Extract GlobalValueNumberer and helper classes from hydrogen.cc and move to hydrogen-gvn.cc.

src/hydrogen.cc

Index: src/hydrogen.cc
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 0ee6e53cfae3b9fef849c44373bee290b3cd07df..40a7e3a16f9cf95cbe5bedad7d4232c50321f37f 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -26,6 +26,7 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "hydrogen.h"
+#include "hydrogen-gvn.h"
 
 #include <algorithm>
 
@@ -2757,251 +2758,6 @@ void HRangeAnalysis::AddRange(HValue* value, Range* range) {
 }
 
 
-void TraceGVN(const char* msg, ...) {
-  va_list arguments;
-  va_start(arguments, msg);
-  OS::VPrint(msg, arguments);
-  va_end(arguments);
-}
-
-// Wrap TraceGVN in macros to avoid the expense of evaluating its arguments when
-// --trace-gvn is off.
-#define TRACE_GVN_1(msg, a1)                    \
-  if (FLAG_trace_gvn) {                         \
-    TraceGVN(msg, a1);                          \
-  }
-
-#define TRACE_GVN_2(msg, a1, a2)                \
-  if (FLAG_trace_gvn) {                         \
-    TraceGVN(msg, a1, a2);                      \
-  }
-
-#define TRACE_GVN_3(msg, a1, a2, a3)            \
-  if (FLAG_trace_gvn) {                         \
-    TraceGVN(msg, a1, a2, a3);                  \
-  }
-
-#define TRACE_GVN_4(msg, a1, a2, a3, a4)        \
-  if (FLAG_trace_gvn) {                         \
-    TraceGVN(msg, a1, a2, a3, a4);              \
-  }
-
-#define TRACE_GVN_5(msg, a1, a2, a3, a4, a5)    \
-  if (FLAG_trace_gvn) {                         \
-    TraceGVN(msg, a1, a2, a3, a4, a5);          \
-  }
-
-
-HValueMap::HValueMap(Zone* zone, const HValueMap* 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_) {
-  OS::MemCopy(
-      array_, other->array_, array_size_ * sizeof(HValueMapListElement));
-  OS::MemCopy(
-      lists_, other->lists_, lists_size_ * sizeof(HValueMapListElement));
-}
-
-
-void HValueMap::Kill(GVNFlagSet flags) {
-  GVNFlagSet depends_flags = HValue::ConvertChangesToDependsFlags(flags);
-  if (!present_flags_.ContainsAnyOf(depends_flags)) return;
-  present_flags_.RemoveAll();
-  for (int i = 0; i < array_size_; ++i) {
-    HValue* value = array_[i].value;
-    if (value != 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)) {
-          // Drop it.
-          count_--;
-          lists_[current].next = free_list_head_;
-          free_list_head_ = current;
-        } else {
-          // Keep it.
-          lists_[current].next = kept;
-          kept = current;
-          present_flags_.Add(value->gvn_flags());
-        }
-      }
-      array_[i].next = kept;
-
-      // Now possibly drop directly indexed element.
-      value = array_[i].value;
-      if (value->gvn_flags().ContainsAnyOf(depends_flags)) {  // Drop it.
-        count_--;
-        int head = array_[i].next;
-        if (head == kNil) {
-          array_[i].value = NULL;
-        } else {
-          array_[i].value = lists_[head].value;
-          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.
-      }
-    }
-  }
-}
-
-
-HValue* HValueMap::Lookup(HValue* value) const {
-  uint32_t hash = static_cast<uint32_t>(value->Hashcode());
-  uint32_t pos = Bound(hash);
-  if (array_[pos].value != NULL) {
-    if (array_[pos].value->Equals(value)) return array_[pos].value;
-    int next = array_[pos].next;
-    while (next != kNil) {
-      if (lists_[next].value->Equals(value)) return lists_[next].value;
-      next = lists_[next].next;
-    }
-  }
-  return NULL;
-}
-
-
-void HValueMap::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.
-
-  // Make sure we have at least one free element.
