[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 196a14fc705533c86e6cbf1ccf1ae10941606ee4..2fad18085e5c10cd69b59c0310ee79a8c6bd1480 100644
--- a/src/crankshaft/hydrogen-instructions.h
+++ b/src/crankshaft/hydrogen-instructions.h
@@ -5005,14 +5005,30 @@ 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 MakeAllocationFoldingDominated() {
+    flags_ =
+        static_cast<HAllocate::Flags>(flags_ | ALLOCATION_FOLDING_DOMINATED);
+    ClearFlag(kTrackSideEffectDominators);
+    ClearChangesFlag(kNewSpacePromotion);
+  }
+
+  bool IsAllocationFoldingDominated() {
+    return (flags_ & ALLOCATION_FOLDING_DOMINATED) != 0;
+  }
+
   bool HandleSideEffectDominator(GVNFlag side_effect,
                                  HValue* dominator) override;
 
@@ -5026,7 +5042,8 @@ 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_FOLDING_DOMINATED = 1 << 6

[Benedikt Meurer, 2016/04/19 07:25:38]

Is there a better name than "dominated"?

[Hannes Payer (out of office), 2016/04/19 11:03:56]

Changed to ALLOCATION_FOLDED. Done.

   };
 
   HAllocate(HValue* context,
@@ -5072,19 +5089,9 @@ 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()) {
@@ -5096,17 +5103,11 @@ class HAllocate final : public HTemplateInstruction<2> {
 
   HAllocate* GetFoldableDominator(HAllocate* dominator);
 
-  void UpdateFreeSpaceFiller(int32_t filler_size);
-
-  void CreateFreeSpaceFiller(int32_t filler_size);
-
   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_;