Improve inobject field tracking during GVN.

src/hydrogen-gvn.cc

Index: src/hydrogen-gvn.cc
diff --git a/src/hydrogen-gvn.cc b/src/hydrogen-gvn.cc
index bc836890bb136544c560474c222d7b354c9ddb4a..89765545185490d8130dcbf2822154c38037be94 100644
--- a/src/hydrogen-gvn.cc
+++ b/src/hydrogen-gvn.cc
@@ -32,39 +32,39 @@
 namespace v8 {
 namespace internal {
 
-class HValueMap: public ZoneObject {
+class HInstructionMap V8_FINAL : public ZoneObject {
  public:
-  explicit HValueMap(Zone* zone)
+  HInstructionMap(Zone* zone, SideEffectsScope* side_effects_scope)
       : array_size_(0),
         lists_size_(0),
         count_(0),
-        present_flags_(0),
         array_(NULL),
         lists_(NULL),
-        free_list_head_(kNil) {
+        free_list_head_(kNil),
+        side_effects_scope_(side_effects_scope) {
     ResizeLists(kInitialSize, zone);
     Resize(kInitialSize, zone);
   }
 
-  void Kill(GVNFlagSet flags);
+  void Kill(SideEffects side_effects);
 
-  void Add(HValue* value, Zone* zone) {
-    present_flags_.Add(value->gvn_flags());
-    Insert(value, zone);
+  void Add(HInstruction* instr, Zone* zone) {
+    present_depends_on_.Add(side_effects_scope_->ComputeDependsOn(instr));
+    Insert(instr, zone);
   }
 
-  HValue* Lookup(HValue* value) const;
+  HInstruction* Lookup(HInstruction* instr) const;
 
-  HValueMap* Copy(Zone* zone) const {
-    return new(zone) HValueMap(zone, this);
+  HInstructionMap* Copy(Zone* zone) const {
+    return new(zone) HInstructionMap(zone, this);
   }
 
   bool IsEmpty() const { return count_ == 0; }
 
  private:
-  // A linked list of HValue* values.  Stored in arrays.
-  struct HValueMapListElement {
-    HValue* value;
+  // A linked list of HInstruction* values.  Stored in arrays.
+  struct HInstructionMapListElement {
+    HInstruction* instr;
     int next;  // Index in the array of the next list element.
   };
   static const int kNil = -1;  // The end of a linked list
@@ -72,34 +72,36 @@ class HValueMap: public ZoneObject {
   // Must be a power of 2.
   static const int kInitialSize = 16;
 
-  HValueMap(Zone* zone, const HValueMap* other);
+  HInstructionMap(Zone* zone, const HInstructionMap* other);
 
   void Resize(int new_size, Zone* zone);
   void ResizeLists(int new_size, Zone* zone);
-  void Insert(HValue* value, Zone* zone);
+  void Insert(HInstruction* instr, Zone* zone);
   uint32_t Bound(uint32_t value) const { return value & (array_size_ - 1); }
 
   int array_size_;
   int lists_size_;
-  int count_;  // The number of values stored in the HValueMap.
-  GVNFlagSet present_flags_;  // All flags that are in any value in the
-                              // HValueMap.
-  HValueMapListElement* array_;  // Primary store - contains the first value
+  int count_;  // The number of values stored in the HInstructionMap.
+  SideEffects present_depends_on_;
+  HInstructionMapListElement* array_;
+  // Primary store - contains the first value
   // with a given hash.  Colliding elements are stored in linked lists.
-  HValueMapListElement* lists_;  // The linked lists containing hash collisions.
+  HInstructionMapListElement* lists_;
+  // The linked lists containing hash collisions.
   int free_list_head_;  // Unused elements in lists_ are on the free list.
+  SideEffectsScope* side_effects_scope_;
 };
 
 
-class HSideEffectMap BASE_EMBEDDED {
+class HSideEffectMap V8_FINAL BASE_EMBEDDED {
  public:
   HSideEffectMap();
   explicit HSideEffectMap(HSideEffectMap* other);
   HSideEffectMap& operator= (const HSideEffectMap& other);
 
-  void Kill(GVNFlagSet flags);
+  void Kill(SideEffects side_effects);
 
