Refactor: Use root_purity instead of global_purity

This commit refactors the purity analysis from using a
`HashMap<GlobalIdx, Purity>` to a `Vec<Purity>` indexed by
`GlobalIdx.0`.

This change simplifies the data structure and makes purity lookups more
efficient. The `Binder`'s `globals` field has also been removed as it
was not being used.

src/ast/compiler/optimizer/engine.rs

@@ -1,11 +1,10 @@
 use crate::ast::compiler::bound_nodes::{
-    Address, AnalyzedNode, BoundKind, GlobalAnalyzedRegistry, GlobalIdx, UpvalueIdx,
+    Address, AnalyzedNode, BoundKind, GlobalAnalyzedRegistry, UpvalueIdx,
 };
 use crate::ast::nodes::Node;
 use crate::ast::types::{Purity, Value};
 use crate::ast::vm::Closure;
 use std::cell::RefCell;
-use std::collections::HashMap;
 use std::rc::Rc;
 
 use super::folder::Folder;
@@ -17,7 +16,7 @@ pub struct Optimizer {
     pub enabled: bool,
     max_passes: usize,
     pub globals: Option<Rc<RefCell<Vec<Value>>>>,
-    pub global_purity: Option<Rc<RefCell<HashMap<GlobalIdx, Purity>>>>,
+    pub root_purity: Option<Rc<RefCell<Vec<Purity>>>>,
     pub lambda_registry: Option<Rc<RefCell<GlobalAnalyzedRegistry>>>,
 }
 
@@ -27,7 +26,7 @@ impl Optimizer {
             enabled,
             max_passes: 5,
             globals: None,
-            global_purity: None,
+            root_purity: None,
             lambda_registry: None,
         }
     }
@@ -37,8 +36,8 @@ impl Optimizer {
         self
     }
 
-    pub fn with_purity(mut self, purity: Rc<RefCell<HashMap<GlobalIdx, Purity>>>) -> Self {
-        self.global_purity = Some(purity);
+    pub fn with_purity(mut self, purity: Rc<RefCell<Vec<Purity>>>) -> Self {
+        self.root_purity = Some(purity);
         self
     }
 
@@ -79,7 +78,7 @@ impl Optimizer {
         path: &mut PathTracker,
         base_sub: Option<SubstitutionMap>,
     ) -> Option<Rc<AnalyzedNode>> {
-        let inliner = Inliner::new(&self.globals, &self.global_purity);
+        let inliner = Inliner::new(&self.globals, &self.root_purity);
         let mut inner_sub = base_sub.unwrap_or_else(|| sub.new_for_inlining());
         
         if inliner.prepare_beta_reduction(params, arg_nodes, body, &mut inner_sub).is_some() {
@@ -105,7 +104,7 @@ impl Optimizer {
     ) -> Rc<AnalyzedNode> {
         let node = &*node_rc;
         let folder = Folder::new(&self.globals);
-        let inliner = Inliner::new(&self.globals, &self.global_purity);
+        let inliner = Inliner::new(&self.globals, &self.root_purity);
         
         let (new_kind, metrics) = match &node.kind {
             BoundKind::Get { addr, name } => {
@@ -215,11 +214,13 @@ impl Optimizer {
 
                 if let Address::Global(global_index) = addr
                     && value_opt.ty.purity > Purity::Impure
-                    && let Some(purity_rc) = &self.global_purity
+                    && let Some(purity_rc) = &self.root_purity
                 {
-                    purity_rc
-                        .borrow_mut()
-                        .insert(*global_index, value_opt.ty.purity);
+                    let mut pr = purity_rc.borrow_mut();
+                    let idx = global_index.0 as usize;
+                    if idx < pr.len() {
+                        pr[idx] = value_opt.ty.purity;
+                    }
                 }
 
                 if Rc::ptr_eq(&value_opt, value) {