From 39dae322a4944da1e6874c088177faeb3f499c1e Mon Sep 17 00:00:00 2001
From: Makoto Kato <m_kato@ga2.so-net.ne.jp>
Date: Tue, 12 Dec 2023 00:59:27 +0000
Subject: [PATCH] Bug 1869223 - Add fast path to CountGraphemeClusters when
 text is empty. r=TYLin

When reloading https://en.wikipedia.org/wiki/Barack_Obama that is used by
browsertime benchmark, `CountGraphemeClusters` is called around 3000 times.
But half calls are that `aText` is empty.

So if we add fast path for empty text, we can avoid a lot of heap allocations
of `ICU4XGraphemeClusterBreakIteratorUtf16`.

Differential Revision: https://phabricator.services.mozilla.com/D196008
---
 intl/unicharutil/util/nsUnicodeProperties.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/intl/unicharutil/util/nsUnicodeProperties.cpp b/intl/unicharutil/util/nsUnicodeProperties.cpp
index ea7fa80ea92b..748a2d32c246 100644
--- a/intl/unicharutil/util/nsUnicodeProperties.cpp
+++ b/intl/unicharutil/util/nsUnicodeProperties.cpp
@@ -177,6 +177,10 @@ bool IsClusterExtenderExcludingJoiners(uint32_t aCh, uint8_t aCategory) {
 }
 
 uint32_t CountGraphemeClusters(Span<const char16_t> aText) {
+  if (aText.IsEmpty()) {
+    // Fast path for empty text.
+    return 0;
+  }
   intl::GraphemeClusterBreakIteratorUtf16 iter(aText);
   uint32_t result = 0;
   while (iter.Next()) {