-  void Store(GVNFlagSet flags, HInstruction* instr);
+  void Store(SideEffects side_effects, HInstruction* instr);
 
   bool IsEmpty() const { return count_ == 0; }
 
@@ -152,35 +154,36 @@ void TraceGVN(const char* msg, ...) {
   }
 
 
-HValueMap::HValueMap(Zone* zone, const HValueMap* other)
+HInstructionMap::HInstructionMap(Zone* zone, const HInstructionMap* other)
     : array_size_(other->array_size_),
       lists_size_(other->lists_size_),
       count_(other->count_),
-      present_flags_(other->present_flags_),
-      array_(zone->NewArray<HValueMapListElement>(other->array_size_)),
-      lists_(zone->NewArray<HValueMapListElement>(other->lists_size_)),
-      free_list_head_(other->free_list_head_) {
+      present_depends_on_(other->present_depends_on_),
+      array_(zone->NewArray<HInstructionMapListElement>(other->array_size_)),
+      lists_(zone->NewArray<HInstructionMapListElement>(other->lists_size_)),
+      free_list_head_(other->free_list_head_),
+      side_effects_scope_(other->side_effects_scope_) {
   OS::MemCopy(
-      array_, other->array_, array_size_ * sizeof(HValueMapListElement));
+      array_, other->array_, array_size_ * sizeof(HInstructionMapListElement));
   OS::MemCopy(
-      lists_, other->lists_, lists_size_ * sizeof(HValueMapListElement));
+      lists_, other->lists_, lists_size_ * sizeof(HInstructionMapListElement));
 }
 
 
-void HValueMap::Kill(GVNFlagSet flags) {
-  GVNFlagSet depends_flags = HValue::ConvertChangesToDependsFlags(flags);
-  if (!present_flags_.ContainsAnyOf(depends_flags)) return;
-  present_flags_.RemoveAll();
+void HInstructionMap::Kill(SideEffects changes) {
+  if (!present_depends_on_.ContainsAnyOf(changes)) return;
+  present_depends_on_.RemoveAll();
   for (int i = 0; i < array_size_; ++i) {
-    HValue* value = array_[i].value;
-    if (value != NULL) {
+    HInstruction* instr = array_[i].instr;
+    if (instr != NULL) {
       // Clear list of collisions first, so we know if it becomes empty.
       int kept = kNil;  // List of kept elements.
       int next;
       for (int current = array_[i].next; current != kNil; current = next) {
         next = lists_[current].next;
-        HValue* value = lists_[current].value;
-        if (value->gvn_flags().ContainsAnyOf(depends_flags)) {
+        HInstruction* instr = lists_[current].instr;
+        SideEffects depends_on = side_effects_scope_->ComputeDependsOn(instr);
+        if (depends_on.ContainsAnyOf(changes)) {
           // Drop it.
           count_--;
           lists_[current].next = free_list_head_;
@@ -189,40 +192,41 @@ void HValueMap::Kill(GVNFlagSet flags) {
           // Keep it.
           lists_[current].next = kept;
           kept = current;
-          present_flags_.Add(value->gvn_flags());
+          present_depends_on_.Add(depends_on);
         }
       }
       array_[i].next = kept;
 
       // Now possibly drop directly indexed element.
-      value = array_[i].value;
-      if (value->gvn_flags().ContainsAnyOf(depends_flags)) {  // Drop it.
+      instr = array_[i].instr;
+      SideEffects depends_on = side_effects_scope_->ComputeDependsOn(instr);
+      if (depends_on.ContainsAnyOf(changes)) {  // Drop it.
         count_--;
         int head = array_[i].next;
         if (head == kNil) {
-          array_[i].value = NULL;
+          array_[i].instr = NULL;
         } else {
-          array_[i].value = lists_[head].value;
+          array_[i].instr = lists_[head].instr;
           array_[i].next = lists_[head].next;
           lists_[head].next = free_list_head_;
           free_list_head_ = head;
         }
       } else {
-        present_flags_.Add(value->gvn_flags());  // Keep it.
+        present_depends_on_.Add(depends_on);  // Keep it.
       }
     }
   }
 }
 
