From 8eaaa6e610d92e2b29ef1cf46a796cc27c96428d Mon Sep 17 00:00:00 2001
From: Arpad Borsos <arpad.borsos@sentry.io>
Date: Thu, 15 Feb 2024 12:00:34 +0100
Subject: [PATCH] Add ASCII fast-path for `char::is_grapheme_extended`

I discovered that `impl Debug for str` is quite slow because it ends up doing a `unicode_data::grapheme_extend::lookup` for each char, which ends up doing a binary search.

This introduces a fast-path for ASCII chars which do not have this property.

The `lookup` is thus completely gone from profiles.
---
 library/core/src/char/methods.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/library/core/src/char/methods.rs b/library/core/src/char/methods.rs
index a93b94867ce..65ae4831839 100644
--- a/library/core/src/char/methods.rs
+++ b/library/core/src/char/methods.rs
@@ -927,7 +927,7 @@ impl char {
     #[must_use]
     #[inline]
     pub(crate) fn is_grapheme_extended(self) -> bool {
-        unicode::Grapheme_Extend(self)
+        self > '\x7f' && unicode::Grapheme_Extend(self)
     }
 
     /// Returns `true` if this `char` has one of the general categories for numbers.