Move ConstantPropagator from flow_graph_optimizer.cc/.h into separate files.

runtime/vm/flow_graph_optimizer.cc

Index: runtime/vm/flow_graph_optimizer.cc
===================================================================
--- runtime/vm/flow_graph_optimizer.cc	(revision 42566)
+++ runtime/vm/flow_graph_optimizer.cc	(working copy)
@@ -33,9 +33,6 @@
 DEFINE_FLAG(int, max_equality_polymorphic_checks, 32,
     "Maximum number of polymorphic checks in equality operator,"
     " otherwise use megamorphic dispatch.");
-DEFINE_FLAG(bool, remove_redundant_phis, true, "Remove redundant phis.");
-DEFINE_FLAG(bool, trace_constant_propagation, false,
-    "Print constant propagation and useless code elimination.");
 DEFINE_FLAG(bool, trace_load_optimization, false,
     "Print live sets for load optimization pass.");
 DEFINE_FLAG(bool, trace_optimization, false, "Print optimization details.");
@@ -7500,1619 +7497,6 @@
 }
 
 
-ConstantPropagator::ConstantPropagator(
-    FlowGraph* graph,
-    const GrowableArray<BlockEntryInstr*>& ignored)
-    : FlowGraphVisitor(ignored),
-      graph_(graph),
-      unknown_(Object::unknown_constant()),
-      non_constant_(Object::non_constant()),
-      reachable_(new(graph->isolate()) BitVector(
-          graph->isolate(), graph->preorder().length())),
-      marked_phis_(new(graph->isolate()) BitVector(
-          graph->isolate(), graph->max_virtual_register_number())),
-      block_worklist_(),
-      definition_worklist_(graph, 10) {}
-
-
-void ConstantPropagator::Optimize(FlowGraph* graph) {
-  GrowableArray<BlockEntryInstr*> ignored;
-  ConstantPropagator cp(graph, ignored);
-  cp.Analyze();
-  cp.Transform();
-}
-
-
-void ConstantPropagator::OptimizeBranches(FlowGraph* graph) {
-  GrowableArray<BlockEntryInstr*> ignored;
-  ConstantPropagator cp(graph, ignored);
-  cp.Analyze();
-  cp.Transform();
-  cp.EliminateRedundantBranches();
-}
-
-
-void ConstantPropagator::SetReachable(BlockEntryInstr* block) {
-  if (!reachable_->Contains(block->preorder_number())) {
-    reachable_->Add(block->preorder_number());
-    block_worklist_.Add(block);
-  }
-}
-
-
-bool ConstantPropagator::SetValue(Definition* definition, const Object& value) {
-  // We would like to assert we only go up (toward non-constant) in the lattice.
-  //
-  // ASSERT(IsUnknown(definition->constant_value()) ||
-  //        IsNonConstant(value) ||
-  //        (definition->constant_value().raw() == value.raw()));
-  //
-  // But the final disjunct is not true (e.g., mint or double constants are
-  // heap-allocated and so not necessarily pointer-equal on each iteration).
-  if (definition->constant_value().raw() != value.raw()) {
-    definition->constant_value() = value.raw();
-    if (definition->input_use_list() != NULL) {
-      definition_worklist_.Add(definition);
-    }
-    return true;
-  }
-  return false;
-}
-
-
-// Compute the join of two values in the lattice, assign it to the first.
-void ConstantPropagator::Join(Object* left, const Object& right) {
-  // Join(non-constant, X) = non-constant
-  // Join(X, unknown)      = X
-  if (IsNonConstant(*left) || IsUnknown(right)) return;
-
-  // Join(unknown, X)      = X
-  // Join(X, non-constant) = non-constant
-  if (IsUnknown(*left) || IsNonConstant(right)) {
-    *left = right.raw();
-    return;
-  }
-
-  // Join(X, X) = X
-  // TODO(kmillikin): support equality for doubles, mints, etc.
-  if (left->raw() == right.raw()) return;
-
-  // Join(X, Y) = non-constant
-  *left = non_constant_.raw();
-}
-
-
-// --------------------------------------------------------------------------
-// Analysis of blocks.  Called at most once per block.  The block is already
-// marked as reachable.  All instructions in the block are analyzed.
