Method compute_idom

cranelift/codegen/src/dominator_tree/simple.rs:309–328

Compute the immediate dominator for `block` using the current `idom` states for the reachable nodes.

(&self, block: Block, cfg: &ControlFlowGraph)

    // Compute the immediate dominator for `block` using the current `idom` states for the reachable
    // nodes.
    fn compute_idom(&self, block: Block, cfg: &ControlFlowGraph) -> Block {
        // Get an iterator with just the reachable, already visited predecessors to `block`.
        // Note that during the first pass, `rpo_number` is 1 for reachable blocks that haven't
        // been visited yet, 0 for unreachable blocks.
        let mut reachable_preds = cfg
            .pred_iter(block)
            .filter(|&BlockPredecessor { block: pred, .. }| self.nodes[pred].rpo_number > 1)
            .map(|pred| pred.block);

        // The RPO must visit at least one predecessor before this node.
        let mut idom = reachable_preds
            .next()
            .expect("block node must have one reachable predecessor");

        for pred in reachable_preds {
            idom = self.common_dominator(idom, pred);
        }

        idom
    }
}

#[cfg(test)]