Allocation space decisions are precisely made in hydrogen.

src/hydrogen-instructions.h

 // 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 5222 matching lines @@
   DECLARE_CONCRETE_INSTRUCTION(LoadGlobalGeneric)
 
  private:
   Handle<Object> name_;
   bool for_typeof_;
 };
 
 
 class HAllocate: public HTemplateInstruction<2> {
  public:
-  enum Flags {
-    CAN_ALLOCATE_IN_NEW_SPACE = 1 << 0,
-    CAN_ALLOCATE_IN_OLD_DATA_SPACE = 1 << 1,
-    CAN_ALLOCATE_IN_OLD_POINTER_SPACE = 1 << 2,
-    ALLOCATE_DOUBLE_ALIGNED = 1 << 3,
-    PREFILL_WITH_FILLER = 1 << 4
-  };
-
-  HAllocate(HValue* context, HValue* size, HType type, Flags flags)
-      : flags_(flags) {
+  HAllocate(HValue* context,
+            HValue* size,
+            HType type,
+            bool pretenure,
+            ElementsKind kind = FAST_ELEMENTS) {
     SetOperandAt(0, context);
     SetOperandAt(1, size);
     set_type(type);
     set_representation(Representation::Tagged());
     SetFlag(kTrackSideEffectDominators);
     SetGVNFlag(kChangesNewSpacePromotion);
     SetGVNFlag(kDependsOnNewSpacePromotion);
+    if (pretenure) {
+      if (IsFastDoubleElementsKind(kind)) {
+        flags_ = static_cast<HAllocate::Flags>(ALLOCATE_IN_OLD_DATA_SPACE |
+             ALLOCATE_DOUBLE_ALIGNED);
+      } else {
+        flags_ = ALLOCATE_IN_OLD_POINTER_SPACE;
+      }
+    } else {
+      flags_ = ALLOCATE_IN_NEW_SPACE;
+      if (IsFastDoubleElementsKind(kind)) {
+        flags_ = static_cast<HAllocate::Flags>(flags_ |
+            ALLOCATE_DOUBLE_ALIGNED);
+      }
+    }
   }
 
   // Maximum instance size for which allocations will be inlined.
   static const int kMaxInlineSize = 64 * kPointerSize;
 
-  static Flags DefaultFlags() {
-    return CAN_ALLOCATE_IN_NEW_SPACE;
-  }
-
-  static Flags DefaultFlags(ElementsKind kind) {
-    Flags flags = CAN_ALLOCATE_IN_NEW_SPACE;
-    if (IsFastDoubleElementsKind(kind)) {
-      flags = static_cast<HAllocate::Flags>(
-          flags | HAllocate::ALLOCATE_DOUBLE_ALIGNED);
-    }
-    return flags;
-  }
-
   HValue* context() { return OperandAt(0); }
   HValue* size() { return OperandAt(1); }
 
   virtual Representation RequiredInputRepresentation(int index) {
     if (index == 0) {
       return Representation::Tagged();
     } else {
       return Representation::Integer32();
     }
   }
 
   virtual Handle<Map> GetMonomorphicJSObjectMap() {
     return known_initial_map_;
   }
 
   void set_known_initial_map(Handle<Map> known_initial_map) {
     known_initial_map_ = known_initial_map;
   }
 
-  bool CanAllocateInNewSpace() const {
-    return (flags_ & CAN_ALLOCATE_IN_NEW_SPACE) != 0;
+  bool IsNewSpaceAllocation() const {
+    return (flags_ & ALLOCATE_IN_NEW_SPACE) != 0;
   }
 
-  bool CanAllocateInOldDataSpace() const {
-    return (flags_ & CAN_ALLOCATE_IN_OLD_DATA_SPACE) != 0;
+  bool IsOldDataSpaceAllocation() const {
+    return (flags_ & ALLOCATE_IN_OLD_DATA_SPACE) != 0;
   }
 
-  bool CanAllocateInOldPointerSpace() const {
-    return (flags_ & CAN_ALLOCATE_IN_OLD_POINTER_SPACE) != 0;
-  }
-
-  bool CanAllocateInOldSpace() const {
-    return CanAllocateInOldDataSpace() ||
-        CanAllocateInOldPointerSpace();
-  }
-
-  bool GuaranteedInNewSpace() const {
-    return CanAllocateInNewSpace() && !CanAllocateInOldSpace();
+  bool IsOldPointerSpaceAllocation() const {
+    return (flags_ & ALLOCATE_IN_OLD_POINTER_SPACE) != 0;
   }
 
   bool MustAllocateDoubleAligned() const {
     return (flags_ & ALLOCATE_DOUBLE_ALIGNED) != 0;
   }
 
   bool MustPrefillWithFiller() const {
     return (flags_ & PREFILL_WITH_FILLER) != 0;
   }
 
-  void SetFlags(Flags flags) {
-    flags_ = static_cast<HAllocate::Flags>(flags_ | flags);
+  void SetPrefillWithFiller() {

[Michael Starzinger, 2013/07/30 16:51:16]

suggestion: Maybe s/SetPrefillWithFiller/MakePrefillWithFiller/ here, but I am
also fine with leaving it as it is, up to you.

[Hannes Payer (out of office), 2013/07/31 07:02:42]

Done.

+    flags_ = static_cast<HAllocate::Flags>(flags_ | PREFILL_WITH_FILLER);
+  }
+
+  void SetDoubleAligned() {

[Michael Starzinger, 2013/07/30 16:51:16]

Likewise.

[Hannes Payer (out of office), 2013/07/31 07:02:42]

Done.

+    flags_ = static_cast<HAllocate::Flags>(flags_ | ALLOCATE_DOUBLE_ALIGNED);
   }
 
   void UpdateSize(HValue* size) {
     SetOperandAt(1, size);
   }
 
   virtual void HandleSideEffectDominator(GVNFlag side_effect,
                                          HValue* dominator);
 
   virtual void PrintDataTo(StringStream* stream);
 
   DECLARE_CONCRETE_INSTRUCTION(Allocate)
 
  private:
+  enum Flags {
+    ALLOCATE_IN_NEW_SPACE = 1 << 0,
+    ALLOCATE_IN_OLD_DATA_SPACE = 1 << 1,
+    ALLOCATE_IN_OLD_POINTER_SPACE = 1 << 2,
+    ALLOCATE_DOUBLE_ALIGNED = 1 << 3,
+    PREFILL_WITH_FILLER = 1 << 4
+  };
+
   Flags flags_;
   Handle<Map> known_initial_map_;
 };
 
 
 class HInnerAllocatedObject: public HTemplateInstruction<1> {
  public:
   HInnerAllocatedObject(HValue* value, int offset, HType type = HType::Tagged())
       : offset_(offset) {
     ASSERT(value->IsAllocate());
@@ skipping 30 matching lines @@
   if (object->IsInnerAllocatedObject()) {
     return ReceiverObjectNeedsWriteBarrier(
         HInnerAllocatedObject::cast(object)->base_object(),
         new_space_dominator);
   }
   if (object->IsConstant() && HConstant::cast(object)->IsCell()) {
     return false;
   }
   if (object != new_space_dominator) return true;
   if (object->IsAllocate()) {
-    return !HAllocate::cast(object)->GuaranteedInNewSpace();
+    return !HAllocate::cast(object)->IsNewSpaceAllocation();
   }
   return true;
 }
 
 
 class HStoreGlobalCell: public HUnaryOperation {
  public:
   HStoreGlobalCell(HValue* value,
                    Handle<PropertyCell> cell,
                    PropertyDetails details)
@@ skipping 1603 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_