-void ConstantPropagator::VisitGraphEntry(GraphEntryInstr* block) {
-  const GrowableArray<Definition*>& defs = *block->initial_definitions();
-  for (intptr_t i = 0; i < defs.length(); ++i) {
-    defs[i]->Accept(this);
-  }
-  ASSERT(ForwardInstructionIterator(block).Done());
-
-  // TODO(fschneider): Improve this approximation. The catch entry is only
-  // reachable if a call in the try-block is reachable.
-  for (intptr_t i = 0; i < block->SuccessorCount(); ++i) {
-    SetReachable(block->SuccessorAt(i));
-  }
-}
-
-
-void ConstantPropagator::VisitJoinEntry(JoinEntryInstr* block) {
-  // Phis are visited when visiting Goto at a predecessor. See VisitGoto.
-  for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
-    it.Current()->Accept(this);
-  }
-}
-
-
-void ConstantPropagator::VisitTargetEntry(TargetEntryInstr* block) {
-  for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
-    it.Current()->Accept(this);
-  }
-}
-
-
-void ConstantPropagator::VisitIndirectEntry(IndirectEntryInstr* block) {
-  for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
-    it.Current()->Accept(this);
-  }
-}
-
-
-void ConstantPropagator::VisitCatchBlockEntry(CatchBlockEntryInstr* block) {
-  const GrowableArray<Definition*>& defs = *block->initial_definitions();
-  for (intptr_t i = 0; i < defs.length(); ++i) {
-    defs[i]->Accept(this);
-  }
-  for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
-    it.Current()->Accept(this);
-  }
-}
-
-
-void ConstantPropagator::VisitParallelMove(ParallelMoveInstr* instr) {
-  // Parallel moves have not yet been inserted in the graph.
-  UNREACHABLE();
-}
-
-
-// --------------------------------------------------------------------------
-// Analysis of control instructions.  Unconditional successors are
-// reachable.  Conditional successors are reachable depending on the
-// constant value of the condition.
-void ConstantPropagator::VisitReturn(ReturnInstr* instr) {
-  // Nothing to do.
-}
-
-
-void ConstantPropagator::VisitThrow(ThrowInstr* instr) {
-  // Nothing to do.
-}
-
-
-void ConstantPropagator::VisitReThrow(ReThrowInstr* instr) {
-  // Nothing to do.
-}
-
-
-void ConstantPropagator::VisitGoto(GotoInstr* instr) {
-  SetReachable(instr->successor());
-
-  // Phi value depends on the reachability of a predecessor. We have
-  // to revisit phis every time a predecessor becomes reachable.
-  for (PhiIterator it(instr->successor()); !it.Done(); it.Advance()) {
-    it.Current()->Accept(this);
-  }
-}
-
-
-void ConstantPropagator::VisitIndirectGoto(IndirectGotoInstr* instr) {
-  for (intptr_t i = 0; i < instr->SuccessorCount(); i++) {
-    SetReachable(instr->SuccessorAt(i));
-  }
-}
-
-
-void ConstantPropagator::VisitBranch(BranchInstr* instr) {
-  instr->comparison()->Accept(this);
-
-  // The successors may be reachable, but only if this instruction is.  (We
-  // might be analyzing it because the constant value of one of its inputs
-  // has changed.)
-  if (reachable_->Contains(instr->GetBlock()->preorder_number())) {
-    if (instr->constant_target() != NULL) {
-      ASSERT((instr->constant_target() == instr->true_successor()) ||
-             (instr->constant_target() == instr->false_successor()));
-      SetReachable(instr->constant_target());
-    } else {
-      const Object& value = instr->comparison()->constant_value();
-      if (IsNonConstant(value)) {
-        SetReachable(instr->true_successor());
-        SetReachable(instr->false_successor());
-      } else if (value.raw() == Bool::True().raw()) {
-        SetReachable(instr->true_successor());
-      } else if (!IsUnknown(value)) {  // Any other constant.
-        SetReachable(instr->false_successor());
-      }
-    }
-  }
-}
-
-
-// --------------------------------------------------------------------------
-// Analysis of non-definition instructions.  They do not have values so they
-// cannot have constant values.