-  if (free_list_head_ == kNil) {
-    ResizeLists(lists_size_ << 1, zone);
-  }
-
-  HValueMapListElement* new_array =
-      zone->NewArray<HValueMapListElement>(new_size);
-  memset(new_array, 0, sizeof(HValueMapListElement) * new_size);
-
-  HValueMapListElement* old_array = array_;
-  int old_size = array_size_;
-
-  int old_count = count_;
-  count_ = 0;
-  // Do not modify present_flags_.  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) {
-        int current = old_array[i].next;
-        while (current != kNil) {
-          Insert(lists_[current].value, 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);
-      }
-    }
-  }
-  USE(old_count);
-  ASSERT(count_ == old_count);
-}
-
-
-void HValueMap::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);
-
-  HValueMapListElement* 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));
-  }
-  for (int i = old_size; i < lists_size_; ++i) {
-    lists_[i].next = free_list_head_;
-    free_list_head_ = i;
-  }
-}
-
-
-void HValueMap::Insert(HValue* value, Zone* zone) {
-  ASSERT(value != 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;
-    array_[pos].next = kNil;
-  } else {
-    if (free_list_head_ == kNil) {
-      ResizeLists(lists_size_ << 1, 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].next = array_[pos].next;
-    ASSERT(array_[pos].next == kNil || lists_[array_[pos].next].value != NULL);
-    array_[pos].next = new_element_pos;
-  }
-}
-
-
-HSideEffectMap::HSideEffectMap() : count_(0) {
-  memset(data_, 0, kNumberOfTrackedSideEffects * kPointerSize);
-}
-
-
-HSideEffectMap::HSideEffectMap(HSideEffectMap* other) : count_(other->count_) {
-  *this = *other;  // Calls operator=.
-}
-
-
-HSideEffectMap& HSideEffectMap::operator= (const HSideEffectMap& other) {
-  if (this != &other) {
-    OS::MemCopy(data_, other.data_, kNumberOfTrackedSideEffects * kPointerSize);
-  }
-  return *this;
-}
-
-void HSideEffectMap::Kill(GVNFlagSet flags) {
-  for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
-    GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
-    if (flags.Contains(changes_flag)) {
-      if (data_[i] != NULL) count_--;
-      data_[i] = NULL;
-    }
-  }
-}
-
-
-void HSideEffectMap::Store(GVNFlagSet flags, HInstruction* instr) {
-  for (int i = 0; i < kNumberOfTrackedSideEffects; i++) {
-    GVNFlag changes_flag = HValue::ChangesFlagFromInt(i);
-    if (flags.Contains(changes_flag)) {
-      if (data_[i] == NULL) count_++;
-      data_[i] = instr;
-    }
-  }
-}
-
-
 class HStackCheckEliminator BASE_EMBEDDED {
  public:
   explicit HStackCheckEliminator(HGraph* graph) : graph_(graph) { }
@@ -3045,581 +2801,6 @@ void HStackCheckEliminator::Process() {
 }
 
 
-// Simple sparse set with O(1) add, contains, and clear.
-class SparseSet {
- public:
-  SparseSet(Zone* zone, int capacity)
-      : capacity_(capacity),
-        length_(0),
-        dense_(zone->NewArray<int>(capacity)),
-        sparse_(zone->NewArray<int>(capacity)) {
-#ifndef NVALGRIND
-    // Initialize the sparse array to make valgrind happy.
-    memset(sparse_, 0, sizeof(sparse_[0]) * capacity);
-#endif
-  }
-
-  bool Contains(int n) const {
-    ASSERT(0 <= n && n < capacity_);
-    int d = sparse_[n];
-    return 0 <= d && d < length_ && dense_[d] == n;
-  }
-
-  bool Add(int n) {
-    if (Contains(n)) return false;
-    dense_[length_] = n;
-    sparse_[n] = length_;
-    ++length_;
-    return true;
-  }
-
-  void Clear() { length_ = 0; }
-
- private:
-  int capacity_;
-  int length_;
-  int* dense_;
-  int* sparse_;
-
-  DISALLOW_COPY_AND_ASSIGN(SparseSet);
-};
-
-
-class HGlobalValueNumberer BASE_EMBEDDED {
- public:
-  explicit HGlobalValueNumberer(HGraph* graph, CompilationInfo* info)
-      : graph_(graph),
-        info_(info),
-        removed_side_effects_(false),
-        block_side_effects_(graph->blocks()->length(), graph->zone()),
-        loop_side_effects_(graph->blocks()->length(), graph->zone()),
-        visited_on_paths_(graph->zone(), graph->blocks()->length()) {
-#ifdef DEBUG
-    ASSERT(info->isolate()->optimizing_compiler_thread()->IsOptimizerThread() ||
-           !info->isolate()->heap()->IsAllocationAllowed());
-#endif
-    block_side_effects_.AddBlock(GVNFlagSet(), graph_->blocks()->length(),
-                                 graph_->zone());
-    loop_side_effects_.AddBlock(GVNFlagSet(), graph_->blocks()->length(),
-                                graph_->zone());
-  }
-
-  // Returns true if values with side effects are removed.