 
-HValue* HValueMap::Lookup(HValue* value) const {
-  uint32_t hash = static_cast<uint32_t>(value->Hashcode());
+HInstruction* HInstructionMap::Lookup(HInstruction* instr) const {
+  uint32_t hash = static_cast<uint32_t>(instr->Hashcode());
   uint32_t pos = Bound(hash);
-  if (array_[pos].value != NULL) {
-    if (array_[pos].value->Equals(value)) return array_[pos].value;
+  if (array_[pos].instr != NULL) {
+    if (array_[pos].instr->Equals(instr)) return array_[pos].instr;
     int next = array_[pos].next;
     while (next != kNil) {
-      if (lists_[next].value->Equals(value)) return lists_[next].value;
+      if (lists_[next].instr->Equals(instr)) return lists_[next].instr;
       next = lists_[next].next;
     }
   }
@@ -230,7 +234,7 @@ HValue* HValueMap::Lookup(HValue* value) const {
 }
 
 
-void HValueMap::Resize(int new_size, Zone* zone) {
+void HInstructionMap::Resize(int new_size, Zone* zone) {
   ASSERT(new_size > count_);
   // Hashing the values into the new array has no more collisions than in the
   // old hash map, so we can use the existing lists_ array, if we are careful.
@@ -240,33 +244,33 @@ void HValueMap::Resize(int new_size, Zone* zone) {
     ResizeLists(lists_size_ << 1, zone);
   }
 
-  HValueMapListElement* new_array =
-      zone->NewArray<HValueMapListElement>(new_size);
-  memset(new_array, 0, sizeof(HValueMapListElement) * new_size);
+  HInstructionMapListElement* new_array =
+      zone->NewArray<HInstructionMapListElement>(new_size);
+  memset(new_array, 0, sizeof(HInstructionMapListElement) * new_size);
 
-  HValueMapListElement* old_array = array_;
+  HInstructionMapListElement* old_array = array_;
   int old_size = array_size_;
 
   int old_count = count_;
   count_ = 0;
-  // Do not modify present_flags_.  It is currently correct.
+  // Do not modify present_depends_on_.  It is currently correct.
   array_size_ = new_size;
   array_ = new_array;
 
   if (old_array != NULL) {
     // Iterate over all the elements in lists, rehashing them.
     for (int i = 0; i < old_size; ++i) {
-      if (old_array[i].value != NULL) {
+      if (old_array[i].instr != NULL) {
         int current = old_array[i].next;
         while (current != kNil) {
-          Insert(lists_[current].value, zone);
+          Insert(lists_[current].instr, zone);
           int next = lists_[current].next;
           lists_[current].next = free_list_head_;
           free_list_head_ = current;
           current = next;
         }
-        // Rehash the directly stored value.
-        Insert(old_array[i].value, zone);
+        // Rehash the directly stored instruction.
+        Insert(old_array[i].instr, zone);
       }
     }
   }
@@ -275,21 +279,22 @@ void HValueMap::Resize(int new_size, Zone* zone) {
 }
 
 
-void HValueMap::ResizeLists(int new_size, Zone* zone) {
+void HInstructionMap::ResizeLists(int new_size, Zone* zone) {
   ASSERT(new_size > lists_size_);
 
-  HValueMapListElement* new_lists =
-      zone->NewArray<HValueMapListElement>(new_size);
-  memset(new_lists, 0, sizeof(HValueMapListElement) * new_size);
+  HInstructionMapListElement* new_lists =
+      zone->NewArray<HInstructionMapListElement>(new_size);
+  memset(new_lists, 0, sizeof(HInstructionMapListElement) * new_size);
 
-  HValueMapListElement* old_lists = lists_;
+  HInstructionMapListElement* old_lists = lists_;
   int old_size = lists_size_;
 
   lists_size_ = new_size;
   lists_ = new_lists;
 
   if (old_lists != NULL) {
-    OS::MemCopy(lists_, old_lists, old_size * sizeof(HValueMapListElement));
+    OS::MemCopy(
+        lists_, old_lists, old_size * sizeof(HInstructionMapListElement));
   }
   for (int i = old_size; i < lists_size_; ++i) {
     lists_[i].next = free_list_head_;
@@ -298,15 +303,15 @@ void HValueMap::ResizeLists(int new_size, Zone* zone) {
 }
 
