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_redundant_jumps.cpp
26 * Remove certain types of redundant jumps
27 */
28
29#include "ir.h"
30
31namespace {
32
33class redundant_jumps_visitor : public ir_hierarchical_visitor {
34public:
35   redundant_jumps_visitor()
36   {
37      this->progress = false;
38   }
39
40   virtual ir_visitor_status visit_leave(ir_if *);
41   virtual ir_visitor_status visit_leave(ir_loop *);
42   virtual ir_visitor_status visit_enter(ir_assignment *);
43
44   bool progress;
45};
46
47} /* unnamed namespace */
48
49/* We only care about the top level instructions, so don't descend
50 * into expressions.
51 */
52ir_visitor_status
53redundant_jumps_visitor::visit_enter(ir_assignment *ir)
54{
55   return visit_continue_with_parent;
56}
57
58ir_visitor_status
59redundant_jumps_visitor::visit_leave(ir_if *ir)
60{
61   /* If the last instruction in both branches is a 'break' or a 'continue',
62    * pull it out of the branches and insert it after the if-statment.  Note
63    * that both must be the same type (either 'break' or 'continue').
64    */
65   ir_instruction *const last_then =
66      (ir_instruction *) ir->then_instructions.get_tail();
67   ir_instruction *const last_else =
68      (ir_instruction *) ir->else_instructions.get_tail();
69
70   if ((last_then == NULL) || (last_else == NULL))
71      return visit_continue;
72
73   if ((last_then->ir_type != ir_type_loop_jump)
74       || (last_else->ir_type != ir_type_loop_jump))
75      return visit_continue;
76
77   ir_loop_jump *const then_jump = (ir_loop_jump *) last_then;
78   ir_loop_jump *const else_jump = (ir_loop_jump *) last_else;
79
80   if (then_jump->mode != else_jump->mode)
81      return visit_continue;
82
83   then_jump->remove();
84   else_jump->remove();
85   this->progress = true;
86
87   ir->insert_after(then_jump);
88
89   /* If both branchs of the if-statement are now empty, remove the
90    * if-statement.
91    */
92   if (ir->then_instructions.is_empty() && ir->else_instructions.is_empty())
93      ir->remove();
94
95   return visit_continue;
96}
97
98
99ir_visitor_status
100redundant_jumps_visitor::visit_leave(ir_loop *ir)
101{
102   /* If the last instruction of a loop body is a 'continue', remove it.
103    */
104   ir_instruction *const last =
105      (ir_instruction *) ir->body_instructions.get_tail();
106
107   if (last && (last->ir_type == ir_type_loop_jump)
108       && (((ir_loop_jump *) last)->mode == ir_loop_jump::jump_continue)) {
109      last->remove();
110      this->progress = true;
111   }
112
113   return visit_continue;
114}
115
116
117bool
118optimize_redundant_jumps(exec_list *instructions)
119{
120   redundant_jumps_visitor v;
121
122   v.run(instructions);
123   return v.progress;
124}
125