-void ConstantPropagator::VisitCheckStackOverflow(
-    CheckStackOverflowInstr* instr) { }
-
-
-void ConstantPropagator::VisitCheckClass(CheckClassInstr* instr) { }
-
-
-void ConstantPropagator::VisitCheckClassId(CheckClassIdInstr* instr) { }
-
-
-void ConstantPropagator::VisitGuardFieldClass(GuardFieldClassInstr* instr) { }
-
-
-void ConstantPropagator::VisitGuardFieldLength(GuardFieldLengthInstr* instr) { }
-
-
-void ConstantPropagator::VisitCheckSmi(CheckSmiInstr* instr) { }
-
-
-void ConstantPropagator::VisitCheckEitherNonSmi(
-    CheckEitherNonSmiInstr* instr) { }
-
-
-void ConstantPropagator::VisitCheckArrayBound(CheckArrayBoundInstr* instr) { }
-
-
-void ConstantPropagator::VisitDeoptimize(DeoptimizeInstr* instr) {
-  // TODO(vegorov) remove all code after DeoptimizeInstr as dead.
-}
-
-
-Definition* ConstantPropagator::UnwrapPhi(Definition* defn) {
-  if (defn->IsPhi()) {
-    JoinEntryInstr* block = defn->AsPhi()->block();
-
-    Definition* input = NULL;
-    for (intptr_t i = 0; i < defn->InputCount(); ++i) {
-      if (reachable_->Contains(block->PredecessorAt(i)->preorder_number())) {
-        if (input == NULL) {
-          input = defn->InputAt(i)->definition();
-        } else {
-          return defn;
-        }
-      }
-    }
-
-    return input;
-  }
-
-  return defn;
-}
-
-
-void ConstantPropagator::MarkPhi(Definition* phi) {
-  ASSERT(phi->IsPhi());
-  marked_phis_->Add(phi->ssa_temp_index());
-}
-
-
-// --------------------------------------------------------------------------
-// Analysis of definitions.  Compute the constant value.  If it has changed
-// and the definition has input uses, add the definition to the definition
-// worklist so that the used can be processed.
-void ConstantPropagator::VisitPhi(PhiInstr* instr) {
-  // Compute the join over all the reachable predecessor values.
-  JoinEntryInstr* block = instr->block();
-  Object& value = Object::ZoneHandle(I, Unknown());
-  for (intptr_t pred_idx = 0; pred_idx < instr->InputCount(); ++pred_idx) {
-    if (reachable_->Contains(
-            block->PredecessorAt(pred_idx)->preorder_number())) {
-      Join(&value,
-           instr->InputAt(pred_idx)->definition()->constant_value());
-    }
-  }
-  if (!SetValue(instr, value) &&
-      marked_phis_->Contains(instr->ssa_temp_index())) {
-    marked_phis_->Remove(instr->ssa_temp_index());
-    definition_worklist_.Add(instr);
-  }
-}
-
-
-void ConstantPropagator::VisitRedefinition(RedefinitionInstr* instr) {
-  SetValue(instr, instr->value()->definition()->constant_value());
-}
-
-
-void ConstantPropagator::VisitParameter(ParameterInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitPushArgument(PushArgumentInstr* instr) {
-  SetValue(instr, instr->value()->definition()->constant_value());
-}
-
-
-void ConstantPropagator::VisitAssertAssignable(AssertAssignableInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    // We are ignoring the instantiator and instantiator_type_arguments, but
-    // still monotonic and safe.
-    if (instr->value()->Type()->IsAssignableTo(instr->dst_type())) {
-      SetValue(instr, value);
-    } else {
-      SetValue(instr, non_constant_);
-    }
-  }
-}
-
-
-void ConstantPropagator::VisitAssertBoolean(AssertBooleanInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    if (value.IsBool()) {
-      SetValue(instr, value);
-    } else {
-      SetValue(instr, non_constant_);
-    }
-  }
-}
-
-
-void ConstantPropagator::VisitCurrentContext(CurrentContextInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitClosureCall(ClosureCallInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInstanceCall(InstanceCallInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitPolymorphicInstanceCall(
-    PolymorphicInstanceCallInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitStaticCall(StaticCallInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitLoadLocal(LoadLocalInstr* instr) {
-  // Instruction is eliminated when translating to SSA.
