[libcxx-commits] [libcxx] [libc++][C++03] Cherry-pick #129348 (PR #162821)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/162821

None

>From e2a6aa1beda4316fdb63d63756e2b9691671651b Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Fri, 10 Oct 2025 12:15:10 +0200
Subject: [PATCH] [libc++][C++03] Cherry-pick #129348

---
 libcxx/include/__cxx03/regex | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libcxx/include/__cxx03/regex b/libcxx/include/__cxx03/regex
index b96d59d3a252a..f4e662d283cb9 100644
--- a/libcxx/include/__cxx03/regex
+++ b/libcxx/include/__cxx03/regex
@@ -3911,7 +3911,7 @@ _ForwardIterator basic_regex<_CharT, _Traits>::__parse_character_escape(
       ++__first;
       break;
     default:
-      if (*__first != '_' && !__traits_.isctype(*__first, ctype_base::alnum)) {
+      if (!__traits_.isctype(*__first, ctype_base::alnum)) {
         if (__str)
           *__str = *__first;
         else