[crankshaft] Fragmentation-free allocation folding.

src/crankshaft/hydrogen-instructions.h

Index: src/crankshaft/hydrogen-instructions.h
diff --git a/src/crankshaft/hydrogen-instructions.h b/src/crankshaft/hydrogen-instructions.h
index a98efe651b733c63e56dae14dd1328eb7fd37418..49e429fe7cb46a5bbc436f24fe1e2b5eb7b5c888 100644
--- a/src/crankshaft/hydrogen-instructions.h
+++ b/src/crankshaft/hydrogen-instructions.h
@@ -4939,8 +4939,7 @@ class HLoadGlobalGeneric final : public HTemplateInstruction<2> {
   FeedbackVectorSlot slot_;
 };
 
-
-class HAllocate final : public HTemplateInstruction<2> {
+class HAllocate final : public HTemplateInstruction<3> {
  public:
   static bool CompatibleInstanceTypes(InstanceType type1,
                                       InstanceType type2) {
@@ -4951,9 +4950,10 @@ class HAllocate final : public HTemplateInstruction<2> {
   static HAllocate* New(
       Isolate* isolate, Zone* zone, HValue* context, HValue* size, HType type,
       PretenureFlag pretenure_flag, InstanceType instance_type,
+      HValue* dominator,
       Handle<AllocationSite> allocation_site = Handle<AllocationSite>::null()) {
-    return new(zone) HAllocate(context, size, type, pretenure_flag,
-        instance_type, allocation_site);
+    return new (zone) HAllocate(context, size, type, pretenure_flag,
+                                instance_type, dominator, allocation_site);
   }
 
   // Maximum instance size for which allocations will be inlined.
@@ -4961,13 +4961,7 @@ class HAllocate final : public HTemplateInstruction<2> {
 
   HValue* context() const { return OperandAt(0); }
   HValue* size() const { return OperandAt(1); }
-
-  bool has_size_upper_bound() { return size_upper_bound_ != NULL; }
-  HConstant* size_upper_bound() { return size_upper_bound_; }
-  void set_size_upper_bound(HConstant* value) {
-    DCHECK(size_upper_bound_ == NULL);
-    size_upper_bound_ = value;
-  }
+  HValue* allocation_folding_dominator() const { return OperandAt(2); }
 
   Representation RequiredInputRepresentation(int index) override {
     if (index == 0) {
@@ -5005,14 +4999,27 @@ class HAllocate final : public HTemplateInstruction<2> {
     flags_ = static_cast<HAllocate::Flags>(flags_ | PREFILL_WITH_FILLER);
   }
 
-  bool MustClearNextMapWord() const {
-    return (flags_ & CLEAR_NEXT_MAP_WORD) != 0;
-  }
-
   void MakeDoubleAligned() {
     flags_ = static_cast<HAllocate::Flags>(flags_ | ALLOCATE_DOUBLE_ALIGNED);
   }
 
+  void MakeAllocationFoldingDominator() {
+    flags_ =
+        static_cast<HAllocate::Flags>(flags_ | ALLOCATION_FOLDING_DOMINATOR);
+  }
+
+  bool IsAllocationFoldingDominator() {
+    return (flags_ & ALLOCATION_FOLDING_DOMINATOR) != 0;
+  }
+
+  void MakeFoldedAllocation() {

[Michael Lippautz, 2016/05/10 08:32:57]

nit: It would probably make more sense to pass the dominator in here and get rid
of UpdateAllocationFoldingDominator.

[Hannes Payer (out of office), 2016/05/10 09:04:44]

Done.

+    flags_ = static_cast<HAllocate::Flags>(flags_ | ALLOCATION_FOLDED);
+    ClearFlag(kTrackSideEffectDominators);
+    ClearChangesFlag(kNewSpacePromotion);
+  }
+
+  bool IsAllocationFolded() { return (flags_ & ALLOCATION_FOLDED) != 0; }
+
   bool HandleSideEffectDominator(GVNFlag side_effect,
                                  HValue* dominator) override;
 
@@ -5026,23 +5033,19 @@ class HAllocate final : public HTemplateInstruction<2> {
     ALLOCATE_IN_OLD_SPACE = 1 << 2,
     ALLOCATE_DOUBLE_ALIGNED = 1 << 3,
     PREFILL_WITH_FILLER = 1 << 4,
-    CLEAR_NEXT_MAP_WORD = 1 << 5
+    ALLOCATION_FOLDING_DOMINATOR = 1 << 5,
+    ALLOCATION_FOLDED = 1 << 6
   };
 
