8-byte align C stack on Linux and Windows.

src/platform-win32.cc

 // Copyright 2006-2008 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 1280 matching lines @@
 #ifdef _MSC_VER
   static const __int64 nanval = 0xfff8000000000000;
   return *reinterpret_cast<const double*>(&nanval);
 #else  // _MSC_VER
   return NAN;
 #endif  // _MSC_VER
 }
 
 
 int OS::ActivationFrameAlignment() {
-  // No constraint on Windows.
-  return 0;
+  // Floating point code runs faster if the stack is 8-byte aligned.
+  return 8;
 }
 
 
 bool VirtualMemory::IsReserved() {
   return address_ != NULL;
 }
 
 
 VirtualMemory::VirtualMemory(size_t size) {
   address_ = VirtualAlloc(NULL, size, MEM_RESERVE, PAGE_NOACCESS);
@@ skipping 510 matching lines @@
 
   // Release the thread handles
   CloseHandle(data_->sampler_thread_);
   CloseHandle(data_->profiled_thread_);
 }
 
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal