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      1 /*
      2  * Copyright  2016 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 propagate_invariance.cpp
     26  * Propagate the "invariant" and "precise" qualifiers to variables used to
     27  * compute invariant or precise values.
     28  *
     29  * The GLSL spec (depending on what version you read) says, among the
     30  * conditions for getting bit-for-bit the same values on an invariant output:
     31  *
     32  *    "All operations in the consuming expressions and any intermediate
     33  *    expressions must be the same, with the same order of operands and same
     34  *    associativity, to give the same order of evaluation."
     35  *
     36  * This effectively means that if a variable is used to compute an invariant
     37  * value then that variable becomes invariant.  The same should apply to the
     38  * "precise" qualifier.
     39  */
     40 
     41 #include "ir.h"
     42 #include "ir_visitor.h"
     43 #include "ir_rvalue_visitor.h"
     44 #include "ir_optimization.h"
     45 #include "compiler/glsl_types.h"
     46 
     47 namespace {
     48 
     49 class ir_invariance_propagation_visitor : public ir_hierarchical_visitor {
     50 public:
     51    ir_invariance_propagation_visitor()
     52    {
     53       this->progress = false;
     54       this->dst_var = NULL;
     55    }
     56 
     57    virtual ~ir_invariance_propagation_visitor()
     58    {
     59       /* empty */
     60    }
     61 
     62    virtual ir_visitor_status visit_enter(ir_assignment *ir);
     63    virtual ir_visitor_status visit_leave(ir_assignment *ir);
     64    virtual ir_visitor_status visit(ir_dereference_variable *ir);
     65 
     66    ir_variable *dst_var;
     67    bool progress;
     68 };
     69 
     70 } /* unnamed namespace */
     71 
     72 ir_visitor_status
     73 ir_invariance_propagation_visitor::visit_enter(ir_assignment *ir)
     74 {
     75    assert(this->dst_var == NULL);
     76    ir_variable *var = ir->lhs->variable_referenced();
     77    if (var->data.invariant || var->data.precise) {
     78       this->dst_var = var;
     79       return visit_continue;
     80    } else {
     81       return visit_continue_with_parent;
     82    }
     83 }
     84 
     85 ir_visitor_status
     86 ir_invariance_propagation_visitor::visit_leave(ir_assignment *)
     87 {
     88    this->dst_var = NULL;
     89 
     90    return visit_continue;
     91 }
     92 
     93 ir_visitor_status
     94 ir_invariance_propagation_visitor::visit(ir_dereference_variable *ir)
     95 {
     96    if (this->dst_var == NULL)
     97       return visit_continue;
     98 
     99    if (this->dst_var->data.invariant) {
    100       if (!ir->var->data.invariant)
    101          this->progress = true;
    102 
    103       ir->var->data.invariant = true;
    104    }
    105 
    106    if (this->dst_var->data.precise) {
    107       if (!ir->var->data.precise)
    108          this->progress = true;
    109 
    110       ir->var->data.precise = true;
    111    }
    112 
    113    return visit_continue;
    114 }
    115 
    116 void
    117 propagate_invariance(exec_list *instructions)
    118 {
    119    ir_invariance_propagation_visitor visitor;
    120 
    121    do {
    122       visitor.progress = false;
    123       visit_list_elements(&visitor, instructions);
    124    } while (visitor.progress);
    125 }
    126