 
-void HValueMap::Insert(HValue* value, Zone* zone) {
-  ASSERT(value != NULL);
+void HInstructionMap::Insert(HInstruction* instr, Zone* zone) {
+  ASSERT(instr != NULL);
   // Resizing when half of the hashtable is filled up.
   if (count_ >= array_size_ >> 1) Resize(array_size_ << 1, zone);
   ASSERT(count_ < array_size_);
   count_++;
-  uint32_t pos = Bound(static_cast<uint32_t>(value->Hashcode()));
-  if (array_[pos].value == NULL) {
-    array_[pos].value = value;
+  uint32_t pos = Bound(static_cast<uint32_t>(instr->Hashcode()));
+  if (array_[pos].instr == NULL) {
+    array_[pos].instr = instr;
     array_[pos].next = kNil;
   } else {
     if (free_list_head_ == kNil) {
@@ -315,9 +320,9 @@ void HValueMap::Insert(HValue* value, Zone* zone) {
     int new_element_pos = free_list_head_;
     ASSERT(new_element_pos != kNil);
     free_list_head_ = lists_[free_list_head_].next;
-    lists_[new_element_pos].value = value;
+    lists_[new_element_pos].instr = instr;
     lists_[new_element_pos].next = array_[pos].next;
-    ASSERT(array_[pos].next == kNil || lists_[array_[pos].next].value != NULL);
+    ASSERT(array_[pos].next == kNil || lists_[array_[pos].next].instr != NULL);
     array_[pos].next = new_element_pos;
   }
 }
@@ -341,10 +346,9 @@ HSideEffectMap& HSideEffectMap::operator= (const HSideEffectMap& other) {
 }
 
 
-void HSideEffectMap::Kill(GVNFlagSet flags) {
+void HSideEffectMap::Kill(SideEffects side_effects) {
   for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
-    GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
-    if (flags.Contains(changes_flag)) {
+    if (side_effects.ContainsFlag(GVNFlagFromInt(i))) {
       if (data_[i] != NULL) count_--;
       data_[i] = NULL;
     }
@@ -352,10 +356,9 @@ void HSideEffectMap::Kill(GVNFlagSet flags) {
 }
 
 
-void HSideEffectMap::Store(GVNFlagSet flags, HInstruction* instr) {
+void HSideEffectMap::Store(SideEffects side_effects, HInstruction* instr) {
   for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
-    GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
-    if (flags.Contains(changes_flag)) {
+    if (side_effects.ContainsFlag(GVNFlagFromInt(i))) {
       if (data_[i] == NULL) count_++;
       data_[i] = instr;
     }
@@ -363,6 +366,95 @@ void HSideEffectMap::Store(GVNFlagSet flags, HInstruction* instr) {
 }
 