-  HAllocate(HValue* context,
-            HValue* size,
-            HType type,
-            PretenureFlag pretenure_flag,
-            InstanceType instance_type,
-            Handle<AllocationSite> allocation_site =
-                Handle<AllocationSite>::null())
-      : HTemplateInstruction<2>(type),
-        flags_(ComputeFlags(pretenure_flag, instance_type)),
-        dominating_allocate_(NULL),
-        filler_free_space_size_(NULL),
-        size_upper_bound_(NULL) {
+  HAllocate(
+      HValue* context, HValue* size, HType type, PretenureFlag pretenure_flag,
+      InstanceType instance_type, HValue* dominator,
+      Handle<AllocationSite> allocation_site = Handle<AllocationSite>::null())
+      : HTemplateInstruction<3>(type),
+        flags_(ComputeFlags(pretenure_flag, instance_type)) {
     SetOperandAt(0, context);
     UpdateSize(size);
+    SetOperandAt(2, dominator);
     set_representation(Representation::Tagged());
     SetFlag(kTrackSideEffectDominators);
     SetChangesFlag(kNewSpacePromotion);
@@ -5072,46 +5075,24 @@ class HAllocate final : public HTemplateInstruction<2> {
     if (!FLAG_use_gvn || !FLAG_use_allocation_folding) {
       flags = static_cast<Flags>(flags | PREFILL_WITH_FILLER);
     }
-    if (pretenure_flag == NOT_TENURED &&
-        AllocationSite::CanTrack(instance_type)) {
-      flags = static_cast<Flags>(flags | CLEAR_NEXT_MAP_WORD);
-    }
     return flags;
   }
 
-  void UpdateClearNextMapWord(bool clear_next_map_word) {
-    flags_ = static_cast<Flags>(clear_next_map_word
-                                ? flags_ | CLEAR_NEXT_MAP_WORD
-                                : flags_ & ~CLEAR_NEXT_MAP_WORD);
-  }
-
   void UpdateSize(HValue* size) {
     SetOperandAt(1, size);
-    if (size->IsInteger32Constant()) {
-      size_upper_bound_ = HConstant::cast(size);
-    } else {
-      size_upper_bound_ = NULL;
-    }
   }
 
-  HAllocate* GetFoldableDominator(HAllocate* dominator);
-
-  void UpdateFreeSpaceFiller(int32_t filler_size);
-
-  void CreateFreeSpaceFiller(int32_t filler_size);
+  void UpdateAllocationFoldingDominator(HAllocate* dominator) {
+    SetOperandAt(2, dominator);
+  }
 
   bool IsFoldable(HAllocate* allocate) {
     return (IsNewSpaceAllocation() && allocate->IsNewSpaceAllocation()) ||
            (IsOldSpaceAllocation() && allocate->IsOldSpaceAllocation());
   }
 
-  void ClearNextMapWord(int offset);
-
   Flags flags_;
   Handle<Map> known_initial_map_;
-  HAllocate* dominating_allocate_;
-  HStoreNamedField* filler_free_space_size_;
-  HConstant* size_upper_bound_;
 };
 
 
@@ -5183,9 +5164,20 @@ inline bool StoringValueNeedsWriteBarrier(HValue* value) {
 inline bool ReceiverObjectNeedsWriteBarrier(HValue* object,
                                             HValue* value,
                                             HValue* dominator) {
+  // There may be multiple inner allocates dominated by one allocate.
   while (object->IsInnerAllocatedObject()) {
     object = HInnerAllocatedObject::cast(object)->base_object();
   }
+
+  if (object->IsAllocate()) {
+    HAllocate* allocate = HAllocate::cast(object);
+    if (allocate->IsAllocationFolded()) {
+      HValue* dominator = allocate->allocation_folding_dominator();

[Michael Lippautz, 2016/05/10 08:32:57]

nit: If you make this a nullptr check and not use an operand on HAllocate but a
regular field, you could remove all changes initializing a new HAllocate(?)

[Hannes Payer (out of office), 2016/05/10 09:04:44]

This is not possible. The input has to be a valid operation.

+      DCHECK(HAllocate::cast(dominator)->IsAllocationFoldingDominator());
+      object = dominator;
+    }
+  }
+
   if (object->IsConstant() &&
       HConstant::cast(object)->HasExternalReferenceValue()) {
     // Stores to external references require no write barriers