assemble old to new id mapping

hercules_opt/src/sroa.rs

 extern crate bitvec;
 extern crate hercules_ir;
 
+use std::collections::HashMap;
+
 use self::bitvec::prelude::*;
 
 use self::hercules_ir::dataflow::*;
@@ -195,8 +197,48 @@ pub fn sroa(
         let to_replace = sroa_dfs(constant_node_id, function, def_use);
         println!("{:?}", to_replace);
 
-        // Assemble a mapping from old nodes acting on the product constant to
-        // new nodes operating on the field constants.
+        // Assemble a mapping from old nodes IDs acting on the product constant
+        // to new nodes IDs operating on the field constants.
+        let map: HashMap<NodeID, Vec<NodeID>> = to_replace
+            .iter()
+            .map(|old_id| match function.nodes[old_id.idx()] {
+                Node::Phi {
+                    control: _,
+                    data: _,
+                }
+                | Node::Reduce {
+                    control: _,
+                    init: _,
+                    reduct: _,
+                }
+                | Node::Constant { id: _ }
+                | Node::Ternary {
+                    op: _,
+                    first: _,
+                    second: _,
+                    third: _,
+                }
+                | Node::Write {
+                    collect: _,
+                    data: _,
+                    indices: _,
+                } => {
+                    let new_ids = (0..constant_fields.len())
+                        .map(|_| {
+                            let id = NodeID::new(function.nodes.len());
+                            function.nodes.push(Node::Start);
+                            id
+                        })
+                        .collect();
+                    (*old_id, new_ids)
+                }
+                Node::Read {
+                    collect: _,
+                    indices: _,
+                } => (*old_id, vec![]),
+                _ => panic!("PANIC: Invalid node using a constant product found during SROA."),
+            })
+            .collect();
 
         // Replace the old nodes with the new nodes.
     }