8-byte align C stack on Linux and Windows.

src/platform-linux.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 194 matching lines @@
   return strndup(str, n);
 }
 
 
 double OS::nan_value() {
   return NAN;
 }
 
 
 int OS::ActivationFrameAlignment() {
-  // No constraint on Linux.
-  return 0;
+  // Floating point code runs faster if the stack is 8-byte aligned.
+  return 8;
 }
 
 
 // We keep the lowest and highest addresses mapped as a quick way of
 // determining that pointers are outside the heap (used mostly in assertions
 // and verification).  The estimate is conservative, ie, not all addresses in
 // 'allocated' space are actually allocated to our heap.  The range is
 // [lowest, highest), inclusive on the low and and exclusive on the high end.
 static void* lowest_ever_allocated = reinterpret_cast<void*>(-1);
 static void* highest_ever_allocated = reinterpret_cast<void*>(0);
@@ skipping 627 matching lines @@
   }
 
   // This sampler is no longer the active sampler.
   active_sampler_ = NULL;
   active_ = false;
 }
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal