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_if_simplification.cpp
26 *
27 * Moves constant branches of if statements out to the surrounding
28 * instruction stream.
29 */
30
31 #include "ir.h"
32
33 namespace {
34
35 class ir_if_simplification_visitor : public ir_hierarchical_visitor {
36 public:
ir_if_simplification_visitor()37 ir_if_simplification_visitor()
38 {
39 this->made_progress = false;
40 }
41
42 ir_visitor_status visit_leave(ir_if *);
43 ir_visitor_status visit_enter(ir_assignment *);
44
45 bool made_progress;
46 };
47
48 } /* unnamed namespace */
49
50 /* We only care about the top level "if" instructions, so don't
51 * descend into expressions.
52 */
53 ir_visitor_status
visit_enter(ir_assignment * ir)54 ir_if_simplification_visitor::visit_enter(ir_assignment *ir)
55 {
56 (void) ir;
57 return visit_continue_with_parent;
58 }
59
60 bool
do_if_simplification(exec_list * instructions)61 do_if_simplification(exec_list *instructions)
62 {
63 ir_if_simplification_visitor v;
64
65 v.run(instructions);
66 return v.made_progress;
67 }
68
69
70 ir_visitor_status
visit_leave(ir_if * ir)71 ir_if_simplification_visitor::visit_leave(ir_if *ir)
72 {
73 /* If the if statement has nothing on either side, remove it. */
74 if (ir->then_instructions.is_empty() &&
75 ir->else_instructions.is_empty()) {
76 ir->remove();
77 this->made_progress = true;
78 return visit_continue;
79 }
80
81 /* FINISHME: Ideally there would be a way to note that the condition results
82 * FINISHME: in a constant before processing both of the other subtrees.
83 * FINISHME: This can probably be done with some flags, but it would take
84 * FINISHME: some work to get right.
85 */
86 ir_constant *condition_constant = ir->condition->constant_expression_value();
87 if (condition_constant) {
88 /* Move the contents of the one branch of the conditional
89 * that matters out.
90 */
91 if (condition_constant->value.b[0]) {
92 foreach_iter(exec_list_iterator, then_iter, ir->then_instructions) {
93 ir_instruction *then_ir = (ir_instruction *)then_iter.get();
94 ir->insert_before(then_ir);
95 }
96 } else {
97 foreach_iter(exec_list_iterator, else_iter, ir->else_instructions) {
98 ir_instruction *else_ir = (ir_instruction *)else_iter.get();
99 ir->insert_before(else_ir);
100 }
101 }
102 ir->remove();
103 this->made_progress = true;
104 }
105
106 return visit_continue;
107 }
108