From 5edf9df5ef666cde604fdc3b19c35c2cb8ac0049 Mon Sep 17 00:00:00 2001
From: Chris Tate <chris@ctate.dev>
Date: Thu, 22 Oct 2026 21:19:05 -0500
Subject: [PATCH] Read only IR nodes as IR nodes in the code-unit locals pass

---
 packages/compiler/src/ir/char-unit-locals.ts | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/packages/compiler/src/ir/char-unit-locals.ts b/packages/compiler/src/ir/char-unit-locals.ts
index 4008f4e1e..beeeffaf3 100644
--- a/packages/compiler/src/ir/char-unit-locals.ts
+++ b/packages/compiler/src/ir/char-unit-locals.ts
@@ -161,6 +161,10 @@ function unitLocal(local: IrLocal): IrLocal {
  * declaration from a one-argument charAt, a one-unit test, or a switch
  * over one-unit cases. */
 function understoodMention(node: Record<string, unknown>): string | null {
+  // count() visits every object in the body (types, locations, cases), so
+  // only the node kinds handled here are read as IR nodes
+  const kind = node.kind;
+  if (kind !== "varDecl" && kind !== "strEq" && kind !== "strCmp" && kind !== "switch") return null;
   const n = node as unknown as IrExpr | IrStmt;
   if (n.kind === "varDecl") return n.init && isCharAt(n.init) ? n.localId : null;
   if (n.kind === "strEq" || n.kind === "strCmp") return unitUse(n)?.id ?? null;