From 9e2fc16c32e710ff342d1932ef4668bbcfb22d86 Mon Sep 17 00:00:00 2001
From: Yuya Tanaka <yuya.presto@gmail.com>
Date: Wed, 13 Oct 2021 08:07:21 +0900
Subject: [PATCH] Improve perf of unions with many primitives (#45220)

---
 src/compiler/checker.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 3d54f2e9db5..c11ce26d883 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -22652,8 +22652,9 @@ namespace ts {
         // constituent types keyed by the literal types of the property by that name in each constituent type.
         function getKeyPropertyName(unionType: UnionType): __String | undefined {
             const types = unionType.types;
-            // We only construct maps for large unions with non-primitive constituents.
-            if (types.length < 10 || getObjectFlags(unionType) & ObjectFlags.PrimitiveUnion) {
+            // We only construct maps for unions with many non-primitive constituents.
+            if (types.length < 10 || getObjectFlags(unionType) & ObjectFlags.PrimitiveUnion ||
+                countWhere(types, t => !!(t.flags & (TypeFlags.Object | TypeFlags.InstantiableNonPrimitive))) < 10) {
                 return undefined;
             }
             if (unionType.keyPropertyName === undefined) {