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

This renames the existing V8_ALIGNAS() to V8_ALIGNED(), and introduces
V8_ALIGNAS(type, alignment) which aligns according to the type and falls
back to aligning according to alignment.

Also use __attribute__((aligned(n))) instead of __attribute__((__aligned__(n))).

R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/22999052

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16318 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

include/v8config.h

@@ -97,6 +97,7 @@
 // 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
@@ -104,7 +105,9 @@
 //
 // 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
@@ -122,7 +125,11 @@
 
 # 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))
@@ -146,7 +153,9 @@
 #  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.
@@ -164,6 +173,7 @@
 // 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))
@@ -179,6 +189,8 @@
 
 # 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)
@@ -275,16 +287,54 @@
 
 // This macro allows to specify memory alignment for structs, classes, etc.
 // Use like:
-//   class V8_ALIGNAS(16) MyClass { ... };
+//   class V8_ALIGNED(16) MyClass { ... };
-//   V8_ALIGNAS(32) int array[42];
+//   V8_ALIGNED(32) int array[42];
 #if V8_HAS_CXX11_ALIGNAS
-# define V8_ALIGNAS(n) alignas(n)
+# define V8_ALIGNED(n) alignas(n)
-#elif V8_HAS_ATTRIBUTE___ALIGNED__
+#elif V8_HAS_ATTRIBUTE_ALIGNED
-# define V8_ALIGNAS(n) __attribute__((__aligned__(n)))
+# 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_

src/circular-queue.h

@@ -70,7 +70,7 @@ class SamplingCircularQueue {
              // completely processed by the consumer.
   };
 
-  struct V8_ALIGNAS(PROCESSOR_CACHE_LINE_SIZE) Entry {
+  struct V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry {
     Entry() : marker(kEmpty) {}
     T record;
     Atomic32 marker;
@@ -79,8 +79,8 @@ class SamplingCircularQueue {
   Entry* Next(Entry* entry);
 
   Entry buffer_[Length];
-  V8_ALIGNAS(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_;
+  V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* enqueue_pos_;
-  V8_ALIGNAS(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_;
+  V8_ALIGNED(PROCESSOR_CACHE_LINE_SIZE) Entry* dequeue_pos_;
 
   DISALLOW_COPY_AND_ASSIGN(SamplingCircularQueue);
 };

src/lazy-instance.h

@@ -91,12 +91,13 @@
 #ifndef V8_LAZY_INSTANCE_H_
 #define V8_LAZY_INSTANCE_H_
 
+#include "checks.h"
 #include "once.h"
 
 namespace v8 {
 namespace internal {
 
-#define LAZY_STATIC_INSTANCE_INITIALIZER { V8_ONCE_INIT, {} }
+#define LAZY_STATIC_INSTANCE_INITIALIZER { V8_ONCE_INIT, { {} } }
 #define LAZY_DYNAMIC_INSTANCE_INITIALIZER { V8_ONCE_INIT, 0 }
 
 // Default to static mode.
@@ -111,17 +112,15 @@ struct LeakyInstanceTrait {
 
 // Traits that define how an instance is allocated and accessed.
 
-// TODO(kalmard): __alignof__ is only defined for GCC > 4.2. Fix alignment issue
-// on MIPS with other compilers.
-#if defined(__GNUC__) && (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ > 2))
-#define LAZY_ALIGN(x) __attribute__((aligned(__alignof__(x))))
-#else
-#define LAZY_ALIGN(x)
-#endif
 
 template <typename T>
 struct StaticallyAllocatedInstanceTrait {
-  typedef char StorageType[sizeof(T)] LAZY_ALIGN(T);
+  // 16-byte alignment fallback to be on the safe side here.
+  struct V8_ALIGNAS(T, 16) StorageType {
+    char x[sizeof(T)];
+  };
+
+  STATIC_ASSERT(V8_ALIGNOF(StorageType) >= V8_ALIGNOF(T));
 
   static T* MutableInstance(StorageType* storage) {
     return reinterpret_cast<T*>(storage);
@@ -133,8 +132,6 @@ struct StaticallyAllocatedInstanceTrait {
   }
 };
 
-#undef LAZY_ALIGN
-
 
 template <typename T>
 struct DynamicallyAllocatedInstanceTrait {