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  1. /*
  2.  * Copyright © 2013 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_flatten_nested_if_blocks.cpp
  26.  *
  27.  * Flattens nested if blocks such as:
  28.  *
  29.  * if (x) {
  30.  *    if (y) {
  31.  *       ...
  32.  *    }
  33.  * }
  34.  *
  35.  * into a single if block with a combined condition:
  36.  *
  37.  * if (x && y) {
  38.  *    ...
  39.  * }
  40.  */
  41.  
  42. #include "ir.h"
  43. #include "ir_builder.h"
  44.  
  45. using namespace ir_builder;
  46.  
  47. namespace {
  48.  
  49. class nested_if_flattener : public ir_hierarchical_visitor {
  50. public:
  51.    nested_if_flattener()
  52.    {
  53.       progress = false;
  54.    }
  55.  
  56.    ir_visitor_status visit_leave(ir_if *);
  57.    ir_visitor_status visit_enter(ir_assignment *);
  58.  
  59.    bool progress;
  60. };
  61.  
  62. } /* unnamed namespace */
  63.  
  64. /* We only care about the top level "if" instructions, so don't
  65.  * descend into expressions.
  66.  */
  67. ir_visitor_status
  68. nested_if_flattener::visit_enter(ir_assignment *ir)
  69. {
  70.    (void) ir;
  71.    return visit_continue_with_parent;
  72. }
  73.  
  74. bool
  75. opt_flatten_nested_if_blocks(exec_list *instructions)
  76. {
  77.    nested_if_flattener v;
  78.  
  79.    v.run(instructions);
  80.    return v.progress;
  81. }
  82.  
  83.  
  84. ir_visitor_status
  85. nested_if_flattener::visit_leave(ir_if *ir)
  86. {
  87.    /* Only handle a single ir_if within the then clause of an ir_if.  No extra
  88.     * instructions, no else clauses, nothing.
  89.     */
  90.    if (ir->then_instructions.is_empty() || !ir->else_instructions.is_empty())
  91.       return visit_continue;
  92.  
  93.    ir_if *inner = ((ir_instruction *) ir->then_instructions.head)->as_if();
  94.    if (!inner || !inner->next->is_tail_sentinel() ||
  95.        !inner->else_instructions.is_empty())
  96.       return visit_continue;
  97.  
  98.    ir->condition = logic_and(ir->condition, inner->condition);
  99.    inner->then_instructions.move_nodes_to(&ir->then_instructions);
  100.  
  101.    progress = true;
  102.    return visit_continue;
  103. }
  104.