leo_passes/dead_code_elimination/
mod.rs

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
// Copyright (C) 2019-2025 Provable Inc.
// This file is part of the Leo library.

// The Leo library is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// The Leo library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with the Leo library. If not, see <https://www.gnu.org/licenses/>.

//! The Dead Code Elimination pass traverses the AST and eliminates unused code,
//! specifically assignment statements, within the boundary of `transition`s and `function`s.
//! The pass is run after the Function Inlining pass.
//!
//! See https://en.wikipedia.org/wiki/Dead-code_elimination for more information.
//!
//! Consider the following flattened Leo code.
//! ```leo
//! function main(flag: u8, value: u8) -> u8 {
//!     $var$0 = flag == 0u8;
//!     $var$4$5 = value * value;
//!     $var$1 = $var$4$5;
//!     value$2 = $var$1;
//!     value$3 = $var$0 ? value$2 : value;
//!     value$6 = $var$1 * $var$1;
//!     return value$3;
//! }
//! ```
//!
//! The dead code elimination pass produces the following code.
//! ```leo
//! function main(flag: u8, value: u8) -> u8 {
//!     $var$0 = flag == 0u8;
//!     $var$4$5 = value * value;
//!     $var$1 = $var$4$5;
//!     value$2 = $var$1;
//!     value$3 = $var$0 ? value$2 : value;
//!     return value$3;
//! }
//! ```
//! Note this pass relies on the following invariants:
//! - No shadowing for all variables, struct names, function names, etc.
//! - Unique variable names (provided by SSA)
//! - Flattened code (provided by the flattening pass)

mod eliminate_expression;

mod eliminate_statement;

mod eliminate_program;

pub mod dead_code_eliminator;
pub use dead_code_eliminator::*;

use crate::Pass;

use leo_ast::{Ast, NodeBuilder, ProgramReconstructor};
use leo_errors::Result;

impl<'a> Pass for DeadCodeEliminator<'a> {
    type Input = (Ast, &'a NodeBuilder);
    type Output = Result<Ast>;

    fn do_pass((ast, node_builder): Self::Input) -> Self::Output {
        let mut reconstructor = DeadCodeEliminator::new(node_builder);
        let program = reconstructor.reconstruct_program(ast.into_repr());

        Ok(Ast::new(program))
    }
}