-  UNREACHABLE();
-}
-
-
-void ConstantPropagator::VisitPushTemp(PushTempInstr* instr) {
-  // Instruction is eliminated when translating to SSA.
-  UNREACHABLE();
-}
-
-
-void ConstantPropagator::VisitDropTemps(DropTempsInstr* instr) {
-  // Instruction is eliminated when translating to SSA.
-  UNREACHABLE();
-}
-
-
-void ConstantPropagator::VisitStoreLocal(StoreLocalInstr* instr) {
-  // Instruction is eliminated when translating to SSA.
-  UNREACHABLE();
-}
-
-
-void ConstantPropagator::VisitIfThenElse(IfThenElseInstr* instr) {
-  instr->comparison()->Accept(this);
-  const Object& value = instr->comparison()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    ASSERT(!value.IsNull());
-    ASSERT(value.IsBool());
-    bool result = Bool::Cast(value).value();
-    SetValue(instr,
-             Smi::Handle(I, Smi::New(
-                 result ? instr->if_true() : instr->if_false())));
-  }
-}
-
-
-void ConstantPropagator::VisitStrictCompare(StrictCompareInstr* instr) {
-  Definition* left_defn = instr->left()->definition();
-  Definition* right_defn = instr->right()->definition();
-
-  Definition* unwrapped_left_defn = UnwrapPhi(left_defn);
-  Definition* unwrapped_right_defn = UnwrapPhi(right_defn);
-  if (unwrapped_left_defn == unwrapped_right_defn) {
-    // Fold x === x, and x !== x to true/false.
-    SetValue(instr, Bool::Get(instr->kind() == Token::kEQ_STRICT));
-    if (unwrapped_left_defn != left_defn) {
-      MarkPhi(left_defn);
-    }
-    if (unwrapped_right_defn != right_defn) {
-      MarkPhi(right_defn);
-    }
-    return;
-  }
-
-  const Object& left = left_defn->constant_value();
-  const Object& right = right_defn->constant_value();
-  if (IsNonConstant(left) || IsNonConstant(right)) {
-    // TODO(vegorov): incorporate nullability information into the lattice.
-    if ((left.IsNull() && instr->right()->Type()->HasDecidableNullability()) ||
-        (right.IsNull() && instr->left()->Type()->HasDecidableNullability())) {
-      bool result = left.IsNull() ? instr->right()->Type()->IsNull()
-                                  : instr->left()->Type()->IsNull();
-      if (instr->kind() == Token::kNE_STRICT) {
-        result = !result;
-      }
-      SetValue(instr, Bool::Get(result));
-    } else {
-      const intptr_t left_cid = instr->left()->Type()->ToCid();
-      const intptr_t right_cid = instr->right()->Type()->ToCid();
-      // If exact classes (cids) are known and they differ, the result
-      // of strict compare can be computed.
