waffle/src/cfg/mod.rs

//! Lightweight CFG analyses.

// Borrowed from regalloc2's cfg.rs, which is also Apache-2.0 with
// LLVM exception.

use crate::entity::PerEntity;
use crate::ir::{Block, FunctionBody, Terminator};
use smallvec::SmallVec;

pub mod domtree;
pub mod postorder;

#[derive(Clone, Debug)]
pub struct CFGInfo {
    /// Entry block.
    pub entry: Block,
    /// Predecessors for each block.
    pub block_preds: PerEntity<Block, SmallVec<[Block; 4]>>,
    /// Successors for each block.
    pub block_succs: PerEntity<Block, SmallVec<[Block; 4]>>,
    /// Blocks that end in return.
    pub return_blocks: Vec<Block>,
    /// Postorder traversal of blocks.
    pub postorder: Vec<Block>,
    /// Position of each block in postorder, if reachable.
    pub postorder_pos: PerEntity<Block, Option<usize>>,
    /// Domtree parents, indexed by block.
    pub domtree: PerEntity<Block, Block>,
}

impl CFGInfo {
    pub fn new(f: &FunctionBody) -> CFGInfo {
        let mut block_preds: PerEntity<Block, SmallVec<[Block; 4]>> = PerEntity::default();
        let mut block_succs: PerEntity<Block, SmallVec<[Block; 4]>> = PerEntity::default();
        for (block, block_def) in f.blocks.entries() {
            block_def.terminator.visit_successors(|succ| {
                block_preds[succ].push(block);
                block_succs[block].push(succ);
            });
        }

        let mut return_blocks = vec![];
        for (block_id, block) in f.blocks.entries() {
            if let Terminator::Return { .. } = &block.terminator {
                return_blocks.push(block_id);
            }
        }

        let postorder = postorder::calculate(f.entry, |block| &block_succs[block]);

        let mut postorder_pos = PerEntity::default();
        for (i, block) in postorder.iter().enumerate() {
            postorder_pos[*block] = Some(i);
        }

        let domtree = domtree::calculate(
            |block| &&block_preds[block],
            &postorder[..],
            f.entry,
        );

        CFGInfo {
            entry: f.entry,
            block_preds,
            block_succs,
            return_blocks,
            postorder,
            postorder_pos,
            domtree,
        }
    }

    pub fn dominates(&self, a: Block, b: Block) -> bool {
        domtree::dominates(&self.domtree, a, b)
    }

    pub fn succs(&self, block: Block) -> &[Block] {
        &self.block_succs[block]
    }

    pub fn preds(&self, block: Block) -> &[Block] {
        &self.block_preds[block]
    }

    pub fn pred_count_with_entry(&self, block: Block) -> usize {
        let is_entry = block == self.entry;
        self.preds(block).len() + if is_entry { 1 } else { 0 }
    }

    pub fn succ_count_with_return(&self, block: Block) -> usize {
        let is_return = self.return_blocks.binary_search(&block).is_ok();
        self.succs(block).len() + if is_return { 1 } else { 0 }
    }

    pub fn rpo(&self) -> Vec<Block> {
        self.postorder.iter().cloned().rev().collect()
    }

    pub fn rpo_pos(&self, block: Block) -> Option<usize> {
        self.postorder_pos[block].map(|fwd_pos| self.postorder.len() - 1 - fwd_pos)
    }
}