 
+SideEffects SideEffectsScope::ComputeChanges(HInstruction* instr) {
+  SideEffects result(instr->ChangesFlags());
+  if (result.ContainsFlag(kInobjectFields)) {
+    int index;
+    if (instr->IsStoreNamedField() &&
+        ComputeInobjectField(HStoreNamedField::cast(instr)->access(), &index)) {
+      result.RemoveFlag(kInobjectFields);
+      result.AddSpecial(index);
+    } else {
+      result.AddAllSpecial();
+    }
+  }
+  return result;
+}
+
+
+SideEffects SideEffectsScope::ComputeDependsOn(HInstruction* instr) {
+  SideEffects result(instr->DependsOnFlags());
+  if (result.ContainsFlag(kInobjectFields)) {
+    int index;
+    if (instr->IsLoadNamedField() &&
+        ComputeInobjectField(HLoadNamedField::cast(instr)->access(), &index)) {
+      result.RemoveFlag(kInobjectFields);
+      result.AddSpecial(index);
+    } else {
+      result.AddAllSpecial();
+    }
+  }
+  return result;
+}
+
+
+void SideEffectsScope::PrintSideEffectsTo(StringStream* stream,
+                                          SideEffects side_effects) const {
+  const char* separator = "";
+  stream->Add("[");
+  for (int bit = 0; bit < kNumberOfFlags; ++bit) {
+    GVNFlag flag = GVNFlagFromInt(bit);
+    if (side_effects.ContainsFlag(flag)) {
+      stream->Add(separator);
+      separator = ", ";
+      switch (flag) {
+#define DECLARE_FLAG(Type)      \
+        case k##Type:           \
+          stream->Add(#Type);   \
+          break;
+GVN_TRACKED_FLAG_LIST(DECLARE_FLAG)
+GVN_UNTRACKED_FLAG_LIST(DECLARE_FLAG)
+#undef DECLARE_FLAG
+        default:
+            break;
+      }
+    }
+  }
+  for (int index = 0; index < num_inobject_fields_; ++index) {
+    if (side_effects.ContainsSpecial(index)) {
+      stream->Add(separator);
+      separator = ", ";
+      inobject_fields_[index].PrintTo(stream);
+    }
+  }
+  stream->Add("]");
+}
+
+
+bool SideEffectsScope::ComputeInobjectField(HObjectAccess access, int* index) {
+  for (int i = 0; i < num_inobject_fields_; ++i) {
+    if (access.Equals(inobject_fields_[i])) {
+      *index = i;
+      return true;
+    }
+  }
+  if (num_inobject_fields_ < SideEffects::kNumberOfSpecials) {
+    if (FLAG_trace_gvn) {
+      HeapStringAllocator allocator;
+      StringStream stream(&allocator);
+      stream.Add("Recording inobject field access ");
+      access.PrintTo(&stream);
+      stream.Add(" (mapped to special index %d)\n", num_inobject_fields_);
+      stream.OutputToStdOut();
+    }
+    *index = num_inobject_fields_;
+    inobject_fields_[num_inobject_fields_++] = access;
+    return true;
+  }
+  return false;
+}
+
+
 HGlobalValueNumberingPhase::HGlobalValueNumberingPhase(HGraph* graph)
     : HPhase("H_Global value numbering", graph),
       removed_side_effects_(false),
@@ -370,10 +462,10 @@ HGlobalValueNumberingPhase::HGlobalValueNumberingPhase(HGraph* graph)
       loop_side_effects_(graph->blocks()->length(), zone()),
       visited_on_paths_(graph->blocks()->length(), zone()) {
   ASSERT(!AllowHandleAllocation::IsAllowed());
-  block_side_effects_.AddBlock(GVNFlagSet(), graph->blocks()->length(),
-                                zone());
-  loop_side_effects_.AddBlock(GVNFlagSet(), graph->blocks()->length(),
-                              zone());
+  block_side_effects_.AddBlock(
+      SideEffects(), graph->blocks()->length(), zone());
+  loop_side_effects_.AddBlock(
+      SideEffects(), graph->blocks()->length(), zone());
 }
 
 
@@ -409,12 +501,12 @@ void HGlobalValueNumberingPhase::ComputeBlockSideEffects() {
   for (int i = graph()->blocks()->length() - 1; i >= 0; --i) {
     // Compute side effects for the block.
     HBasicBlock* block = graph()->blocks()->at(i);
-    GVNFlagSet side_effects;
+    SideEffects side_effects;
     if (block->IsReachable() && !block->IsDeoptimizing()) {
       int id = block->block_id();
       for (HInstructionIterator it(block); !it.Done(); it.Advance()) {
         HInstruction* instr = it.Current();
-        side_effects.Add(instr->ChangesFlags());
+        side_effects.Add(side_effects_scope_.ComputeChanges(instr));
       }
       block_side_effects_[id].Add(side_effects);
 
@@ -438,103 +530,22 @@ void HGlobalValueNumberingPhase::ComputeBlockSideEffects() {
 }
 