-      if ((left_cid != kDynamicCid) && (right_cid != kDynamicCid) &&
-          (left_cid != right_cid)) {
-        const bool result = (instr->kind() != Token::kEQ_STRICT);
-        SetValue(instr, Bool::Get(result));
-      } else {
-        SetValue(instr, non_constant_);
-      }
-    }
-  } else if (IsConstant(left) && IsConstant(right)) {
-    bool result = (left.raw() == right.raw());
-    if (instr->kind() == Token::kNE_STRICT) {
-      result = !result;
-    }
-    SetValue(instr, Bool::Get(result));
-  }
-}
-
-
-static bool CompareIntegers(Token::Kind kind,
-                            const Integer& left,
-                            const Integer& right) {
-  const int result = left.CompareWith(right);
-  switch (kind) {
-    case Token::kEQ: return (result == 0);
-    case Token::kNE: return (result != 0);
-    case Token::kLT: return (result < 0);
-    case Token::kGT: return (result > 0);
-    case Token::kLTE: return (result <= 0);
-    case Token::kGTE: return (result >= 0);
-    default:
-      UNREACHABLE();
-      return false;
-  }
-}
-
-
-void ConstantPropagator::VisitTestSmi(TestSmiInstr* instr) {
-  const Object& left = instr->left()->definition()->constant_value();
-  const Object& right = instr->right()->definition()->constant_value();
-  if (IsNonConstant(left) || IsNonConstant(right)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(left) && IsConstant(right)) {
-    if (left.IsInteger() && right.IsInteger()) {
-      const bool result = CompareIntegers(
-          instr->kind(),
-          Integer::Handle(I, Integer::Cast(left).BitOp(Token::kBIT_AND,
-                                                       Integer::Cast(right))),
-          Smi::Handle(I, Smi::New(0)));
-      SetValue(instr, result ? Bool::True() : Bool::False());
-    } else {
-      SetValue(instr, non_constant_);
-    }
-  }
-}
-
-
-void ConstantPropagator::VisitTestCids(TestCidsInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitEqualityCompare(EqualityCompareInstr* instr) {
-  Definition* left_defn = instr->left()->definition();
-  Definition* right_defn = instr->right()->definition();
-
-  if (RawObject::IsIntegerClassId(instr->operation_cid())) {
-    // Fold x == x, and x != x to true/false for numbers comparisons.
-    Definition* unwrapped_left_defn = UnwrapPhi(left_defn);
-    Definition* unwrapped_right_defn = UnwrapPhi(right_defn);
-    if (unwrapped_left_defn == unwrapped_right_defn) {
-      // Fold x === x, and x !== x to true/false.
-      SetValue(instr, Bool::Get(instr->kind() == Token::kEQ));
-      if (unwrapped_left_defn != left_defn) {
-        MarkPhi(left_defn);
-      }
-      if (unwrapped_right_defn != right_defn) {
-        MarkPhi(right_defn);
-      }
-      return;
-    }
-  }
-
-  const Object& left = left_defn->constant_value();
-  const Object& right = right_defn->constant_value();
-  if (IsNonConstant(left) || IsNonConstant(right)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(left) && IsConstant(right)) {
-    if (left.IsInteger() && right.IsInteger()) {
-      const bool result = CompareIntegers(instr->kind(),
-                                          Integer::Cast(left),
-                                          Integer::Cast(right));
-      SetValue(instr, Bool::Get(result));
-    } else if (left.IsString() && right.IsString()) {
-      const bool result = String::Cast(left).Equals(String::Cast(right));
-      SetValue(instr, Bool::Get((instr->kind() == Token::kEQ) == result));
-    } else {
-      SetValue(instr, non_constant_);
-    }
-  }
-}
-
-
-void ConstantPropagator::VisitRelationalOp(RelationalOpInstr* instr) {
-  const Object& left = instr->left()->definition()->constant_value();
-  const Object& right = instr->right()->definition()->constant_value();
-  if (IsNonConstant(left) || IsNonConstant(right)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(left) && IsConstant(right)) {
-    if (left.IsInteger() && right.IsInteger()) {
-      const bool result = CompareIntegers(instr->kind(),
-                                          Integer::Cast(left),
-                                          Integer::Cast(right));
-      SetValue(instr, Bool::Get(result));
-    } else if (left.IsDouble() && right.IsDouble()) {
-      // TODO(srdjan): Implement.
-      SetValue(instr, non_constant_);
-    } else {
-      SetValue(instr, non_constant_);
-    }
-  }
-}
-
-
-void ConstantPropagator::VisitNativeCall(NativeCallInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitDebugStepCheck(DebugStepCheckInstr* instr) {
-  // Nothing to do.
