neyuki 0.6.1

A small Lua-like scripting language implemented in Rust
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
136
137
138
139
140
141
142
143

//! Copy propagation: uses of a moved variable read the original instead.

use std::collections::HashMap;

use crate::compiler::ir::block::{ControlFlowGraph, IrModule};
use crate::compiler::ir::inst::IrInst;
use crate::compiler::ir::types::IrVar;

pub fn copy_propagation(module: &mut IrModule) {
    let captured = std::collections::HashSet::new();
    propagate_copies_slice(&mut module.main.instructions, &captured);
}

pub fn copy_propagation_cfg(cfg: &mut ControlFlowGraph) -> bool {
    let captured = super::captured_vars(cfg);
    let mut changed = false;
    for block in &mut cfg.blocks {
        if propagate_copies_slice(&mut block.instructions, &captured) {
            changed = true;
        }
        let before_len = block.instructions.len();
        block.instructions.retain(|inst| {
            if let IrInst::Move { dst, src } = inst {
                dst != src
            } else {
                true
            }
        });
        if block.instructions.len() != before_len {
            changed = true;
        }
    }
    changed
}

fn propagate_copies_slice(
    instructions: &mut [IrInst],
    captured: &std::collections::HashSet<IrVar>,
) -> bool {
    let mut copies: HashMap<IrVar, IrVar> = HashMap::new();
    let mut modified = false;

    for inst in instructions.iter_mut() {
        // Resolve uses using current copy map
        let replace_var = |v: &mut IrVar, copies: &HashMap<IrVar, IrVar>| -> bool {
            let mut cur = *v;
            let mut rep = false;
            while let Some(&src) = copies.get(&cur) {
                cur = src;
                rep = true;
            }
            if rep {
                *v = cur;
            }
            rep
        };

        match inst {
            IrInst::Move { src, .. }
            | IrInst::UnOp { src, .. }
            | IrInst::AppendArray { src, .. } => {
                if replace_var(src, &copies) {
                    modified = true;
                }
            }
            IrInst::BinOp { lhs, rhs, .. } => {
                if replace_var(lhs, &copies) {
                    modified = true;
                }
                if replace_var(rhs, &copies) {
                    modified = true;
                }
            }
            IrInst::GetTable { table, key, .. } => {
                if replace_var(table, &copies) {
                    modified = true;
                }
                if replace_var(key, &copies) {
                    modified = true;
                }
            }
            IrInst::SetTable { table, key, val } => {
                if replace_var(table, &copies) {
                    modified = true;
                }
                if replace_var(key, &copies) {
                    modified = true;
                }
                if replace_var(val, &copies) {
                    modified = true;
                }
            }
            IrInst::SetGlobal { src, .. } | IrInst::SetUpval { src, .. } => {
                if replace_var(src, &copies) {
                    modified = true;
                }
            }
            IrInst::Call { callee, args, .. } => {
                if replace_var(callee, &copies) {
                    modified = true;
                }
                for arg in args {
                    if replace_var(arg, &copies) {
                        modified = true;
                    }
                }
            }
            IrInst::Return(vars) => {
                for v in vars {
                    if replace_var(v, &copies) {
                        modified = true;
                    }
                }
            }
            IrInst::JumpIfFalse { cond, .. } => {
                if replace_var(cond, &copies) {
                    modified = true;
                }
            }
            _ => {}
        }

        // Invalidate copies if destination or source is overwritten
        for def in inst.def_vars() {
            copies.remove(&def);
            copies.retain(|_, src| *src != def);
        }

        // Register new copy
        match inst {
            // A captured variable's register is what the closure reads, so
            // neither side of such a copy can be forwarded away.
            IrInst::Move { dst, src }
                if *dst != *src && !captured.contains(dst) && !captured.contains(src) =>
            {
                copies.insert(*dst, *src);
            }
            _ => {}
        }
    }

    modified
}