 
-SmartArrayPointer<char> GetGVNFlagsString(GVNFlagSet flags) {
-  char underlying_buffer[kNumberOfFlags * 128];
-  Vector<char> buffer(underlying_buffer, sizeof(underlying_buffer));
-#if DEBUG
-  int offset = 0;
-  const char* separator = "";
-  const char* comma = ", ";
-  buffer[0] = 0;
-  uint32_t set_depends_on = 0;
-  uint32_t set_changes = 0;
-  for (int bit = 0; bit < kNumberOfFlags; ++bit) {
-    if (flags.Contains(static_cast<GVNFlag>(bit))) {
-      if (bit % 2 == 0) {
-        set_changes++;
-      } else {
-        set_depends_on++;
-      }
-    }
-  }
-  bool positive_changes = set_changes < (kNumberOfFlags / 2);
-  bool positive_depends_on = set_depends_on < (kNumberOfFlags / 2);
-  if (set_changes > 0) {
-    if (positive_changes) {
-      offset += OS::SNPrintF(buffer + offset, "changes [");
-    } else {
-      offset += OS::SNPrintF(buffer + offset, "changes all except [");
-    }
-    for (int bit = 0; bit < kNumberOfFlags; ++bit) {
-      if (flags.Contains(static_cast<GVNFlag>(bit)) == positive_changes) {
-        switch (static_cast<GVNFlag>(bit)) {
-#define DECLARE_FLAG(type)                                       \
-          case kChanges##type:                                   \
-            offset += OS::SNPrintF(buffer + offset, separator);  \
-            offset += OS::SNPrintF(buffer + offset, #type);      \
-            separator = comma;                                   \
-            break;
-GVN_TRACKED_FLAG_LIST(DECLARE_FLAG)
-GVN_UNTRACKED_FLAG_LIST(DECLARE_FLAG)
-#undef DECLARE_FLAG
-          default:
-              break;
-        }
-      }
-    }
-    offset += OS::SNPrintF(buffer + offset, "]");
-  }
-  if (set_depends_on > 0) {
-    separator = "";
-    if (set_changes > 0) {
-      offset += OS::SNPrintF(buffer + offset, ", ");
-    }
-    if (positive_depends_on) {
-      offset += OS::SNPrintF(buffer + offset, "depends on [");
-    } else {
-      offset += OS::SNPrintF(buffer + offset, "depends on all except [");
-    }
-    for (int bit = 0; bit < kNumberOfFlags; ++bit) {
-      if (flags.Contains(static_cast<GVNFlag>(bit)) == positive_depends_on) {
-        switch (static_cast<GVNFlag>(bit)) {
-#define DECLARE_FLAG(type)                                       \
-          case kDependsOn##type:                                 \
-            offset += OS::SNPrintF(buffer + offset, separator);  \
-            offset += OS::SNPrintF(buffer + offset, #type);      \
-            separator = comma;                                   \
-            break;
-GVN_TRACKED_FLAG_LIST(DECLARE_FLAG)
-GVN_UNTRACKED_FLAG_LIST(DECLARE_FLAG)
-#undef DECLARE_FLAG
-          default:
-            break;
-        }
-      }
-    }
-    offset += OS::SNPrintF(buffer + offset, "]");
-  }
-#else
-  OS::SNPrintF(buffer, "0x%08X", flags.ToIntegral());
-#endif
-  size_t string_len = strlen(underlying_buffer) + 1;
-  ASSERT(string_len <= sizeof(underlying_buffer));
-  char* result = new char[strlen(underlying_buffer) + 1];
-  OS::MemCopy(result, underlying_buffer, string_len);
-  return SmartArrayPointer<char>(result);
-}
-
-
 void HGlobalValueNumberingPhase::LoopInvariantCodeMotion() {
   TRACE_GVN_1("Using optimistic loop invariant code motion: %s\n",
               graph()->use_optimistic_licm() ? "yes" : "no");
   for (int i = graph()->blocks()->length() - 1; i >= 0; --i) {
     HBasicBlock* block = graph()->blocks()->at(i);
     if (block->IsLoopHeader()) {
-      GVNFlagSet side_effects = loop_side_effects_[block->block_id()];
-      TRACE_GVN_2("Try loop invariant motion for block B%d %s\n",
-                  block->block_id(),
-                  GetGVNFlagsString(side_effects).get());
-
+      SideEffects side_effects = loop_side_effects_[block->block_id()];
+      if (FLAG_trace_gvn) {
+        HeapStringAllocator allocator;
+        StringStream stream(&allocator);
+        stream.Add("Try loop invariant motion for block B%d changes ",
+                   block->block_id());
+        side_effects_scope_.PrintSideEffectsTo(&stream, side_effects);
+        stream.Add("\n");
+        stream.OutputToStdOut();
+      }
       HBasicBlock* last = block->loop_information()->GetLastBackEdge();
       for (int j = block->block_id(); j <= last->block_id(); ++j) {
         ProcessLoopBlock(graph()->blocks()->at(j), block, side_effects);
@@ -547,22 +558,37 @@ void HGlobalValueNumberingPhase::LoopInvariantCodeMotion() {
 void HGlobalValueNumberingPhase::ProcessLoopBlock(
     HBasicBlock* block,
     HBasicBlock* loop_header,
-    GVNFlagSet loop_kills) {
+    SideEffects loop_kills) {
   HBasicBlock* pre_header = loop_header->predecessors()->at(0);
-  GVNFlagSet depends_flags = HValue::ConvertChangesToDependsFlags(loop_kills);
-  TRACE_GVN_2("Loop invariant motion for B%d %s\n",
-              block->block_id(),
-              GetGVNFlagsString(depends_flags).get());
+  if (FLAG_trace_gvn) {
+    HeapStringAllocator allocator;
+    StringStream stream(&allocator);
+    stream.Add("Loop invariant code motion for B%d depends on ",
+               block->block_id());
+    side_effects_scope_.PrintSideEffectsTo(&stream, loop_kills);
+    stream.Add("\n");
+    stream.OutputToStdOut();
+  }
   HInstruction* instr = block->first();
   while (instr != NULL) {
     HInstruction* next = instr->next();
     if (instr->CheckFlag(HValue::kUseGVN)) {
-      TRACE_GVN_4("Checking instruction %d (%s) %s. Loop %s\n",
-                  instr->id(),
-                  instr->Mnemonic(),
-                  GetGVNFlagsString(instr->gvn_flags()).get(),
-                  GetGVNFlagsString(loop_kills).get());
-      bool can_hoist = !instr->gvn_flags().ContainsAnyOf(depends_flags);
+      SideEffects changes = side_effects_scope_.ComputeChanges(instr);
+      SideEffects depends_on = side_effects_scope_.ComputeDependsOn(instr);
+      if (FLAG_trace_gvn) {
+        HeapStringAllocator allocator;
+        StringStream stream(&allocator);
+        stream.Add("Checking instruction i%d (%s) changes ",
+                   instr->id(), instr->Mnemonic());
+        side_effects_scope_.PrintSideEffectsTo(&stream, changes);
+        stream.Add(", depends on ");
+        side_effects_scope_.PrintSideEffectsTo(&stream, depends_on);
+        stream.Add(". Loop changes ");
+        side_effects_scope_.PrintSideEffectsTo(&stream, loop_kills);
+        stream.Add("\n");
+        stream.OutputToStdOut();
+      }
+      bool can_hoist = !depends_on.ContainsAnyOf(loop_kills);
       if (can_hoist && !graph()->use_optimistic_licm()) {
         can_hoist = block->IsLoopSuccessorDominator();
       }
@@ -604,10 +630,10 @@ bool HGlobalValueNumberingPhase::ShouldMove(HInstruction* instr,
 }
 