-}
-
-
-void ConstantPropagator::VisitStringFromCharCode(
-    StringFromCharCodeInstr* instr) {
-  const Object& o = instr->char_code()->definition()->constant_value();
-  if (o.IsNull() || IsNonConstant(o)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(o)) {
-    const intptr_t ch_code = Smi::Cast(o).Value();
-    ASSERT(ch_code >= 0);
-    if (ch_code < Symbols::kMaxOneCharCodeSymbol) {
-      RawString** table = Symbols::PredefinedAddress();
-      SetValue(instr, String::ZoneHandle(I, table[ch_code]));
-    } else {
-      SetValue(instr, non_constant_);
-    }
-  }
-}
-
-
-void ConstantPropagator::VisitStringToCharCode(StringToCharCodeInstr* instr) {
-  const Object& o = instr->str()->definition()->constant_value();
-  if (o.IsNull() || IsNonConstant(o)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(o)) {
-    const String& str = String::Cast(o);
-    const intptr_t result =
-        (str.Length() == 1) ? static_cast<intptr_t>(str.CharAt(0)) : -1;
-    SetValue(instr, Smi::ZoneHandle(I, Smi::New(result)));
-  }
-}
-
-
-void ConstantPropagator::VisitStringInterpolate(StringInterpolateInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitLoadIndexed(LoadIndexedInstr* instr) {
-  const Object& array_obj = instr->array()->definition()->constant_value();
-  const Object& index_obj = instr->index()->definition()->constant_value();
-  if (IsNonConstant(array_obj) || IsNonConstant(index_obj)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(array_obj) && IsConstant(index_obj)) {
-    // Need index to be Smi and array to be either String or an immutable array.
-    if (!index_obj.IsSmi()) {
-      // Should not occur.
-      SetValue(instr, non_constant_);
-      return;
-    }
-    const intptr_t index = Smi::Cast(index_obj).Value();
-    if (index >= 0) {
-      if (array_obj.IsString()) {
-        const String& str = String::Cast(array_obj);
-        if (str.Length() > index) {
-          SetValue(instr, Smi::Handle(I,
-              Smi::New(static_cast<intptr_t>(str.CharAt(index)))));
-          return;
-        }
-      } else if (array_obj.IsArray()) {
-        const Array& a = Array::Cast(array_obj);
-        if ((a.Length() > index) && a.IsImmutable()) {
-          Instance& result = Instance::Handle(I);
-          result ^= a.At(index);
-          SetValue(instr, result);
-          return;
-        }
-      }
-    }
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitLoadCodeUnits(LoadCodeUnitsInstr* instr) {
-  // TODO(zerny): Implement constant propagation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitStoreIndexed(StoreIndexedInstr* instr) {
-  SetValue(instr, instr->value()->definition()->constant_value());
-}
-
-
-void ConstantPropagator::VisitStoreInstanceField(
-    StoreInstanceFieldInstr* instr) {
-  SetValue(instr, instr->value()->definition()->constant_value());
-}
-
-
-void ConstantPropagator::VisitInitStaticField(InitStaticFieldInstr* instr) {
-  // Nothing to do.
-}
-
-
-void ConstantPropagator::VisitLoadStaticField(LoadStaticFieldInstr* instr) {
-  const Field& field = instr->StaticField();
-  ASSERT(field.is_static());
-  if (field.is_final()) {
-    Instance& obj = Instance::Handle(I, field.value());
-    ASSERT(obj.raw() != Object::sentinel().raw());
-    ASSERT(obj.raw() != Object::transition_sentinel().raw());
-    if (obj.IsSmi() || obj.IsOld()) {
-      SetValue(instr, obj);
-      return;
-    }
-  }
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitStoreStaticField(StoreStaticFieldInstr* instr) {
-  SetValue(instr, instr->value()->definition()->constant_value());
-}
-
-
-void ConstantPropagator::VisitBooleanNegate(BooleanNegateInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    bool val = value.raw() != Bool::True().raw();
-    SetValue(instr, Bool::Get(val));
-  }
-}
-
-
-void ConstantPropagator::VisitInstanceOf(InstanceOfInstr* instr) {
-  const Definition* def = instr->value()->definition();
-  const Object& value = def->constant_value();
-  if (IsNonConstant(value)) {
-    const AbstractType& checked_type = instr->type();
-    intptr_t value_cid = instr->value()->Type()->ToCid();
-    Representation rep = def->representation();
-    if ((checked_type.IsFloat32x4Type() && (rep == kUnboxedFloat32x4)) ||
-        (checked_type.IsInt32x4Type() && (rep == kUnboxedInt32x4)) ||
-        (checked_type.IsDoubleType() && (rep == kUnboxedDouble) &&
-         CanUnboxDouble()) ||
-        (checked_type.IsIntType() && (rep == kUnboxedMint))) {
-      // Ensure that compile time type matches representation.
