Misc.

• Add region nodes after fork-joins to get better block placements.

hercules_opt/src/gcm.rs

@@ -221,6 +221,31 @@ fn preliminary_fixups(
         }
     }
 
+    // Add region nodes between join nodes and loop headers to aid in block
+    // placement.
+    for (_, join) in fork_join_map {
+        let control_user = editor
+            .get_users(*join)
+            .filter(|id| nodes[id.idx()].is_control())
+            .next()
+            .unwrap();
+        if nodes[control_user.idx()].is_fork()
+            || nodes[control_user.idx()]
+                .try_region()
+                .map(|preds| preds.len() > 1)
+                .unwrap_or(false)
+        {
+            let success = editor.edit(|mut edit| {
+                let region = edit.add_node(Node::Region {
+                    preds: Box::new([*join]),
+                });
+                edit.replace_all_uses_where(*join, region, |id| *id == control_user)
+            });
+            assert!(success);
+            return true;
+        }
+    }
+
     false
 }