 
-GVNFlagSet
+SideEffects
 HGlobalValueNumberingPhase::CollectSideEffectsOnPathsToDominatedBlock(
     HBasicBlock* dominator, HBasicBlock* dominated) {
-  GVNFlagSet side_effects;
+  SideEffects side_effects;
   for (int i = 0; i < dominated->predecessors()->length(); ++i) {
     HBasicBlock* block = dominated->predecessors()->at(i);
     if (dominator->block_id() < block->block_id() &&
@@ -636,13 +662,13 @@ class GvnBasicBlockState: public ZoneObject {
  public:
   static GvnBasicBlockState* CreateEntry(Zone* zone,
                                          HBasicBlock* entry_block,
-                                         HValueMap* entry_map) {
+                                         HInstructionMap* entry_map) {
     return new(zone)
         GvnBasicBlockState(NULL, entry_block, entry_map, NULL, zone);
   }
 
   HBasicBlock* block() { return block_; }
-  HValueMap* map() { return map_; }
+  HInstructionMap* map() { return map_; }
   HSideEffectMap* dominators() { return &dominators_; }
 
   GvnBasicBlockState* next_in_dominator_tree_traversal(
@@ -669,7 +695,7 @@ class GvnBasicBlockState: public ZoneObject {
 
  private:
   void Initialize(HBasicBlock* block,
-                  HValueMap* map,
+                  HInstructionMap* map,
                   HSideEffectMap* dominators,
                   bool copy_map,
                   Zone* zone) {
@@ -685,7 +711,7 @@ class GvnBasicBlockState: public ZoneObject {
 
   GvnBasicBlockState(GvnBasicBlockState* previous,
                      HBasicBlock* block,
-                     HValueMap* map,
+                     HInstructionMap* map,
                      HSideEffectMap* dominators,
                      Zone* zone)
       : previous_(previous), next_(NULL) {
@@ -732,7 +758,7 @@ class GvnBasicBlockState: public ZoneObject {
   GvnBasicBlockState* previous_;
   GvnBasicBlockState* next_;
   HBasicBlock* block_;
-  HValueMap* map_;
+  HInstructionMap* map_;
   HSideEffectMap dominators_;
   int dominated_index_;
   int length_;
@@ -745,13 +771,14 @@ class GvnBasicBlockState: public ZoneObject {
 // GvnBasicBlockState instances.
 void HGlobalValueNumberingPhase::AnalyzeGraph() {
   HBasicBlock* entry_block = graph()->entry_block();
-  HValueMap* entry_map = new(zone()) HValueMap(zone());
+  HInstructionMap* entry_map =
+      new(zone()) HInstructionMap(zone(), &side_effects_scope_);
   GvnBasicBlockState* current =
       GvnBasicBlockState::CreateEntry(zone(), entry_block, entry_map);
 