-  bool Analyze();
-
- private:
-  GVNFlagSet CollectSideEffectsOnPathsToDominatedBlock(
-      HBasicBlock* dominator,
-      HBasicBlock* dominated);
-  void AnalyzeGraph();
-  void ComputeBlockSideEffects();
-  void LoopInvariantCodeMotion();
-  void ProcessLoopBlock(HBasicBlock* block,
-                        HBasicBlock* before_loop,
-                        GVNFlagSet loop_kills,
-                        GVNFlagSet* accumulated_first_time_depends,
-                        GVNFlagSet* accumulated_first_time_changes);
-  bool AllowCodeMotion();
-  bool ShouldMove(HInstruction* instr, HBasicBlock* loop_header);
-
-  HGraph* graph() { return graph_; }
-  CompilationInfo* info() { return info_; }
-  Zone* zone() const { return graph_->zone(); }
-
-  HGraph* graph_;
-  CompilationInfo* info_;
-  bool removed_side_effects_;
-
-  // A map of block IDs to their side effects.
-  ZoneList<GVNFlagSet> block_side_effects_;
-
-  // A map of loop header block IDs to their loop's side effects.
-  ZoneList<GVNFlagSet> loop_side_effects_;
-
-  // Used when collecting side effects on paths from dominator to
-  // dominated.
-  SparseSet visited_on_paths_;
-};
-
-
-bool HGlobalValueNumberer::Analyze() {
-  removed_side_effects_ = false;
-  ComputeBlockSideEffects();
-  if (FLAG_loop_invariant_code_motion) {
-    LoopInvariantCodeMotion();
-  }
-  AnalyzeGraph();
-  return removed_side_effects_;
-}
-
-
-void HGlobalValueNumberer::ComputeBlockSideEffects() {
-  // The Analyze phase of GVN can be called multiple times. Clear loop side
-  // effects before computing them to erase the contents from previous Analyze
-  // passes.
-  for (int i = 0; i < loop_side_effects_.length(); ++i) {
-    loop_side_effects_[i].RemoveAll();
-  }
-  for (int i = graph_->blocks()->length() - 1; i >= 0; --i) {
-    // Compute side effects for the block.
-    HBasicBlock* block = graph_->blocks()->at(i);
-    HInstruction* instr = block->first();
-    int id = block->block_id();
-    GVNFlagSet side_effects;
-    while (instr != NULL) {
-      side_effects.Add(instr->ChangesFlags());
-      if (instr->IsSoftDeoptimize()) {
-        block_side_effects_[id].RemoveAll();
-        side_effects.RemoveAll();
-        break;
-      }
-      instr = instr->next();
-    }
-    block_side_effects_[id].Add(side_effects);
-
-    // Loop headers are part of their loop.
-    if (block->IsLoopHeader()) {
-      loop_side_effects_[id].Add(side_effects);
-    }
-
-    // Propagate loop side effects upwards.
