[c++11] Replace V8_ALIGNOF by alignof

C++ introduces the {alignof} keyword, which evaluates to an integral
constant defining the alignment of the given type. This makes
{V8_ALIGNOF} redundant.

R=ulan@chromium.org

Bug: v8:8562
Change-Id: I15a4022c2c396afba96360f218d8a04b17a9a448
Reviewed-on: https://chromium-review.googlesource.com/c/1379938
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58292}

include/v8config.h

@@ -161,12 +161,8 @@
 //
 // C++11 feature detection
 //
-//  V8_HAS_CXX11_ALIGNOF        - alignof(type) operator supported
-//
 // Compiler-specific feature detection
 //
-//  V8_HAS___ALIGNOF                    - __alignof(type) operator supported
-//  V8_HAS___ALIGNOF__                  - __alignof__(type) operator supported
 //  V8_HAS_ATTRIBUTE_ALWAYS_INLINE      - __attribute__((always_inline))
 //                                        supported
 //  V8_HAS_ATTRIBUTE_DEPRECATED         - __attribute__((deprecated)) supported
@@ -204,10 +200,6 @@
 # define V8_CC_GNU 1
 #endif
 
-// Clang defines __alignof__ as alias for __alignof
-# define V8_HAS___ALIGNOF 1
-# define V8_HAS___ALIGNOF__ V8_HAS___ALIGNOF
-
 # define V8_HAS_ATTRIBUTE_ALWAYS_INLINE (__has_attribute(always_inline))
 # define V8_HAS_ATTRIBUTE_DEPRECATED (__has_attribute(deprecated))
 # define V8_HAS_ATTRIBUTE_DEPRECATED_MESSAGE \
@@ -248,8 +240,6 @@
 # endif
 # define V8_CC_MINGW (V8_CC_MINGW32 || V8_CC_MINGW64)
 
-# define V8_HAS___ALIGNOF__ (V8_GNUC_PREREQ(4, 3, 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.
@@ -268,14 +258,10 @@
 # define V8_HAS_BUILTIN_FRAME_ADDRESS (V8_GNUC_PREREQ(2, 96, 0))
 # define V8_HAS_BUILTIN_POPCOUNT (V8_GNUC_PREREQ(3, 4, 0))
 
-# if __cplusplus >= 201103L
-#  define V8_HAS_CXX11_ALIGNOF (V8_GNUC_PREREQ(4, 8, 0))
-# endif
 #endif
 
 #if defined(_MSC_VER)
 # define V8_CC_MSVC 1
-# define V8_HAS___ALIGNOF 1
 
 # define V8_HAS_DECLSPEC_DEPRECATED 1
 # define V8_HAS_DECLSPEC_NOINLINE 1
@@ -354,25 +340,6 @@
 #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
-
 // Annotate a function indicating the caller must examine the return value.
 // Use like:
 //   int foo() V8_WARN_UNUSED_RESULT;

src/allocation.cc

@@ -122,7 +122,7 @@ void* AllocWithRetry(size_t size) {
 }
 
 void* AlignedAlloc(size_t size, size_t alignment) {
-  DCHECK_LE(V8_ALIGNOF(void*), alignment);
+  DCHECK_LE(alignof(void*), alignment);
   DCHECK(base::bits::IsPowerOfTwo(alignment));
   void* result = nullptr;
   for (int i = 0; i < kAllocationTries; ++i) {

src/profiler/cpu-profiler.cc

@@ -226,7 +226,7 @@ void SamplingEventsProcessor::Run() {
 }
 
 void* SamplingEventsProcessor::operator new(size_t size) {
-  return AlignedAlloc(size, V8_ALIGNOF(SamplingEventsProcessor));
+  return AlignedAlloc(size, alignof(SamplingEventsProcessor));
 }
 
 void SamplingEventsProcessor::operator delete(void* ptr) { AlignedFree(ptr); }