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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_variable.cpp
     26  *
     27  * Marks variables assigned a single constant value over the course
     28  * of the program as constant.
     29  *
     30  * The goal here is to trigger further constant folding and then dead
     31  * code elimination.  This is common with vector/matrix constructors
     32  * and calls to builtin functions.
     33  */
     34 
     35 #include "ir.h"
     36 #include "ir_visitor.h"
     37 #include "ir_optimization.h"
     38 #include "glsl_types.h"
     39 
     40 namespace {
     41 
     42 struct assignment_entry {
     43    exec_node link;
     44    int assignment_count;
     45    ir_variable *var;
     46    ir_constant *constval;
     47    bool our_scope;
     48 };
     49 
     50 class ir_constant_variable_visitor : public ir_hierarchical_visitor {
     51 public:
     52    virtual ir_visitor_status visit_enter(ir_dereference_variable *);
     53    virtual ir_visitor_status visit(ir_variable *);
     54    virtual ir_visitor_status visit_enter(ir_assignment *);
     55    virtual ir_visitor_status visit_enter(ir_call *);
     56 
     57    exec_list list;
     58 };
     59 
     60 } /* unnamed namespace */
     61 
     62 static struct assignment_entry *
     63 get_assignment_entry(ir_variable *var, exec_list *list)
     64 {
     65    struct assignment_entry *entry;
     66 
     67    foreach_list_typed(struct assignment_entry, entry, link, list) {
     68       if (entry->var == var)
     69 	 return entry;
     70    }
     71 
     72    entry = (struct assignment_entry *)calloc(1, sizeof(*entry));
     73    entry->var = var;
     74    list->push_head(&entry->link);
     75    return entry;
     76 }
     77 
     78 ir_visitor_status
     79 ir_constant_variable_visitor::visit(ir_variable *ir)
     80 {
     81    struct assignment_entry *entry = get_assignment_entry(ir, &this->list);
     82    entry->our_scope = true;
     83    return visit_continue;
     84 }
     85 
     86 /* Skip derefs of variables so that we can detect declarations. */
     87 ir_visitor_status
     88 ir_constant_variable_visitor::visit_enter(ir_dereference_variable *ir)
     89 {
     90    (void)ir;
     91    return visit_continue_with_parent;
     92 }
     93 
     94 ir_visitor_status
     95 ir_constant_variable_visitor::visit_enter(ir_assignment *ir)
     96 {
     97    ir_constant *constval;
     98    struct assignment_entry *entry;
     99 
    100    entry = get_assignment_entry(ir->lhs->variable_referenced(), &this->list);
    101    assert(entry);
    102    entry->assignment_count++;
    103 
    104    /* If it's already constant, don't do the work. */
    105    if (entry->var->constant_value)
    106       return visit_continue;
    107 
    108    /* OK, now find if we actually have all the right conditions for
    109     * this to be a constant value assigned to the var.
    110     */
    111    if (ir->condition)
    112       return visit_continue;
    113 
    114    ir_variable *var = ir->whole_variable_written();
    115    if (!var)
    116       return visit_continue;
    117 
    118    constval = ir->rhs->constant_expression_value();
    119    if (!constval)
    120       return visit_continue;
    121 
    122    /* Mark this entry as having a constant assignment (if the
    123     * assignment count doesn't go >1).  do_constant_variable will fix
    124     * up the variable with the constant value later.
    125     */
    126    entry->constval = constval;
    127 
    128    return visit_continue;
    129 }
    130 
    131 ir_visitor_status
    132 ir_constant_variable_visitor::visit_enter(ir_call *ir)
    133 {
    134    /* Mark any out parameters as assigned to */
    135    exec_list_iterator sig_iter = ir->callee->parameters.iterator();
    136    foreach_iter(exec_list_iterator, iter, *ir) {
    137       ir_rvalue *param_rval = (ir_rvalue *)iter.get();
    138       ir_variable *param = (ir_variable *)sig_iter.get();
    139 
    140       if (param->mode == ir_var_out ||
    141 	  param->mode == ir_var_inout) {
    142 	 ir_variable *var = param_rval->variable_referenced();
    143 	 struct assignment_entry *entry;
    144 
    145 	 assert(var);
    146 	 entry = get_assignment_entry(var, &this->list);
    147 	 entry->assignment_count++;
    148       }
    149       sig_iter.next();
    150    }
    151 
    152    /* Mark the return storage as having been assigned to */
    153    if (ir->return_deref != NULL) {
    154       ir_variable *var = ir->return_deref->variable_referenced();
    155       struct assignment_entry *entry;
    156 
    157       assert(var);
    158       entry = get_assignment_entry(var, &this->list);
    159       entry->assignment_count++;
    160    }
    161 
    162    return visit_continue;
    163 }
    164 
    165 /**
    166  * Does a copy propagation pass on the code present in the instruction stream.
    167  */
    168 bool
    169 do_constant_variable(exec_list *instructions)
    170 {
    171    bool progress = false;
    172    ir_constant_variable_visitor v;
    173 
    174    v.run(instructions);
    175 
    176    while (!v.list.is_empty()) {
    177 
    178       struct assignment_entry *entry;
    179       entry = exec_node_data(struct assignment_entry, v.list.head, link);
    180 
    181       if (entry->assignment_count == 1 && entry->constval && entry->our_scope) {
    182 	 entry->var->constant_value = entry->constval;
    183 	 progress = true;
    184       }
    185       entry->link.remove();
    186       free(entry);
    187    }
    188 
    189    return progress;
    190 }
    191 
    192 bool
    193 do_constant_variable_unlinked(exec_list *instructions)
    194 {
    195    bool progress = false;
    196 
    197    foreach_iter(exec_list_iterator, iter, *instructions) {
    198       ir_instruction *ir = (ir_instruction *)iter.get();
    199       ir_function *f = ir->as_function();
    200       if (f) {
    201 	 foreach_iter(exec_list_iterator, sigiter, *f) {
    202 	    ir_function_signature *sig =
    203 	       (ir_function_signature *) sigiter.get();
    204 	    if (do_constant_variable(&sig->body))
    205 	       progress = true;
    206 	 }
    207       }
    208    }
    209 
    210    return progress;
    211 }
    212