   while (current != NULL) {
     HBasicBlock* block = current->block();
-    HValueMap* map = current->map();
+    HInstructionMap* map = current->map();
     HSideEffectMap* dominators = current->dominators();
 
     TRACE_GVN_2("Analyzing block B%d%s\n",
@@ -770,17 +797,15 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
       if (instr->CheckFlag(HValue::kTrackSideEffectDominators)) {
         for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
           HValue* other = dominators->at(i);
-          GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
-          GVNFlag depends_on_flag = HValue::DependsOnFlagFromInt(i);
-          if (instr->DependsOnFlags().Contains(depends_on_flag) &&
-              (other != NULL)) {
+          GVNFlag flag = GVNFlagFromInt(i);
+          if (instr->DependsOnFlags().Contains(flag) && other != NULL) {
             TRACE_GVN_5("Side-effect #%d in %d (%s) is dominated by %d (%s)\n",
                         i,
                         instr->id(),
                         instr->Mnemonic(),
                         other->id(),
                         other->Mnemonic());
-            if (instr->HandleSideEffectDominator(changes_flag, other)) {
+            if (instr->HandleSideEffectDominator(flag, other)) {
               removed_side_effects_ = true;
             }
           }
@@ -789,21 +814,27 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
       // Instruction was unlinked during graph traversal.
       if (!instr->IsLinked()) continue;
 
-      GVNFlagSet flags = instr->ChangesFlags();
-      if (!flags.IsEmpty()) {
+      SideEffects changes = side_effects_scope_.ComputeChanges(instr);
+      if (!changes.IsEmpty()) {
         // Clear all instructions in the map that are affected by side effects.
         // Store instruction as the dominating one for tracked side effects.
-        map->Kill(flags);
-        dominators->Store(flags, instr);
-        TRACE_GVN_2("Instruction %d %s\n", instr->id(),
-                    GetGVNFlagsString(flags).get());
+        map->Kill(changes);
+        dominators->Store(changes, instr);
+        if (FLAG_trace_gvn) {
+          HeapStringAllocator allocator;
+          StringStream stream(&allocator);
+          stream.Add("Instruction i%d changes ", instr->id());
+          side_effects_scope_.PrintSideEffectsTo(&stream, changes);
+          stream.Add("\n");
+          stream.OutputToStdOut();
+        }
       }
       if (instr->CheckFlag(HValue::kUseGVN)) {
         ASSERT(!instr->HasObservableSideEffects());
-        HValue* other = map->Lookup(instr);
+        HInstruction* other = map->Lookup(instr);
         if (other != NULL) {
           ASSERT(instr->Equals(other) && other->Equals(instr));
-          TRACE_GVN_4("Replacing value %d (%s) with value %d (%s)\n",
+          TRACE_GVN_4("Replacing instruction i%d (%s) with i%d (%s)\n",
                       instr->id(),
                       instr->Mnemonic(),
                       other->id(),
@@ -823,7 +854,7 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
 
     if (next != NULL) {
       HBasicBlock* dominated = next->block();
-      HValueMap* successor_map = next->map();
+      HInstructionMap* successor_map = next->map();
       HSideEffectMap* successor_dominators = next->dominators();
 
       // Kill everything killed on any path between this block and the
@@ -834,7 +865,7 @@ void HGlobalValueNumberingPhase::AnalyzeGraph() {
       if ((!successor_map->IsEmpty() || !successor_dominators->IsEmpty()) &&
           dominator_block->block_id() + 1 < dominated->block_id()) {
         visited_on_paths_.Clear();
-        GVNFlagSet side_effects_on_all_paths =
+        SideEffects side_effects_on_all_paths =
             CollectSideEffectsOnPathsToDominatedBlock(dominator_block,
                                                       dominated);
         successor_map->Kill(side_effects_on_all_paths);