-    if (block->HasParentLoopHeader()) {
-      int header_id = block->parent_loop_header()->block_id();
-      loop_side_effects_[header_id].Add(block->IsLoopHeader()
-                                        ? loop_side_effects_[id]
-                                        : side_effects);
-    }
-  }
-}
-
-
-SmartArrayPointer<char> GetGVNFlagsString(GVNFlagSet flags) {
-  char underlying_buffer[kLastFlag * 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 < kLastFlag; ++bit) {
-    if ((flags.ToIntegral() & (1 << bit)) != 0) {
-      if (bit % 2 == 0) {
-        set_changes++;
-      } else {
-        set_depends_on++;
-      }
-    }
-  }
-  bool positive_changes = set_changes < (kLastFlag / 2);
-  bool positive_depends_on = set_depends_on < (kLastFlag / 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 < kLastFlag; ++bit) {
-      if (((flags.ToIntegral() & (1 << bit)) != 0) == 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 < kLastFlag; ++bit) {
-      if (((flags.ToIntegral() & (1 << bit)) != 0) == 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 HGlobalValueNumberer::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));
-
-      GVNFlagSet accumulated_first_time_depends;
-      GVNFlagSet accumulated_first_time_changes;
-      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,
-                         &accumulated_first_time_depends,
-                         &accumulated_first_time_changes);
-      }
-    }
-  }
-}
-
-
-void HGlobalValueNumberer::ProcessLoopBlock(
-    HBasicBlock* block,
-    HBasicBlock* loop_header,
-    GVNFlagSet loop_kills,
-    GVNFlagSet* first_time_depends,
-    GVNFlagSet* first_time_changes) {
-  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));
-  HInstruction* instr = block->first();
-  while (instr != NULL) {
-    HInstruction* next = instr->next();
-    bool hoisted = false;
-    if (instr->CheckFlag(HValue::kUseGVN)) {
-      TRACE_GVN_4("Checking instruction %d (%s) %s. Loop %s\n",
-                  instr->id(),
-                  instr->Mnemonic(),
-                  *GetGVNFlagsString(instr->gvn_flags()),
-                  *GetGVNFlagsString(loop_kills));
-      bool can_hoist = !instr->gvn_flags().ContainsAnyOf(depends_flags);
-      if (can_hoist && !graph()->use_optimistic_licm()) {
-        can_hoist = block->IsLoopSuccessorDominator();
-      }
-
-      if (can_hoist) {
-        bool inputs_loop_invariant = true;
-        for (int i = 0; i < instr->OperandCount(); ++i) {
-          if (instr->OperandAt(i)->IsDefinedAfter(pre_header)) {
-            inputs_loop_invariant = false;
-          }
-        }
-
-        if (inputs_loop_invariant && ShouldMove(instr, loop_header)) {
-          TRACE_GVN_1("Hoisting loop invariant instruction %d\n", instr->id());
-          // Move the instruction out of the loop.
-          instr->Unlink();
-          instr->InsertBefore(pre_header->end());
-          if (instr->HasSideEffects()) removed_side_effects_ = true;
-          hoisted = true;
-        }
-      }
-    }
-    if (!hoisted) {
-      // If an instruction is not hoisted, we have to account for its side
-      // effects when hoisting later HTransitionElementsKind instructions.
-      GVNFlagSet previous_depends = *first_time_depends;
-      GVNFlagSet previous_changes = *first_time_changes;
-      first_time_depends->Add(instr->DependsOnFlags());
-      first_time_changes->Add(instr->ChangesFlags());
-      if (!(previous_depends == *first_time_depends)) {
-        TRACE_GVN_1("Updated first-time accumulated %s\n",
-                    *GetGVNFlagsString(*first_time_depends));
-      }
-      if (!(previous_changes == *first_time_changes)) {
-        TRACE_GVN_1("Updated first-time accumulated %s\n",
-                    *GetGVNFlagsString(*first_time_changes));
-      }
-    }
-    instr = next;
-  }
-}
-
-
-bool HGlobalValueNumberer::AllowCodeMotion() {
-  return info()->IsStub() || info()->opt_count() + 1 < FLAG_max_opt_count;
-}
-
-
-bool HGlobalValueNumberer::ShouldMove(HInstruction* instr,
-                                      HBasicBlock* loop_header) {
-  // If we've disabled code motion or we're in a block that unconditionally
-  // deoptimizes, don't move any instructions.
