From 24079f4c1597ca7a85f1905ee068afaf58f7a0b5 Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Wed, 5 Nov 2025 13:15:35 -0800
Subject: [PATCH] deps: float v8 patch for WriteUtf8V2

Address performance regression in WriteUtf8V2

Refs: https://chromium-review.googlesource.com/c/v8/v8/+/7124103
---
 deps/v8/src/strings/unicode-inl.h | 22 +++++++++++++++++++++-
 deps/v8/src/strings/unicode.h     | 10 ++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/deps/v8/src/strings/unicode-inl.h b/deps/v8/src/strings/unicode-inl.h
index b210e18ebec6a6..3f317a32867e26 100644
--- a/deps/v8/src/strings/unicode-inl.h
+++ b/deps/v8/src/strings/unicode-inl.h
@@ -206,6 +206,17 @@ bool Utf8::IsValidCharacter(uchar c) {
           c != kBadChar);
 }
 
+template <>
+bool Utf8::IsAsciiOneByteString<uint8_t>(const uint8_t* buffer, size_t size) {
+  return simdutf::validate_ascii(reinterpret_cast<const char*>(buffer), size);
+}
+
+template <>
+bool Utf8::IsAsciiOneByteString<uint16_t>(const uint16_t* buffer, size_t size) {
+  // Necessary for template instantiation.
+  UNREACHABLE();
+}
+
 template <typename Char>
 Utf8::EncodingResult Utf8::Encode(v8::base::Vector<const Char> string,
                                   char* buffer, size_t capacity,
@@ -221,8 +232,17 @@ Utf8::EncodingResult Utf8::Encode(v8::base::Vector<const Char> string,
   const Char* characters = string.begin();
   size_t content_capacity = capacity - write_null;
   CHECK_LE(content_capacity, capacity);
-  uint16_t last = Utf16::kNoPreviousCharacter;
   size_t read_index = 0;
+  if (kSourceIsOneByte && string.size() > 0 &&
+      Utf8::IsAsciiOneByteString(characters,
+                                 std::min(string.size(), content_capacity))) {
+    size_t to_write = std::min(string.size(), content_capacity);
+    // Just memcpy when possible.
+    memcpy(buffer, characters, to_write);
+    read_index = to_write;
+    write_index = to_write;
+  }
+  uint16_t last = Utf16::kNoPreviousCharacter;
   for (; read_index < string.size(); read_index++) {
     Char character = characters[read_index];
 
diff --git a/deps/v8/src/strings/unicode.h b/deps/v8/src/strings/unicode.h
index ef1e717b1ea857..32a0b84a8399b2 100644
--- a/deps/v8/src/strings/unicode.h
+++ b/deps/v8/src/strings/unicode.h
@@ -212,6 +212,16 @@ class V8_EXPORT_PRIVATE Utf8 {
   // - valid code point range.
   static bool ValidateEncoding(const uint8_t* str, size_t length);
 
+  template <typename Char>
+  static bool IsAsciiOneByteString(const Char* buffer, size_t size);
+
+  template <>
+  inline bool IsAsciiOneByteString<uint8_t>(const uint8_t* buffer, size_t size);
+
+  template <>
+  inline bool IsAsciiOneByteString<uint16_t>(const uint16_t* buffer,
+                                             size_t size);
+
   // Encode the given characters as Utf8 into the provided output buffer.
   struct EncodingResult {
     size_t bytes_written;