From 3d8c29eaea9743ac7bd22022a878b320f4eb4396 Mon Sep 17 00:00:00 2001
From: David Smith <david_smith@apple.com>
Date: Mon, 29 Nov 2021 12:09:57 -0800
Subject: [PATCH] Early out for unequal NFC counts in String ==

---
 stdlib/public/core/StringComparison.swift | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/stdlib/public/core/StringComparison.swift b/stdlib/public/core/StringComparison.swift
index fb00567768bff..f68b17afdbb50 100644
--- a/stdlib/public/core/StringComparison.swift
+++ b/stdlib/public/core/StringComparison.swift
@@ -104,6 +104,17 @@ private func _stringCompareFastUTF8(
   bothNFC: Bool
 ) -> Bool {
   if _fastPath(bothNFC) {
+    /*
+     If we know both Strings are NFC *and* we're just checking
+     equality, then we can early-out without looking at the contents
+     if the UTF8 counts are different (without the NFC req, equal 
+     characters can have different counts). It might be nicer to do 
+     this in _binaryCompare, but we have the information about what 
+     operation we're trying to do at this level.
+     */
+    if expecting == .equal && utf8Left.count != utf8Right.count {
+        return false
+    }
     let cmp = _binaryCompare(utf8Left, utf8Right)
     return _lexicographicalCompare(cmp, 0, expecting: expecting)
   }