-  return AllowCodeMotion() && !instr->block()->IsDeoptimizing();
-}
-
-
-GVNFlagSet HGlobalValueNumberer::CollectSideEffectsOnPathsToDominatedBlock(
-    HBasicBlock* dominator, HBasicBlock* dominated) {
-  GVNFlagSet side_effects;
-  for (int i = 0; i < dominated->predecessors()->length(); ++i) {
-    HBasicBlock* block = dominated->predecessors()->at(i);
-    if (dominator->block_id() < block->block_id() &&
-        block->block_id() < dominated->block_id() &&
-        visited_on_paths_.Add(block->block_id())) {
-      side_effects.Add(block_side_effects_[block->block_id()]);
-      if (block->IsLoopHeader()) {
-        side_effects.Add(loop_side_effects_[block->block_id()]);
-      }
-      side_effects.Add(CollectSideEffectsOnPathsToDominatedBlock(
-          dominator, block));
-    }
-  }
-  return side_effects;
-}
-
-
-// Each instance of this class is like a "stack frame" for the recursive
-// traversal of the dominator tree done during GVN (the stack is handled
-// as a double linked list).
-// We reuse frames when possible so the list length is limited by the depth
-// of the dominator tree but this forces us to initialize each frame calling
-// an explicit "Initialize" method instead of a using constructor.
-class GvnBasicBlockState: public ZoneObject {
- public:
-  static GvnBasicBlockState* CreateEntry(Zone* zone,
-                                         HBasicBlock* entry_block,
-                                         HValueMap* entry_map) {
-    return new(zone)
-        GvnBasicBlockState(NULL, entry_block, entry_map, NULL, zone);
-  }
-
-  HBasicBlock* block() { return block_; }
-  HValueMap* map() { return map_; }
-  HSideEffectMap* dominators() { return &dominators_; }
-
-  GvnBasicBlockState* next_in_dominator_tree_traversal(
-      Zone* zone,
-      HBasicBlock** dominator) {
-    // This assignment needs to happen before calling next_dominated() because
-    // that call can reuse "this" if we are at the last dominated block.
-    *dominator = block();
-    GvnBasicBlockState* result = next_dominated(zone);
-    if (result == NULL) {
-      GvnBasicBlockState* dominator_state = pop();
-      if (dominator_state != NULL) {
-        // This branch is guaranteed not to return NULL because pop() never
-        // returns a state where "is_done() == true".
-        *dominator = dominator_state->block();
-        result = dominator_state->next_dominated(zone);
-      } else {
-        // Unnecessary (we are returning NULL) but done for cleanness.
-        *dominator = NULL;
-      }
-    }
-    return result;
-  }
-
- private:
-  void Initialize(HBasicBlock* block,
-                  HValueMap* map,
-                  HSideEffectMap* dominators,
-                  bool copy_map,
-                  Zone* zone) {
-    block_ = block;
-    map_ = copy_map ? map->Copy(zone) : map;
-    dominated_index_ = -1;
-    length_ = block->dominated_blocks()->length();
-    if (dominators != NULL) {
-      dominators_ = *dominators;
-    }
-  }
-  bool is_done() { return dominated_index_ >= length_; }
-
-  GvnBasicBlockState(GvnBasicBlockState* previous,
-                     HBasicBlock* block,
-                     HValueMap* map,
-                     HSideEffectMap* dominators,
-                     Zone* zone)
-      : previous_(previous), next_(NULL) {
-    Initialize(block, map, dominators, true, zone);
-  }
-
-  GvnBasicBlockState* next_dominated(Zone* zone) {
-    dominated_index_++;
-    if (dominated_index_ == length_ - 1) {
-      // No need to copy the map for the last child in the dominator tree.
