feat: compute dominance frontiers

crates/jcc_backend/src/ir/analysis/cfg.rs

@@ -5,42 +5,41 @@ use jcc_entity::{EntitySlice, SecondaryMap, SlicePool};
 #[derive(Default)]
 pub struct ControlFlowGraph {
     pool: SlicePool<Block>,
-    degree: SecondaryMap<Block, u32>,
+    in_degree: SecondaryMap<Block, u32>,
     preds: SecondaryMap<Block, EntitySlice<Block>>,
 }
 
 impl ControlFlowGraph {
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    pub fn preds(&self, block: Block) -> impl IntoIterator<Item = Block> + '_ {
+    pub fn preds(&self, block: Block) -> impl Iterator<Item = Block> + '_ {
         self.pool[self.preds[block]].iter().copied()
     }
 
     pub fn compute(&mut self, prog: &Program, order: &Order) {
         self.pool.clear();
+
         for data in prog.functions.values() {
             if let Some(entry) = data.entry {
                 // Compute degree of each block.
                 for block in order.rpo(entry) {
                     for succ in prog.blocks[block].term.successors() {
-                        self.degree[succ] += 1;
+                        self.in_degree[succ] += 1;
                     }
                 }
 
                 // Allocate space for predecessors of each block.
                 for block in order.rpo(entry) {
-                    let degree = self.degree[block] as usize;
+                    let degree = self.in_degree[block] as usize;
                     self.preds[block] = self.pool.extend(std::iter::repeat_n(block, degree));
                 }
 
                 // Fill predecessors of each block.
                 for block in order.rpo(entry) {
                     for succ in prog.blocks[block].term.successors() {
-                        let idx = (self.degree[succ] - 1) as usize;
-                        self.pool[self.preds[succ]][idx] = block;
-                        self.degree[succ] = idx as u32;
+                        let idx = self.in_degree[succ] - 1;
+
+                        self.in_degree[succ] = idx;
+                        let slice = self.preds[succ];
+                        self.pool[slice][idx as usize] = block;
                     }
                 }
             }