Fine-tune scheduling of parallel reductions

• Fine-tune GCM to allow nested fork-joins involving parallel reductions.

hercules_cg/src/fork_tree.rs

@@ -9,11 +9,16 @@ use crate::*;
  * c) no domination by any other fork that's also dominated by F, where we do count self-domination
  * Here too we include the non-fork start node, as key for all controls outside any fork.
  */
-pub fn fork_control_map(fork_join_nesting: &HashMap<NodeID, Vec<NodeID>>) -> HashMap<NodeID, HashSet<NodeID>> {
+pub fn fork_control_map(
+    fork_join_nesting: &HashMap<NodeID, Vec<NodeID>>,
+) -> HashMap<NodeID, HashSet<NodeID>> {
     let mut fork_control_map = HashMap::new();
     for (control, forks) in fork_join_nesting {
         let fork = forks.first().copied().unwrap_or(NodeID::new(0));
-        fork_control_map.entry(fork).or_insert_with(HashSet::new).insert(*control);
+        fork_control_map
+            .entry(fork)
+            .or_insert_with(HashSet::new)
+            .insert(*control);
     }
     fork_control_map
 }
@@ -24,13 +29,19 @@ pub fn fork_control_map(fork_join_nesting: &HashMap<NodeID, Vec<NodeID>>) -> Has
  * c) no domination by any other fork that's also dominated by F, where we don't count self-domination
  * Note that the fork_tree also includes the non-fork start node, as unique root node.
  */
-pub fn fork_tree(function: &Function, fork_join_nesting: &HashMap<NodeID, Vec<NodeID>>) -> HashMap<NodeID, HashSet<NodeID>> {
+pub fn fork_tree(
+    function: &Function,
+    fork_join_nesting: &HashMap<NodeID, Vec<NodeID>>,
+) -> HashMap<NodeID, HashSet<NodeID>> {
     let mut fork_tree = HashMap::new();
     for (control, forks) in fork_join_nesting {
         if function.nodes[control.idx()].is_fork() {
             fork_tree.entry(*control).or_insert_with(HashSet::new);
             let nesting_fork = forks.get(1).copied().unwrap_or(NodeID::new(0));
-            fork_tree.entry(nesting_fork).or_insert_with(HashSet::new).insert(*control);
+            fork_tree
+                .entry(nesting_fork)
+                .or_insert_with(HashSet::new)
+                .insert(*control);
         }
     }
     fork_tree