Optimize utf8length for utf16 values

anonrig · V8 LUCI CQ · commit b25cd62c7ba2 · 2025-11-17T07:11:56.000-08:00
Change-Id: I4d9546ab45264852f52361123e86fa3b38d79e45 Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/7142019 Reviewed-by: Anton Bikineev <bikineev@chromium.org> Reviewed-by: Erik Corry <erikcorry@chromium.org> Commit-Queue: Erik Corry <erikcorry@chromium.org> Cr-Commit-Position: refs/heads/main@{#103754}
diff --git a/src/objects/string-inl.h b/src/objects/string-inl.h
@@ -1221,6 +1221,12 @@ size_t String::Utf8Length(Isolate* isolate, DirectHandle<String> string) {
         reinterpret_cast<const char*>(vec.begin()), vec.size());
   }
 
+  base::Vector<const base::uc16> vec = content.ToUC16Vector();
+  const char16_t* data = reinterpret_cast<const char16_t*>(vec.begin());
+  if (simdutf::validate_utf16(data, vec.size())) {
+    return simdutf::utf8_length_from_utf16(data, vec.size());
+  }
+
   // TODO(419496232): Use simdutf once upstream bug is resolved.
   size_t utf8_length = 0;
   uint16_t last_character = unibrow::Utf16::kNoPreviousCharacter;
