[KURL] Avoid re-hashing input if is already canonicalized

third_party/WebKit/Source/platform/weborigin/KURL.cpp

 /*
  * Copyright (C) 2004, 2007, 2008, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2012 Research In Motion Limited. All rights reserved.
  * Copyright (C) 2008, 2009, 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 700 matching lines @@
     return url::FindAndCompareScheme(asURLChar8Subtle(url), url.length(),
                                      protocol, 0);
   return url::FindAndCompareScheme(url.characters16(), url.length(), protocol,
                                    0);
 }
 
 void KURL::init(const KURL& base,
                 const String& relative,
                 const WTF::TextEncoding* queryEncoding) {
   if (!relative.isNull() && relative.is8Bit()) {
-    StringUTF8Adaptor relativeUTF8(relative);
-    init(base, relativeUTF8.data(), relativeUTF8.length(), queryEncoding);
-  } else
-    init(base, relative.characters16(), relative.length(), queryEncoding);

[esprehn, 2016/10/25 22:23:50]

We go down this path when relative.isNull() which is strange.

[Charlie Harrison, 2016/10/27 02:12:36]

The null check is just for the is8Bit check which reaches into m_impl. Other
than that the code is robust to nulls.

+    // Avoid using StringUTF8Adaptor because we want the possibly non-ascii data
+    // exposed to init<CHAR> as a String to avoid re-allocation.
+    String utf8 = relative.containsOnlyASCII()
+                      ? relative
+                      : String::fromUTF8(relative.utf8());
+    init(base, reinterpret_cast<const char*>(utf8.characters8()), utf8.length(),
+         queryEncoding, utf8);
+  } else {
+    init(base, relative.characters16(), relative.length(), queryEncoding,
+         relative);
+  }
   initProtocolIsInHTTPFamily();
   initInnerURL();
 }
 
 template <typename CHAR>
 void KURL::init(const KURL& base,
                 const CHAR* relative,
                 int relativeLength,
-                const WTF::TextEncoding* queryEncoding) {
+                const WTF::TextEncoding* queryEncoding,
+                const String& originalRelative) {
   // As a performance optimization, we do not use the charset converter
   // if encoding is UTF-8 or other Unicode encodings. Note that this is
   // per HTML5 2.5.3 (resolving URL). The URL canonicalizer will be more
   // efficient with no charset converter object because it can do UTF-8
   // internally with no extra copies.
 
   // We feel free to make the charset converter object every time since it's
   // just a wrapper around a reference.
   KURLCharsetConverter charsetConverterObject(queryEncoding);
   KURLCharsetConverter* charsetConverter =
       (!queryEncoding || isUnicodeEncoding(queryEncoding))
           ? 0
           : &charsetConverterObject;
 
   StringUTF8Adaptor baseUTF8(base.getString());
 
   url::RawCanonOutputT<char> output;
   m_isValid = url::ResolveRelative(baseUTF8.data(), baseUTF8.length(),
                                    base.m_parsed, relative, relativeLength,
                                    charsetConverter, &output, &m_parsed);
 
-  // See FIXME in KURLPrivate in the header. If canonicalization has not
-  // changed the string, we can avoid an extra allocation by using assignment.
-  m_string = AtomicString::fromUTF8(output.data(), output.length());
+  // If the canonicalization has not changed the string, avoid re-allocating.
+  // Note: because we are canonicalizing into narrow characters, this check will
+  // always be false for 16 bit inputs.
+  if (output.length() == relativeLength &&
+      !memcmp(output.data(), relative, relativeLength)) {
+    m_string = AtomicString(originalRelative);
+  } else {
+    m_string = AtomicString::fromUTF8(output.data(), output.length());
+  }
 }
 
 void KURL::initInnerURL() {
   if (!m_isValid) {
     m_innerURL.reset();
     return;
   }
   if (url::Parsed* innerParsed = m_parsed.inner_parsed())
     m_innerURL = wrapUnique(new KURL(
         ParsedURLString,
@@ skipping 100 matching lines @@
   m_parsed = newParsed;
   m_string = AtomicString::fromUTF8(output.data(), output.length());
 }
 
 bool KURL::isSafeToSendToAnotherThread() const {
   return m_string.isSafeToSendToAnotherThread() &&
          (!m_innerURL || m_innerURL->isSafeToSendToAnotherThread());
 }
 
 }  // namespace blink