From de9bff27e9c5900037987b499695237ea942d6a5 Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Tue, 18 Apr 2023 00:38:16 -0400
Subject: [PATCH] Avoid unnecessary array allocation in DateTimeParse

When using DateTime{Offset}.ParseExact with a culture that employs genitive month names, the public DateTimeFormatInfo.AbbreviatedMonthGenitiveNames and DateTimeFormatInfo.MonthGenitiveNames properties are being accessed to get a string[] of the month names, but those properties clone.  If we instead access the internal non-cloning version, we save on an array allocation on each parse.
---
 .../src/System/Globalization/DateTimeFormatInfo.cs            | 2 +-
 .../src/System/Globalization/DateTimeParse.cs                 | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormatInfo.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormatInfo.cs
index 6d07fa3ff9cb10..e661479b8e4f98 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormatInfo.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeFormatInfo.cs
@@ -1204,7 +1204,7 @@ internal string InternalGetMonthName(int month, MonthNameStyles style, bool abbr
         /// Retrieve the array which contains the month names in genitive form.
         /// If this culture does not use the genitive form, the normal month name is returned.
         /// </summary>
-        private string[] InternalGetGenitiveMonthNames(bool abbreviated)
+        internal string[] InternalGetGenitiveMonthNames(bool abbreviated)
         {
             if (abbreviated)
             {
diff --git a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
index ca1594b194eb31..ddf5bae5452cbc 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Globalization/DateTimeParse.cs
@@ -3353,7 +3353,7 @@ private static bool MatchAbbreviatedMonthName(ref __DTString str, DateTimeFormat
                 // Search genitive form.
                 if ((dtfi.FormatFlags & DateTimeFormatFlags.UseGenitiveMonth) != 0)
                 {
-                    int tempResult = str.MatchLongestWords(dtfi.AbbreviatedMonthGenitiveNames, ref maxMatchStrLen);
+                    int tempResult = str.MatchLongestWords(dtfi.InternalGetGenitiveMonthNames(abbreviated: true), ref maxMatchStrLen);
 
                     // We found a longer match in the genitive month name.  Use this as the result.
                     // tempResult + 1 should be the month value.
@@ -3453,7 +3453,7 @@ private static bool MatchMonthName(ref __DTString str, DateTimeFormatInfo dtfi,
                 // Search genitive form.
                 if ((dtfi.FormatFlags & DateTimeFormatFlags.UseGenitiveMonth) != 0)
                 {
-                    int tempResult = str.MatchLongestWords(dtfi.MonthGenitiveNames, ref maxMatchStrLen);
+                    int tempResult = str.MatchLongestWords(dtfi.InternalGetGenitiveMonthNames(abbreviated: false), ref maxMatchStrLen);
                     // We found a longer match in the genitive month name.  Use this as the result.
                     // The result from MatchLongestWords is 0 ~ length of word array.
                     // So we increment the result by one to become the month value.