Possible fix for reduce cycles

• Don't go through phis outside of a fork join when calculating reduce cycles.

hercules_ir/src/loops.rs

@@ -233,14 +233,21 @@ fn loop_reachability_helper(
 pub fn reduce_cycles(
     function: &Function,
     def_use: &ImmutableDefUseMap,
+    fork_join_map: &HashMap<NodeID, NodeID>,
+    fork_join_nest: &HashMap<NodeID, Vec<NodeID>>,
 ) -> HashMap<NodeID, HashSet<NodeID>> {
     let reduces = (0..function.nodes.len())
         .filter(|idx| function.nodes[*idx].is_reduce())
         .map(NodeID::new);
     let mut result = HashMap::new();
+    let join_fork_map: HashMap<NodeID, NodeID> = fork_join_map
+        .into_iter()
+        .map(|(fork, join)| (*join, *fork))
+        .collect();
 
     for reduce in reduces {
-        let (_, _, reduct) = function.nodes[reduce.idx()].try_reduce().unwrap();
+        let (join, _, reduct) = function.nodes[reduce.idx()].try_reduce().unwrap();
+        let fork = join_fork_map[&join];
 
         // First, find all data nodes that are used by the `reduct` input of the
         // reduce, including the `reduct` itself.
@@ -249,7 +256,13 @@ pub fn reduce_cycles(
         let mut worklist = vec![reduct];
         while let Some(item) = worklist.pop() {
             for u in get_uses(&function.nodes[item.idx()]).as_ref() {
-                if !function.nodes[u.idx()].is_control() && !use_reachable.contains(u) {
+                if !function.nodes[u.idx()].is_control()
+                    && !use_reachable.contains(u)
+                    && function.nodes[u.idx()]
+                        .try_phi()
+                        .map(|(control, _)| fork_join_nest[&fork].contains(&control))
+                        .unwrap_or(true)
+                {
                     use_reachable.insert(*u);
                     worklist.push(*u);
                 }