Allocation space decisions are precisely made in hydrogen.

src/hydrogen-instructions.cc

 // Copyright 2012 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 3748 matching lines @@
           id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
     }
     return;
   }
 
   HAllocate* dominator_allocate_instr = HAllocate::cast(dominator);
   HValue* dominator_size = dominator_allocate_instr->size();
   HValue* current_size = size();
   // We can just fold allocations that are guaranteed in new space.
   // TODO(hpayer): Add support for non-constant allocation in dominator.
-  if (!GuaranteedInNewSpace() || !current_size->IsInteger32Constant() ||
-      !dominator_allocate_instr->GuaranteedInNewSpace() ||
+  if (!AllocateInNewSpace() || !current_size->IsInteger32Constant() ||
+      !dominator_allocate_instr->AllocateInNewSpace() ||
       !dominator_size->IsInteger32Constant()) {
     if (FLAG_trace_allocation_folding) {
       PrintF("#%d (%s) cannot fold into #%d (%s)\n",
           id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
     }
     return;
   }
 
   // First update the size of the dominator allocate instruction.
   int32_t dominator_size_constant =
@@ skipping 42 matching lines @@
   DeleteAndReplaceWith(dominated_allocate_instr);
   if (FLAG_trace_allocation_folding) {
     PrintF("#%d (%s) folded into #%d (%s)\n",
         id(), Mnemonic(), dominator->id(), dominator->Mnemonic());
   }
 }
 
 
 void HAllocate::PrintDataTo(StringStream* stream) {
   size()->PrintNameTo(stream);
-  if (!GuaranteedInNewSpace()) stream->Add(" (pretenure)");
+  if (!AllocateInNewSpace()) stream->Add(" (pretenure)");
 }
 
 
 HType HRegExpLiteral::CalculateInferredType() {
   return HType::JSObject();
 }
 
 
 HType HFunctionLiteral::CalculateInferredType() {
   return HType::JSObject();
@@ skipping 726 matching lines @@
       break;
     case kExternalMemory:
       stream->Add("[external-memory]");
       break;
   }
 
   stream->Add("@%d", offset());
 }
 
 } }  // namespace v8::internal