-      ASSERT(((rep == kUnboxedFloat32x4) && (value_cid == kFloat32x4Cid)) ||
-             ((rep == kUnboxedInt32x4) && (value_cid == kInt32x4Cid)) ||
-             ((rep == kUnboxedDouble) && (value_cid == kDoubleCid)) ||
-             ((rep == kUnboxedMint) && (value_cid == kMintCid)));
-      // The representation guarantees the type check to be true.
-      SetValue(instr, instr->negate_result() ? Bool::False() : Bool::True());
-    } else {
-      SetValue(instr, non_constant_);
-    }
-  } else if (IsConstant(value)) {
-    // TODO(kmillikin): Handle instanceof on constants.
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitCreateArray(CreateArrayInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitAllocateObject(AllocateObjectInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitLoadUntagged(LoadUntaggedInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitLoadClassId(LoadClassIdInstr* instr) {
-  intptr_t cid = instr->object()->Type()->ToCid();
-  if (cid != kDynamicCid) {
-    SetValue(instr, Smi::ZoneHandle(I, Smi::New(cid)));
-    return;
-  }
-  const Object& object = instr->object()->definition()->constant_value();
-  if (IsConstant(object)) {
-    SetValue(instr, Smi::ZoneHandle(I, Smi::New(object.GetClassId())));
-    return;
-  }
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitLoadField(LoadFieldInstr* instr) {
-  Value* instance = instr->instance();
-  if ((instr->recognized_kind() == MethodRecognizer::kObjectArrayLength) &&
-      instance->definition()->OriginalDefinition()->IsCreateArray()) {
-    Value* num_elements = instance->definition()->OriginalDefinition()
-        ->AsCreateArray()->num_elements();
-    if (num_elements->BindsToConstant() &&
-        num_elements->BoundConstant().IsSmi()) {
-      intptr_t length = Smi::Cast(num_elements->BoundConstant()).Value();
-      const Object& result = Smi::ZoneHandle(I, Smi::New(length));
-      SetValue(instr, result);
-      return;
-    }
-  }
-
-  if (instr->IsImmutableLengthLoad()) {
-    ConstantInstr* constant =
-        instance->definition()->OriginalDefinition()->AsConstant();
-    if (constant != NULL) {
-      if (constant->value().IsString()) {
-        SetValue(instr, Smi::ZoneHandle(I,
-            Smi::New(String::Cast(constant->value()).Length())));
-        return;
-      }
-      if (constant->value().IsArray()) {
-        SetValue(instr, Smi::ZoneHandle(I,
-            Smi::New(Array::Cast(constant->value()).Length())));
-        return;
-      }
-    }
-  }
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInstantiateType(InstantiateTypeInstr* instr) {
-  const Object& object =
-      instr->instantiator()->definition()->constant_value();
-  if (IsNonConstant(object)) {
-    SetValue(instr, non_constant_);
-    return;
-  }
-  if (IsConstant(object)) {
-    if (instr->type().IsTypeParameter()) {
-      if (object.IsNull()) {
-        SetValue(instr, Type::ZoneHandle(I, Type::DynamicType()));
-        return;
-      }
-      // We could try to instantiate the type parameter and return it if no
-      // malformed error is reported.
