Allocation space decisions are precisely made in hydrogen.

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index 651ce0a0e8902767550da76a0bd97de5e3c8000f..4e821ac95acb70d2f4c2e3324edf2a0dd1d351a7 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -434,10 +434,9 @@ HValue* CodeStubGraphBuilder<FastCloneShallowObjectStub>::BuildCodeStub() {
   checker.Then();
 
   HValue* size_in_bytes = AddInstruction(new(zone) HConstant(size));
-  HAllocate::Flags flags = HAllocate::CAN_ALLOCATE_IN_NEW_SPACE;
+  HAllocate::Flags flags = HAllocate::DefaultFlags();
   if (isolate()->heap()->ShouldGloballyPretenure()) {
-    flags = static_cast<HAllocate::Flags>(
-       flags | HAllocate::CAN_ALLOCATE_IN_OLD_POINTER_SPACE);
+    flags = HAllocate::ALLOCATE_IN_OLD_POINTER_SPACE;
   }
 
   HInstruction* object = AddInstruction(new(zone)
@@ -466,9 +465,7 @@ HValue* CodeStubGraphBuilder<CreateAllocationSiteStub>::BuildCodeStub() {
   Zone* zone = this->zone();
 
   HValue* size = AddInstruction(new(zone) HConstant(AllocationSite::kSize));
-  HAllocate::Flags flags = HAllocate::DefaultFlags();
-  flags = static_cast<HAllocate::Flags>(
-      flags | HAllocate::CAN_ALLOCATE_IN_OLD_POINTER_SPACE);
+  HAllocate::Flags flags = HAllocate::ALLOCATE_IN_OLD_POINTER_SPACE;
   HInstruction* object = AddInstruction(new(zone)
       HAllocate(context(), size, HType::JSObject(), flags));