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/inliner.rs

@@ -1,8 +1,8 @@
-use crate::ast::compiler::bound_nodes::{Address, AnalyzedNode, BoundKind, GlobalIdx, LocalSlot};
+use crate::ast::compiler::bound_nodes::{Address, AnalyzedNode, BoundKind, LocalSlot};
 use crate::ast::types::{Purity, Value};
 use crate::ast::vm::Closure;
 use std::cell::RefCell;
-use std::collections::{HashMap, HashSet};
+use std::collections::HashSet;
 use std::rc::Rc;
 
 use super::substitution_map::SubstitutionMap;
@@ -10,17 +10,17 @@ use super::utils::UsageInfo;
 
 pub struct Inliner<'a> {
     pub globals: &'a Option<Rc<RefCell<Vec<Value>>>>,
-    pub global_purity: &'a Option<Rc<RefCell<HashMap<GlobalIdx, Purity>>>>,
+    pub root_purity: &'a Option<Rc<RefCell<Vec<Purity>>>>,
 }
 
 impl<'a> Inliner<'a> {
     pub fn new(
         globals: &'a Option<Rc<RefCell<Vec<Value>>>>,
-        global_purity: &'a Option<Rc<RefCell<HashMap<GlobalIdx, Purity>>>>,
+        root_purity: &'a Option<Rc<RefCell<Vec<Purity>>>>,
     ) -> Self {
         Self {
             globals,
-            global_purity,
+            root_purity,
         }
     }
 
@@ -48,10 +48,10 @@ impl<'a> Inliner<'a> {
         }
 
         if let Address::Global(idx) = addr {
-            if let Some(purity_rc) = &self.global_purity {
+            if let Some(purity_rc) = &self.root_purity {
                 let purity = purity_rc
                     .borrow()
-                    .get(&idx)
+                    .get(idx.0 as usize)
                     .cloned()
                     .unwrap_or(Purity::Impure);
                 return purity >= Purity::Pure;