src/glsl/ir_if_return.cpp

   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 ir_if_return.cpp
  26  *
  27  * If a function includes an if statement that returns from both
  28  * branches, then make the branches write the return val to a temp and
  29  * return the temp after the if statement.
  30  *
  31  * This allows inlinining in the common case of short functions that
  32  * return one of two values based on a condition.  This helps on
  33  * hardware with no branching support, and may even be a useful
  34  * transform on hardware supporting control flow by masked returns
  35  * with normal returns.
  36  */
  37
  38 #include "ir.h"
  39
  40 class ir_if_return_visitor : public ir_hierarchical_visitor {
  41 public:
  42    ir_if_return_visitor()
  43    {
  44       this->progress = false;
  45    }
  46
  47    ir_visitor_status visit_enter(ir_if *);
  48
  49    bool progress;
  50 };
  51
  52 bool
  53 do_if_return(exec_list *instructions)
  54 {
  55    ir_if_return_visitor v;
  56
  57    visit_list_elements(&v, instructions);
  58
  59    return v.progress;
  60 }
  61
  62
  63 ir_visitor_status
  64 ir_if_return_visitor::visit_enter(ir_if *ir)
  65 {
  66    ir_return *then_return = NULL;
  67    ir_return *else_return = NULL;
  68
  69    /* Try to find a return statement on both sides. */
  70    foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
  71       ir_instruction *then_ir = (ir_instruction *)then_iter.get();
  72       then_return = then_ir->as_return();
  73       if (then_return)
  74          break;
  75    }
  76    if (!then_return)
  77       return visit_continue;
  78
  79    foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
  80       ir_instruction *else_ir = (ir_instruction *)else_iter.get();
  81       else_return = else_ir->as_return();
  82       if (else_return)
  83          break;
  84    }
  85    if (!else_return)
  86       return visit_continue;
  87
  88    /* Trim off any trailing instructions after the return statements
  89     * on both sides.
  90     */
  91    while (then_return->get_next()->get_next())
  92       ((ir_instruction *)then_return->get_next())->remove();
  93    while (else_return->get_next()->get_next())
  94       ((ir_instruction *)else_return->get_next())->remove();
  95
  96    this->progress = true;
  97
  98    if (!then_return->value) {
  99       then_return->remove();
 100       else_return->remove();
 101       ir->insert_after(new(ir) ir_return(NULL));
 102    } else {
 103       ir_assignment *assign;
 104       ir_variable *new_var = new(ir) ir_variable(then_return->value->type,
 105                                                  "if_return_tmp",
 106                                                  ir_var_temporary);
 107       ir->insert_before(new_var);
 108
 109       assign = new(ir) ir_assignment(new(ir) ir_dereference_variable(new_var),
 110                                      then_return->value, NULL);
 111       then_return->replace_with(assign);
 112
 113       assign = new(ir) ir_assignment(new(ir) ir_dereference_variable(new_var),
 114                                      else_return->value, NULL);
 115       else_return->replace_with(assign);
 116
 117       ir_dereference_variable *deref = new(ir) ir_dereference_variable(new_var);
 118       ir->insert_after(new(ir) ir_return(deref));
 119    }
 120
 121    return visit_continue;
 122 }