
    160 	    ir->remove();
    161 	 this->progress = true;
    162       }
    163    }
    164 
    165    /* Don't descend into the LHS because we want it to stay as a
    166     * variable dereference.  FINISHME: We probably should to get array
    167     * indices though.
    168     */
    169    return visit_continue_with_parent;
    170 }
    171 
    172 ir_visitor_status
    173 ir_constant_folding_visitor::visit_enter(ir_call *ir)
    174 {
    175    /* Attempt to constant fold parameters */
    176    foreach_two_lists(formal_node, &ir->callee->parameters,
    177                      actual_node, &ir->actual_parameters) {
    178       ir_rvalue *param_rval = (ir_rvalue *) actual_node;
    179       ir_variable *sig_param = (ir_variable *) formal_node;
    180 
    181       if (sig_param->data.mode == ir_var_function_in
    182           || sig_param->data.mode == ir_var_const_in) {
    183 	 ir_rvalue *new_param = param_rval;
    184 
    185 	 handle_rvalue(&new_param);
    186 	 if (new_param != param_rval) {
    187 	    param_rval->replace_with(new_param);
    188 	 }
    189       }
    190    }
    191 
    192    /* Next, see if the call can be replaced with an assignment of a constant */
    193    ir_constant *const_val = ir->constant_expression_value(ralloc_parent(ir));
    194 
    195    if (const_val != NULL) {
    196       ir_assignment *assignment =
    197 	 new(ralloc_parent(ir)) ir_assignment(ir->return_deref, const_val);
    198       ir->replace_with(assignment);
    199    }
    200 
    201    return visit_continue_with_parent;
    202 }
    203 
    204 bool
    205 do_constant_folding(exec_list *instructions)
    206 {
    207    ir_constant_folding_visitor constant_folding;
    208 
    209    visit_list_elements(&constant_folding, instructions);
    210 
    211    return constant_folding.progress;
    212 }
    213