neyuki 0.6.1

A small Lua-like scripting language implemented in Rust
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//! The IR optimization passes and their order.

pub mod const_fold;
pub mod copy_prop;
pub mod cse;
pub mod dce;
pub mod inline;
pub mod loop_invariant;
pub mod simplify_cfg;

use std::collections::HashSet;

use crate::compiler::ir::block::ControlFlowGraph;
use crate::compiler::ir::dom::DominatorTree;
use crate::compiler::ir::inst::IrInst;
use crate::compiler::ir::types::IrVar;

pub use crate::compiler::value_tracking::value_tracking_cfg;
pub use const_fold::constant_propagation;
pub use copy_prop::{copy_propagation, copy_propagation_cfg};
pub use cse::{common_subexpression_elimination, common_subexpression_elimination_cfg};
pub use dce::{dead_code_elimination, dead_code_elimination_cfg};
pub use inline::inline_functions;
pub use loop_invariant::loop_invariant_code_motion;
pub use simplify_cfg::simplify_cfg;

/// The variables nested functions capture. A closure holds the register of
/// each captured variable, not a snapshot of its value, so these are aliased
/// from outside the instruction stream: rewriting or dropping a write to one
/// would change what the closure sees. Passes leave them alone.
pub fn captured_vars(cfg: &ControlFlowGraph) -> HashSet<IrVar> {
    let mut captured = HashSet::new();
    for block in &cfg.blocks {
        for inst in &block.instructions {
            if let IrInst::Closure { captures, .. } = inst {
                captured.extend(captures.iter().flatten().copied());
            }
        }
    }
    captured
}

/// Fixpoint optimization driver for CFG.
/// Iteratively executes optimization passes in sequence until the CFG converges
/// to a fixed point (no further changes are made), bounded by MAX_FIXPOINT_ROUNDS.
pub fn optimize_cfg(cfg: &mut ControlFlowGraph) {
    const MAX_FIXPOINT_ROUNDS: usize = 16;

    for _ in 0..MAX_FIXPOINT_ROUNDS {
        let mut changed = false;

        // 1. Dominator-based Loop Invariant Code Motion
        let dom = DominatorTree::build(cfg);
        if loop_invariant_code_motion(cfg, &dom) {
            changed = true;
        }

        // 2. Common Subexpression Elimination
        if common_subexpression_elimination_cfg(cfg) {
            changed = true;
        }

        // 3. Copy Propagation
        if copy_propagation_cfg(cfg) {
            changed = true;
        }

        // 4. Value Tracking and Constant / Range Propagation
        if value_tracking_cfg(cfg) {
            changed = true;
        }

        // 5. Dead Code Elimination
        if dead_code_elimination_cfg(cfg) {
            changed = true;
        }

        // 6. CFG Simplification (pruning unreachable, collapsing jumps, merging blocks)
        if simplify_cfg(cfg) {
            changed = true;
        }

        if !changed {
            break;
        }
    }
}