Sha256: 2de09da660ce6255edac96f26d7cbdd71db0f1c89c29692b320daae1a80d5b4d
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Versions: 25
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Contents
//! A Dead-Code Elimination (DCE) pass.
//!
//! Dead code here means instructions that have no side effects and have no
//! result values used by other instructions.
use crate::cursor::{Cursor, FuncCursor};
use crate::dominator_tree::DominatorTree;
use crate::entity::EntityRef;
use crate::inst_predicates::{any_inst_results_used, has_side_effect};
use crate::ir::Function;
use crate::timing;
/// Perform DCE on `func`.
pub fn do_dce(func: &mut Function, domtree: &DominatorTree) {
let _tt = timing::dce();
debug_assert!(domtree.is_valid());
let mut live = vec![false; func.dfg.num_values()];
for &block in domtree.cfg_postorder() {
let mut pos = FuncCursor::new(func).at_bottom(block);
while let Some(inst) = pos.prev_inst() {
{
if has_side_effect(pos.func, inst)
|| any_inst_results_used(inst, &live, &pos.func.dfg)
{
for arg in pos.func.dfg.inst_values(inst) {
let v = pos.func.dfg.resolve_aliases(arg);
live[v.index()] = true;
}
continue;
}
}
pos.remove_inst();
}
}
}
Version data entries
25 entries across 25 versions & 1 rubygems