Allocate the right number of fast context slots on X64. Ported from ia32....

src/arm/codegen-arm.cc

 // Copyright 2010 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 173 matching lines @@
 
     if (info->mode() == CompilationInfo::PRIMARY) {
       frame_->Enter();
       // tos: code slot
 
       // Allocate space for locals and initialize them.  This also checks
       // for stack overflow.
       frame_->AllocateStackSlots();
 
       VirtualFrame::SpilledScope spilled_scope(frame_);
-      int heap_slots = scope()->num_heap_slots();
+      int heap_slots = scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
       if (heap_slots > 0) {
         // Allocate local context.
         // Get outer context and create a new context based on it.
         __ ldr(r0, frame_->Function());
         frame_->EmitPush(r0);
         if (heap_slots <= FastNewContextStub::kMaximumSlots) {
           FastNewContextStub stub(heap_slots);
           frame_->CallStub(&stub, 1);
         } else {
           frame_->CallRuntime(Runtime::kNewContext, 1);
@@ skipping 9696 matching lines @@
 
   // Just jump to runtime to add the two strings.
   __ bind(&string_add_runtime);
   __ TailCallRuntime(Runtime::kStringAdd, 2, 1);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal