cranelift_codegen/
dce.rs

1//! A Dead-Code Elimination (DCE) pass.
2//!
3//! Dead code here means instructions that have no side effects and have no
4//! result values used by other instructions.
5
6use crate::cursor::{Cursor, FuncCursor};
7use crate::dominator_tree::DominatorTree;
8use crate::entity::EntityRef;
9use crate::inst_predicates::{any_inst_results_used, has_side_effect};
10use crate::ir::Function;
11use crate::timing;
12
13/// Perform DCE on `func`.
14pub fn do_dce(func: &mut Function, domtree: &DominatorTree) {
15    let _tt = timing::dce();
16    debug_assert!(domtree.is_valid());
17
18    let mut live = vec![false; func.dfg.num_values()];
19    for &block in domtree.cfg_postorder() {
20        let mut pos = FuncCursor::new(func).at_bottom(block);
21        while let Some(inst) = pos.prev_inst() {
22            {
23                if has_side_effect(pos.func, inst)
24                    || any_inst_results_used(inst, &live, &pos.func.dfg)
25                {
26                    for arg in pos.func.dfg.inst_values(inst) {
27                        let v = pos.func.dfg.resolve_aliases(arg);
28                        live[v.index()] = true;
29                    }
30
31                    continue;
32                }
33            }
34            pos.remove_inst();
35        }
36    }
37}
cranelift_codegen/dce.rs

cranelift_codegen/
dce.rs
