Add V8_ALIGNAS() and V8_ALIGNOF() and use that in lazy-instance.h.

include/v8config.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 79 matching lines @@
 // Compiler detection
 //
 //  V8_CC_CLANG   - Clang
 //  V8_CC_GNU     - GNU C++
 //  V8_CC_MINGW   - Minimalist GNU for Windows
 //  V8_CC_MSVC    - Microsoft Visual C/C++
 //
 // C++11 feature detection
 //
 //  V8_HAS_CXX11_ALIGNAS        - alignas specifier supported
+//  V8_HAS_CXX11_ALIGNOF        - alignof(type) operator supported
 //  V8_HAS_CXX11_STATIC_ASSERT  - static_assert() supported
 //  V8_HAS_CXX11_DELETE         - deleted functions supported
 //  V8_HAS_CXX11_FINAL          - final marker supported
 //  V8_HAS_CXX11_OVERRIDE       - override marker supported
 //
 // Compiler-specific feature detection
 //
-//  V8_HAS_ATTRIBUTE___ALIGNED__    - __attribute__((__aligned__(n))) supported
+//  V8_HAS___ALIGNOF                - __alignof(type) operator supported
+//  V8_HAS___ALIGNOF__              - __alignof__(type) operator supported
+//  V8_HAS_ATTRIBUTE_ALIGNED        - __attribute__((aligned(n))) supported
 //  V8_HAS_ATTRIBUTE_ALWAYS_INLINE  - __attribute__((always_inline)) supported
 //  V8_HAS_ATTRIBUTE_DEPRECATED     - __attribute__((deprecated)) supported
 //  V8_HAS_ATTRIBUTE_VISIBILITY     - __attribute__((visibility)) supported
 //  V8_HAS_BUILTIN_EXPECT           - __builtin_expect() supported
 //  V8_HAS_DECLSPEC_ALIGN           - __declspec(align(n)) supported
 //  V8_HAS_DECLSPEC_DEPRECATED      - __declspec(deprecated) supported
 //  V8_HAS___FINAL                  - __final supported in non-C++11 mode
 //  V8_HAS___FORCEINLINE            - __forceinline supported
 //  V8_HAS_SEALED                   - MSVC style sealed marker supported
 
 #if defined(__clang__)
 
 // Don't treat clang as GCC.
 # define V8_GNUC_PREREQ(major, minor, patchlevel) 0
 
 # define V8_CC_CLANG 1
 
-# define V8_HAS_ATTRIBUTE___ALIGNED__ (__has_attribute(__aligned__))
+// Clang defines __alignof__ as alias for __alignof
+# define V8_HAS___ALIGNOF 1
+# define V8_HAS___ALIGNOF__ V8_HAS___ALIGNOF
+
+# define V8_HAS_ATTRIBUTE_ALIGNED (__has_attribute(aligned))
 # define V8_HAS_ATTRIBUTE_ALWAYS_INLINE (__has_attribute(always_inline))
 # define V8_HAS_ATTRIBUTE_DEPRECATED (__has_attribute(deprecated))
 # define V8_HAS_ATTRIBUTE_VISIBILITY (__has_attribute(visibility))
 
 # define V8_HAS_BUILTIN_EXPECT (__has_builtin(__builtin_expect))
 
 # define V8_HAS_CXX11_ALIGNAS (__has_feature(cxx_alignas))
 # define V8_HAS_CXX11_STATIC_ASSERT (__has_feature(cxx_static_assert))
 # define V8_HAS_CXX11_DELETE (__has_feature(cxx_deleted_functions))
 # define V8_HAS_CXX11_FINAL (__has_feature(cxx_override_control))
 # define V8_HAS_CXX11_OVERRIDE (__has_feature(cxx_override_control))
 
 #elif defined(__GNUC__)
 
 # define V8_GNUC_PREREQ(major, minor, patchlevel)                         \
     ((__GNUC__ * 10000 + __GNUC_MINOR__ * 100 + __GNUC_PATCHLEVEL__) >=   \
      ((major) * 10000 + (minor) * 100 + (patchlevel)))
 
 # define V8_CC_GNU 1
 # if defined(__MINGW32__)
 #  define V8_CC_MINGW 1
 # endif
 
-# define V8_HAS_ATTRIBUTE___ALIGNED__ (V8_GNUC_PREREQ(2, 95, 0))
+# define V8_HAS___ALIGNOF__ (V8_GNUC_PREREQ(4, 3, 0))
+
+# define V8_HAS_ATTRIBUTE_ALIGNED (V8_GNUC_PREREQ(2, 95, 0))
 // always_inline is available in gcc 4.0 but not very reliable until 4.4.
 // Works around "sorry, unimplemented: inlining failed" build errors with
 // older compilers.
 # define V8_HAS_ATTRIBUTE_ALWAYS_INLINE (V8_GNUC_PREREQ(4, 4, 0))
 # define V8_HAS_ATTRIBUTE_DEPRECATED (V8_GNUC_PREREQ(3, 4, 0))
 # define V8_HAS_ATTRIBUTE_VISIBILITY (V8_GNUC_PREREQ(4, 3, 0))
 
