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| 4358 | Serge | 1 | /* |
| 2 | * Copyright © 2010 Intel Corporation |
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| 3 | * |
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| 4 | * Permission is hereby granted, free of charge, to any person obtaining a |
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| 5 | * copy of this software and associated documentation files (the "Software"), |
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| 6 | * to deal in the Software without restriction, including without limitation |
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| 7 | * the rights to use, copy, modify, merge, publish, distribute, sublicense, |
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| 8 | * and/or sell copies of the Software, and to permit persons to whom the |
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| 9 | * Software is furnished to do so, subject to the following conditions: |
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| 10 | * |
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| 11 | * The above copyright notice and this permission notice (including the next |
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| 12 | * paragraph) shall be included in all copies or substantial portions of the |
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| 13 | * Software. |
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| 14 | * |
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| 15 | * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR |
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| 16 | * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, |
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| 17 | * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL |
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| 18 | * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER |
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| 19 | * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING |
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| 20 | * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER |
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| 21 | * DEALINGS IN THE SOFTWARE. |
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| 22 | */ |
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| 23 | |||
| 24 | /** |
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| 25 | * \file opt_if_simplification.cpp |
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| 26 | * |
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| 27 | * Moves constant branches of if statements out to the surrounding |
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| 28 | * instruction stream, and inverts if conditionals to avoid empty |
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| 29 | * "then" blocks. |
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| 30 | */ |
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| 31 | |||
| 32 | #include "ir.h" |
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| 33 | |||
| 34 | namespace { |
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| 35 | |||
| 36 | class ir_if_simplification_visitor : public ir_hierarchical_visitor { |
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| 37 | public: |
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| 38 | ir_if_simplification_visitor() |
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| 39 | { |
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| 40 | this->made_progress = false; |
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| 41 | } |
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| 42 | |||
| 43 | ir_visitor_status visit_leave(ir_if *); |
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| 44 | ir_visitor_status visit_enter(ir_assignment *); |
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| 45 | |||
| 46 | bool made_progress; |
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| 47 | }; |
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| 48 | |||
| 49 | } /* unnamed namespace */ |
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| 50 | |||
| 51 | /* We only care about the top level "if" instructions, so don't |
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| 52 | * descend into expressions. |
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| 53 | */ |
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| 54 | ir_visitor_status |
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| 55 | ir_if_simplification_visitor::visit_enter(ir_assignment *ir) |
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| 56 | { |
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| 57 | (void) ir; |
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| 58 | return visit_continue_with_parent; |
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| 59 | } |
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| 60 | |||
| 61 | bool |
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| 62 | do_if_simplification(exec_list *instructions) |
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| 63 | { |
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| 64 | ir_if_simplification_visitor v; |
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| 65 | |||
| 66 | v.run(instructions); |
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| 67 | return v.made_progress; |
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| 68 | } |
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| 69 | |||
| 70 | |||
| 71 | ir_visitor_status |
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| 72 | ir_if_simplification_visitor::visit_leave(ir_if *ir) |
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| 73 | { |
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| 74 | /* If the if statement has nothing on either side, remove it. */ |
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| 75 | if (ir->then_instructions.is_empty() && |
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| 76 | ir->else_instructions.is_empty()) { |
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| 77 | ir->remove(); |
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| 78 | this->made_progress = true; |
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| 79 | return visit_continue; |
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| 80 | } |
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| 81 | |||
| 82 | /* FINISHME: Ideally there would be a way to note that the condition results |
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| 83 | * FINISHME: in a constant before processing both of the other subtrees. |
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| 84 | * FINISHME: This can probably be done with some flags, but it would take |
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| 85 | * FINISHME: some work to get right. |
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| 86 | */ |
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| 87 | ir_constant *condition_constant = ir->condition->constant_expression_value(); |
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| 88 | if (condition_constant) { |
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| 89 | /* Move the contents of the one branch of the conditional |
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| 90 | * that matters out. |
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| 91 | */ |
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| 92 | if (condition_constant->value.b[0]) { |
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| 93 | foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) { |
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| 94 | ir_instruction *then_ir = (ir_instruction *)then_iter.get(); |
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| 95 | ir->insert_before(then_ir); |
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| 96 | } |
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| 97 | } else { |
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| 98 | foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) { |
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| 99 | ir_instruction *else_ir = (ir_instruction *)else_iter.get(); |
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| 100 | ir->insert_before(else_ir); |
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| 101 | } |
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| 102 | } |
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| 103 | ir->remove(); |
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| 104 | this->made_progress = true; |
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| 105 | return visit_continue; |
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| 106 | } |
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| 107 | |||
| 108 | /* Turn: |
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| 109 | * |
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| 110 | * if (cond) { |
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| 111 | * } else { |
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| 112 | * do_work(); |
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| 113 | * } |
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| 114 | * |
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| 115 | * into : |
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| 116 | * |
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| 117 | * if (!cond) |
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| 118 | * do_work(); |
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| 119 | * |
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| 120 | * which avoids control flow for "else" (which is usually more |
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| 121 | * expensive than normal operations), and the "not" can usually be |
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| 122 | * folded into the generation of "cond" anyway. |
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| 123 | */ |
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| 124 | if (ir->then_instructions.is_empty()) { |
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| 125 | ir->condition = new(ralloc_parent(ir->condition)) |
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| 126 | ir_expression(ir_unop_logic_not, ir->condition); |
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| 127 | ir->else_instructions.move_nodes_to(&ir->then_instructions); |
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| 128 | this->made_progress = true; |
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| 129 | } |
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| 130 | |||
| 131 | return visit_continue; |
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| 132 | } |