Literal AtomicString construction can rely on strlen optimization.

third_party/WebKit/Source/wtf/text/AtomicString.h

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  * Copyright (C) 2004, 2005, 2006, 2008 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
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  *
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  * Library General Public License for more details.
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  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
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  */
 
 #ifndef AtomicString_h
 #define AtomicString_h
 
 #include "wtf/Allocator.h"
 #include "wtf/HashTableDeletedValueType.h"
 #include "wtf/WTFExport.h"
 #include "wtf/text/CString.h"
 #include "wtf/text/WTFString.h"
+#include <cstring>
 #include <iosfwd>
 
 namespace WTF {
 
 struct AtomicStringHash;
 
 class WTF_EXPORT AtomicString {
     USING_FAST_MALLOC(AtomicString);
 public:
     static void init();
@@ skipping 13 matching lines @@
     {
     }
 
     // Constructing an AtomicString from a String / StringImpl can be expensive if
     // the StringImpl is not already atomic.
     explicit AtomicString(StringImpl* impl) : m_string(add(impl)) { }
     explicit AtomicString(const String& s) : m_string(add(s.impl())) { }
 
     AtomicString(StringImpl* baseString, unsigned start, unsigned length) : m_string(add(baseString, start, length)) { }
 
-    enum ConstructFromLiteralTag { ConstructFromLiteral };
-    AtomicString(const char* characters, unsigned length, ConstructFromLiteralTag)
-        : m_string(addFromLiteralData(characters, length))
-    {
-    }
-
-    template<unsigned charactersCount>
-    ALWAYS_INLINE AtomicString(const char (&characters)[charactersCount], ConstructFromLiteralTag)
-        : m_string(addFromLiteralData(characters, charactersCount - 1))
-    {
-        static_assert(charactersCount > 1, "AtomicString FromLiteralData should not be empty");
-        static_assert((charactersCount - 1 <= ((unsigned(~0) - sizeof(StringImpl)) / sizeof(LChar))), "AtomicString FromLiteralData cannot overflow");
-    }
-
     // Hash table deleted values, which are only constructed and never copied or destroyed.
     AtomicString(WTF::HashTableDeletedValueType) : m_string(WTF::HashTableDeletedValue) { }
     bool isHashTableDeletedValue() const { return m_string.isHashTableDeletedValue(); }
 
     static StringImpl* find(const StringImpl*);
 
     operator const String&() const { return m_string; }
     const String& getString() const { return m_string; }
 
     StringImpl* impl() const { return m_string.impl(); }
@@ skipping 68 matching lines @@
     CString latin1() const { return m_string.latin1(); }
     CString utf8(UTF8ConversionMode mode = LenientUTF8Conversion) const { return m_string.utf8(mode); }
 
 #ifndef NDEBUG
     void show() const;
 #endif
 
 private:
     String m_string;
 
-    static PassRefPtr<StringImpl> add(const LChar*);
+    ALWAYS_INLINE static PassRefPtr<StringImpl> add(const LChar* characters)

[Yuta Kitamura, 2016/03/31 06:12:06]

String literals have a type of |const char[N]|, so if you take
a string with a template, I think you don't ever need strlen
either.

I expect something like this would work:

    template <size_t n>
    void f(const char(&characters)[n]) {
        // string length == n - 1
        ...
    }

[esprehn, 2016/03/31 18:04:12]

Yeah you can do that, but that won't work for

const char* kConstant = "foo";
AtomicString string(kConstant);

but the strlen one should apply for both const char* and literal usage.

+    {
+        if (!characters)

[dcheng, 2016/03/31 05:54:36]

null is a valid input to add()?! That sounds insane.

[esprehn, 2016/03/31 18:04:12]

I'm just doing what the old code did... I agree it's crazy. We should stomp it
out.

+            return nullptr;
+        return add(characters, strlen(reinterpret_cast<const char*>(characters)));
+    }
     ALWAYS_INLINE static PassRefPtr<StringImpl> add(const char* s) { return add(reinterpret_cast<const LChar*>(s)); }
     static PassRefPtr<StringImpl> add(const LChar*, unsigned length);
     static PassRefPtr<StringImpl> add(const UChar*, unsigned length);
     ALWAYS_INLINE static PassRefPtr<StringImpl> add(const char* s, unsigned length) { return add(reinterpret_cast<const LChar*>(s), length); }
     static PassRefPtr<StringImpl> add(const UChar*, unsigned length, unsigned existingHash);
     static PassRefPtr<StringImpl> add(const UChar*);
     static PassRefPtr<StringImpl> add(StringImpl*, unsigned offset, unsigned length);
     ALWAYS_INLINE static PassRefPtr<StringImpl> add(StringImpl* r)
     {
         if (!r || r->isAtomic())
             return r;
         return addSlowCase(r);
     }
-    static PassRefPtr<StringImpl> addFromLiteralData(const char* characters, unsigned length);
     static PassRefPtr<StringImpl> addSlowCase(StringImpl*);
 #if OS(MACOSX)
     static PassRefPtr<StringImpl> add(CFStringRef);
 #endif
 
     static AtomicString fromUTF8Internal(const char*, const char*);
 };
 
 inline bool operator==(const AtomicString& a, const AtomicString& b) { return a.impl() == b.impl(); }
 WTF_EXPORT bool operator==(const AtomicString&, const LChar*);
@@ skipping 69 matching lines @@
 using WTF::AtomicString;
 using WTF::nullAtom;
 using WTF::emptyAtom;
 using WTF::starAtom;
 using WTF::xmlAtom;
 using WTF::xmlnsAtom;
 using WTF::xlinkAtom;
 
 #include "wtf/text/StringConcatenate.h"
 #endif // AtomicString_h