1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
|
// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use rustc::middle::const_eval::ConstVal;
use rustc::mir::repr::*;
use std::mem;
use transform::util;
use transform::MirPass;
pub struct SimplifyCfg;
impl SimplifyCfg {
pub fn new() -> SimplifyCfg {
SimplifyCfg
}
fn remove_dead_blocks(&self, mir: &mut Mir) {
let mut seen = vec![false; mir.basic_blocks.len()];
// These blocks are always required.
seen[START_BLOCK.index()] = true;
seen[END_BLOCK.index()] = true;
seen[DIVERGE_BLOCK.index()] = true;
let mut worklist = vec![START_BLOCK];
while let Some(bb) = worklist.pop() {
for succ in mir.basic_block_data(bb).terminator.successors() {
if !seen[succ.index()] {
seen[succ.index()] = true;
worklist.push(*succ);
}
}
}
util::retain_basic_blocks(mir, &seen);
}
fn remove_goto_chains(&self, mir: &mut Mir) -> bool {
// Find the target at the end of the jump chain, return None if there is a loop
fn final_target(mir: &Mir, mut target: BasicBlock) -> Option<BasicBlock> {
// Keep track of already seen blocks to detect loops
let mut seen: Vec<BasicBlock> = Vec::with_capacity(8);
while mir.basic_block_data(target).statements.is_empty() {
match mir.basic_block_data(target).terminator {
Terminator::Goto { target: next } => {
if seen.contains(&next) {
return None;
}
seen.push(next);
target = next;
}
_ => break
}
}
Some(target)
}
let mut changed = false;
for bb in mir.all_basic_blocks() {
// Temporarily swap out the terminator we're modifying to keep borrowck happy
let mut terminator = Terminator::Diverge;
mem::swap(&mut terminator, &mut mir.basic_block_data_mut(bb).terminator);
for target in terminator.successors_mut() {
let new_target = match final_target(mir, *target) {
Some(new_target) => new_target,
None if mir.basic_block_data(bb).statements.is_empty() => bb,
None => continue
};
changed |= *target != new_target;
*target = new_target;
}
mir.basic_block_data_mut(bb).terminator = terminator;
}
changed
}
fn simplify_branches(&self, mir: &mut Mir) -> bool {
let mut changed = false;
for bb in mir.all_basic_blocks() {
// Temporarily swap out the terminator we're modifying to keep borrowck happy
let mut terminator = Terminator::Diverge;
mem::swap(&mut terminator, &mut mir.basic_block_data_mut(bb).terminator);
mir.basic_block_data_mut(bb).terminator = match terminator {
Terminator::If { ref targets, .. } if targets[0] == targets[1] => {
changed = true;
Terminator::Goto { target: targets[0] }
}
Terminator::If { ref targets, cond: Operand::Constant(Constant {
literal: Literal::Value {
value: ConstVal::Bool(cond)
}, ..
}) } => {
changed = true;
let target_idx = if cond { 0 } else { 1 };
Terminator::Goto { target: targets[target_idx] }
}
Terminator::SwitchInt { ref targets, .. } if targets.len() == 1 => {
Terminator::Goto { target: targets[0] }
}
_ => terminator
}
}
changed
}
}
impl<'tcx> MirPass<'tcx> for SimplifyCfg {
fn run_on_mir(&mut self, mir: &mut Mir<'tcx>) {
let mut changed = true;
while changed {
changed = self.simplify_branches(mir);
changed |= self.remove_goto_chains(mir);
self.remove_dead_blocks(mir);
}
// FIXME: Should probably be moved into some kind of pass manager
mir.basic_blocks.shrink_to_fit();
}
}
|