-      Initialize(block_->dominated_blocks()->at(dominated_index_),
-                 map(),
-                 dominators(),
-                 false,
-                 zone);
-      return this;
-    } else if (dominated_index_ < length_) {
-      return push(zone,
-                  block_->dominated_blocks()->at(dominated_index_),
-                  dominators());
-    } else {
-      return NULL;
-    }
-  }
-
-  GvnBasicBlockState* push(Zone* zone,
-                           HBasicBlock* block,
-                           HSideEffectMap* dominators) {
-    if (next_ == NULL) {
-      next_ =
-          new(zone) GvnBasicBlockState(this, block, map(), dominators, zone);
-    } else {
-      next_->Initialize(block, map(), dominators, true, zone);
-    }
-    return next_;
-  }
-  GvnBasicBlockState* pop() {
-    GvnBasicBlockState* result = previous_;
-    while (result != NULL && result->is_done()) {
-      TRACE_GVN_2("Backtracking from block B%d to block b%d\n",
-                  block()->block_id(),
-                  previous_->block()->block_id())
-      result = result->previous_;
-    }
-    return result;
-  }
-
-  GvnBasicBlockState* previous_;
-  GvnBasicBlockState* next_;
-  HBasicBlock* block_;
-  HValueMap* map_;
-  HSideEffectMap dominators_;
-  int dominated_index_;
-  int length_;
-};
-
-// This is a recursive traversal of the dominator tree but it has been turned
-// into a loop to avoid stack overflows.
-// The logical "stack frames" of the recursion are kept in a list of
-// GvnBasicBlockState instances.
-void HGlobalValueNumberer::AnalyzeGraph() {
-  HBasicBlock* entry_block = graph_->entry_block();
-  HValueMap* entry_map = new(zone()) HValueMap(zone());
-  GvnBasicBlockState* current =
-      GvnBasicBlockState::CreateEntry(zone(), entry_block, entry_map);
-
-  while (current != NULL) {
-    HBasicBlock* block = current->block();
-    HValueMap* map = current->map();
-    HSideEffectMap* dominators = current->dominators();
-
-    TRACE_GVN_2("Analyzing block B%d%s\n",
-                block->block_id(),
-                block->IsLoopHeader() ? " (loop header)" : "");
-
-    // If this is a loop header kill everything killed by the loop.
-    if (block->IsLoopHeader()) {
-      map->Kill(loop_side_effects_[block->block_id()]);
-    }
-
-    // Go through all instructions of the current block.
-    HInstruction* instr = block->first();
-    while (instr != NULL) {
-      HInstruction* next = instr->next();
-      GVNFlagSet flags = instr->ChangesFlags();
-      if (!flags.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));
-      }
-      if (instr->CheckFlag(HValue::kUseGVN)) {
-        ASSERT(!instr->HasObservableSideEffects());
-        HValue* 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",
-                      instr->id(),
-                      instr->Mnemonic(),
-                      other->id(),
-                      other->Mnemonic());
-          if (instr->HasSideEffects()) removed_side_effects_ = true;
-          instr->DeleteAndReplaceWith(other);
-        } else {
-          map->Add(instr, zone());
-        }
-      }
-      if (instr->IsLinked() &&
-          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)) {
-            TRACE_GVN_5("Side-effect #%d in %d (%s) is dominated by %d (%s)\n",
-                        i,
-                        instr->id(),
-                        instr->Mnemonic(),
-                        other->id(),
-                        other->Mnemonic());
-            instr->SetSideEffectDominator(changes_flag, other);
-          }
-        }
-      }
-      instr = next;
-    }
-
-    HBasicBlock* dominator_block;
-    GvnBasicBlockState* next =
-        current->next_in_dominator_tree_traversal(zone(), &dominator_block);
-
-    if (next != NULL) {
-      HBasicBlock* dominated = next->block();
-      HValueMap* successor_map = next->map();
-      HSideEffectMap* successor_dominators = next->dominators();
-
-      // Kill everything killed on any path between this block and the
-      // dominated block.  We don't have to traverse these paths if the
-      // value map and the dominators list is already empty.  If the range
-      // of block ids (block_id, dominated_id) is empty there are no such
-      // paths.
-      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 =
-            CollectSideEffectsOnPathsToDominatedBlock(dominator_block,
-                                                      dominated);
-        successor_map->Kill(side_effects_on_all_paths);
-        successor_dominators->Kill(side_effects_on_all_paths);
-      }
-    }
-    current = next;
-  }
-}
-
-
 void HInferRepresentation::AddToWorklist(HValue* current) {
   if (current->representation().IsTagged()) return;
   if (!current->CheckFlag(HValue::kFlexibleRepresentation)) return;