Very minimal SROA working

hercules_opt/src/sroa.rs

@@ -2,6 +2,7 @@ extern crate bitvec;
 extern crate hercules_ir;
 
 use std::collections::HashMap;
+use std::iter::zip;
 
 use self::bitvec::prelude::*;
 
@@ -199,7 +200,7 @@ pub fn sroa(
 
         // 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
+        let old_to_new_id_map: HashMap<NodeID, Vec<NodeID>> = to_replace
             .iter()
             .map(|old_id| match function.nodes[old_id.idx()] {
                 Node::Phi {
@@ -240,7 +241,55 @@ pub fn sroa(
             })
             .collect();
 
-        // Replace the old nodes with the new nodes.
+        // Replace the old nodes with the new nodes. Since we've already
+        // allocated the node IDs, at this point we can iterate through the to-
+        // replace nodes in an arbitrary order.
+        for (old_id, new_ids) in &old_to_new_id_map {
+            // First, add the new nodes to the node list.
+            let node = function.nodes[old_id.idx()].clone();
+            match node {
+                // Replace the original constant with constants for each field.
+                Node::Constant { id: _ } => {
+                    for (new_id, field_id) in zip(new_ids.iter(), constant_fields.iter()) {
+                        function.nodes[new_id.idx()] = Node::Constant { id: *field_id };
+                    }
+                }
+                // Replace writes using the constant as the data use with a
+                // series of writes writing the invidiual constant fields. TODO:
+                // handle the case where the constant is the collect use of the
+                // write node.
+                Node::Write {
+                    collect,
+                    data,
+                    ref indices,
+                } => {
+                    // Create the write chain.
+                    assert!(old_to_new_id_map.contains_key(&data), "PANIC: Can't handle case where write node depends on constant to SROA in the collect use yet.");
+                    let mut collect_def = collect;
+                    for (idx, (new_id, new_data_def)) in
+                        zip(new_ids.iter(), old_to_new_id_map[&data].iter()).enumerate()
+                    {
+                        let mut new_indices = indices.clone().into_vec();
+                        new_indices.push(Index::Field(idx));
+                        function.nodes[new_id.idx()] = Node::Write {
+                            collect: collect_def,
+                            data: *new_data_def,
+                            indices: new_indices.into_boxed_slice(),
+                        };
+                        collect_def = *new_id;
+                    }
+
+                    // Replace uses of the old write with the new write.
+                    for user in def_use.get_users(*old_id) {
+                        get_uses_mut(&mut function.nodes[user.idx()]).map(*old_id, collect_def);
+                    }
+                }
+                _ => todo!(),
+            }
+
+            // Delete the old node.
+            function.nodes[old_id.idx()] = Node::Start;
+        }
     }
 }