feat(ssa): Basic control dependent LICM

compiler/noirc_evaluator/src/ssa/ir/cfg.rs

@@ -89,10 +89,6 @@ impl ControlFlowGraph {
     /// Add a directed edge making `from` a predecessor of `to`.
     fn add_edge(&mut self, from: BasicBlockId, to: BasicBlockId) {
         let predecessor_node = self.data.entry(from).or_default();
-        assert!(
-            predecessor_node.successors.len() < 2,
-            "ICE: A cfg node cannot have more than two successors"
-        );
         predecessor_node.successors.insert(to);
         let successor_node = self.data.entry(to).or_default();
         successor_node.predecessors.insert(from);
@@ -125,7 +121,6 @@ impl ControlFlowGraph {
     }
 
     /// Reverse the control flow graph
-    #[cfg(test)]
     pub(crate) fn reverse(&self) -> Self {
         let mut reversed_cfg = ControlFlowGraph::default();
 

compiler/noirc_evaluator/src/ssa/ir/dom.rs

@@ -178,10 +178,10 @@ impl DominatorTree {
     /// "Simple, Fast Dominator Algorithm."
     fn compute_dominator_tree(&mut self, cfg: &ControlFlowGraph, post_order: &PostOrder) {
         // We'll be iterating over a reverse post-order of the CFG, skipping the entry block.
-        let (entry_block_id, entry_free_post_order) = post_order
-            .as_slice()
-            .split_last()
-            .expect("ICE: functions always have at least one block");
+        let Some((entry_block_id, entry_free_post_order)) = post_order.as_slice().split_last()
+        else {
+            return;
+        };
 
         // Do a first pass where we assign reverse post-order indices to all reachable nodes. The
         // entry block will be the only node with no immediate dominator.