 # define V8_HAS_BUILTIN_EXPECT (V8_GNUC_PREREQ(2, 96, 0))
 
 // g++ requires -std=c++0x or -std=gnu++0x to support C++11 functionality
 // without warnings (functionality used by the macros below).  These modes
 // are detectable by checking whether __GXX_EXPERIMENTAL_CXX0X__ is defined or,
 // more standardly, by checking whether __cplusplus has a C++11 or greater
 // value. Current versions of g++ do not correctly set __cplusplus, so we check
 // both for forward compatibility.
 # if defined(__GXX_EXPERIMENTAL_CXX0X__) || __cplusplus >= 201103L
 #  define V8_HAS_CXX11_ALIGNAS (V8_GNUC_PREREQ(4, 8, 0))
+#  define V8_HAS_CXX11_ALIGNOF (V8_GNUC_PREREQ(4, 8, 0))
 #  define V8_HAS_CXX11_STATIC_ASSERT (V8_GNUC_PREREQ(4, 3, 0))
 #  define V8_HAS_CXX11_DELETE (V8_GNUC_PREREQ(4, 4, 0))
 #  define V8_HAS_CXX11_OVERRIDE (V8_GNUC_PREREQ(4, 7, 0))
 #  define V8_HAS_CXX11_FINAL (V8_GNUC_PREREQ(4, 7, 0))
 # else
 // '__final' is a non-C++11 GCC synonym for 'final', per GCC r176655.
 #  define V8_HAS___FINAL (V8_GNUC_PREREQ(4, 7, 0))
 # endif
 
 #elif defined(_MSC_VER)
 
 # define V8_GNUC_PREREQ(major, minor, patchlevel) 0
 
 # define V8_CC_MSVC 1
 
+# define V8_HAS___ALIGNOF 1
+
 // Override control was added with Visual Studio 2005, but
 // Visual Studio 2010 and earlier spell "final" as "sealed".
 # define V8_HAS_CXX11_FINAL (_MSC_VER >= 1700)
 # define V8_HAS_CXX11_OVERRIDE (_MSC_VER >= 1400)
 # define V8_HAS_SEALED (_MSC_VER >= 1400)
 
 # define V8_HAS_DECLSPEC_ALIGN 1
 # define V8_HAS_DECLSPEC_DEPRECATED (_MSC_VER >= 1300)
 
 # define V8_HAS___FORCEINLINE 1
@@ skipping 76 matching lines @@
 # define V8_FINAL __final
 #elif V8_HAS_SEALED
 # define V8_FINAL sealed
 #else
 # define V8_FINAL /* NOT SUPPORTED */
 #endif
 
 
 // This macro allows to specify memory alignment for structs, classes, etc.
 // Use like:
-//   class V8_ALIGNAS(16) MyClass { ... };
-//   V8_ALIGNAS(32) int array[42];
+//   class V8_ALIGNED(16) MyClass { ... };
+//   V8_ALIGNED(32) int array[42];
 #if V8_HAS_CXX11_ALIGNAS
-# define V8_ALIGNAS(n) alignas(n)
-#elif V8_HAS_ATTRIBUTE___ALIGNED__
-# define V8_ALIGNAS(n) __attribute__((__aligned__(n)))
+# define V8_ALIGNED(n) alignas(n)
+#elif V8_HAS_ATTRIBUTE_ALIGNED
+# define V8_ALIGNED(n) __attribute__((aligned(n)))
 #elif V8_HAS_DECLSPEC_ALIGN
-# define V8_ALIGNAS(n) __declspec(align(n))
+# define V8_ALIGNED(n) __declspec(align(n))
 #else
-# define V8_ALIGNAS(n) /* NOT SUPPORTED */
+# define V8_ALIGNED(n) /* NOT SUPPORTED */
+#endif
+
+
+// This macro is similar to V8_ALIGNED(), but takes a type instead of size
+// in bytes. If the compiler does not supports using the alignment of the
+// |type|, it will align according to the |alignment| instead. For example,
+// Visual Studio C++ cannot combine __declspec(align) and __alignof. The
+// |alignment| must be a literal that is used as a kind of worst-case fallback
+// alignment.
+// Use like:
+//   struct V8_ALIGNAS(AnotherClass, 16) NewClass { ... };
+//   V8_ALIGNAS(double, 8) int array[100];
+#if V8_HAS_CXX11_ALIGNAS
+# define V8_ALIGNAS(type, alignment) alignas(type)
+#elif V8_HAS___ALIGNOF__ && V8_HAS_ATTRIBUTE_ALIGNED
+# define V8_ALIGNAS(type, alignment) __attribute__((aligned(__alignof__(type))))
+#else
+# define V8_ALIGNAS(type, alignment) V8_ALIGNED(alignment)
+#endif
+
+
+// This macro returns alignment in bytes (an integer power of two) required for
+// any instance of the given type, which is either complete type, an array type,
+// or a reference type.
+// Use like:
+//   size_t alignment = V8_ALIGNOF(double);
+#if V8_HAS_CXX11_ALIGNOF
+# define V8_ALIGNOF(type) alignof(type)
+#elif V8_HAS___ALIGNOF
+# define V8_ALIGNOF(type) __alignof(type)
+#elif V8_HAS___ALIGNOF__
+# define V8_ALIGNOF(type) __alignof__(type)
+#else
+// Note that alignment of a type within a struct can be less than the
+// alignment of the type stand-alone (because of ancient ABIs), so this
+// should only be used as a last resort.
+namespace v8 { template <typename T> class AlignOfHelper { char c; T t; }; }
+# define V8_ALIGNOF(type) (sizeof(::v8::AlignOfHelper<type>) - sizeof(type))
 #endif
 
 #endif  // V8CONFIG_H_