-    }
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitInstantiateTypeArguments(
-    InstantiateTypeArgumentsInstr* instr) {
-  const Object& object =
-      instr->instantiator()->definition()->constant_value();
-  if (IsNonConstant(object)) {
-    SetValue(instr, non_constant_);
-    return;
-  }
-  if (IsConstant(object)) {
-    const intptr_t len = instr->type_arguments().Length();
-    if (instr->type_arguments().IsRawInstantiatedRaw(len) &&
-        object.IsNull()) {
-      SetValue(instr, object);
-      return;
-    }
-    if (instr->type_arguments().IsUninstantiatedIdentity() ||
-        instr->type_arguments().CanShareInstantiatorTypeArguments(
-            instr->instantiator_class())) {
-      SetValue(instr, object);
-      return;
-    }
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitAllocateContext(AllocateContextInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitAllocateUninitializedContext(
-    AllocateUninitializedContextInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitCloneContext(CloneContextInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitBinaryIntegerOp(BinaryIntegerOpInstr* binary_op) {
-  const Object& left = binary_op->left()->definition()->constant_value();
-  const Object& right = binary_op->right()->definition()->constant_value();
-  if (IsConstant(left) && IsConstant(right)) {
-    if (left.IsInteger() && right.IsInteger()) {
-      const Integer& left_int = Integer::Cast(left);
-      const Integer& right_int = Integer::Cast(right);
-      const Integer& result =
-          Integer::Handle(I, binary_op->Evaluate(left_int, right_int));
-      if (!result.IsNull()) {
-        SetValue(binary_op, Integer::ZoneHandle(I, result.raw()));
-        return;
-      }
-    }
-  }
-
-  SetValue(binary_op, non_constant_);
-}
-
-
-void ConstantPropagator::VisitBinarySmiOp(BinarySmiOpInstr* instr) {
-  VisitBinaryIntegerOp(instr);
-}
-
-
-void ConstantPropagator::VisitBinaryInt32Op(BinaryInt32OpInstr* instr) {
-  VisitBinaryIntegerOp(instr);
-}
-
-
-void ConstantPropagator::VisitBinaryUint32Op(BinaryUint32OpInstr* instr) {
-  VisitBinaryIntegerOp(instr);
-}
-
-
-void ConstantPropagator::VisitShiftUint32Op(ShiftUint32OpInstr* instr) {
-  VisitBinaryIntegerOp(instr);
-}
-
-
-void ConstantPropagator::VisitBinaryMintOp(BinaryMintOpInstr* instr) {
-  VisitBinaryIntegerOp(instr);
-}
-
-
-void ConstantPropagator::VisitShiftMintOp(ShiftMintOpInstr* instr) {
-  VisitBinaryIntegerOp(instr);
-}
-
-
-void ConstantPropagator::VisitBoxInt64(BoxInt64Instr* instr) {
-  // TODO(kmillikin): Handle box operation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnboxInt64(UnboxInt64Instr* instr) {
-  // TODO(kmillikin): Handle unbox operation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnaryMintOp(UnaryMintOpInstr* instr) {
-  // TODO(kmillikin): Handle unary operations.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnarySmiOp(UnarySmiOpInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    // TODO(kmillikin): Handle unary operations.
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitUnaryDoubleOp(UnaryDoubleOpInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    // TODO(kmillikin): Handle unary operations.
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitSmiToDouble(SmiToDoubleInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsConstant(value) && value.IsInteger()) {
-    SetValue(instr, Double::Handle(I,
-        Double::New(Integer::Cast(value).AsDoubleValue(), Heap::kOld)));
-  } else if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitMintToDouble(MintToDoubleInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsConstant(value) && value.IsInteger()) {
-    SetValue(instr, Double::Handle(I,
-        Double::New(Integer::Cast(value).AsDoubleValue(), Heap::kOld)));
-  } else if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitInt32ToDouble(Int32ToDoubleInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsConstant(value) && value.IsInteger()) {
-    SetValue(instr, Double::Handle(I,
-        Double::New(Integer::Cast(value).AsDoubleValue(), Heap::kOld)));
-  } else if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitDoubleToInteger(DoubleToIntegerInstr* instr) {
-  // TODO(kmillikin): Handle conversion.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitDoubleToSmi(DoubleToSmiInstr* instr) {
-  // TODO(kmillikin): Handle conversion.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitDoubleToDouble(DoubleToDoubleInstr* instr) {
-  // TODO(kmillikin): Handle conversion.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitDoubleToFloat(DoubleToFloatInstr* instr) {
-  // TODO(kmillikin): Handle conversion.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloatToDouble(FloatToDoubleInstr* instr) {
-  // TODO(kmillikin): Handle conversion.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInvokeMathCFunction(
-    InvokeMathCFunctionInstr* instr) {
-  // TODO(kmillikin): Handle conversion.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitMergedMath(MergedMathInstr* instr) {
-  // TODO(srdjan): Handle merged instruction.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitExtractNthOutput(ExtractNthOutputInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitConstant(ConstantInstr* instr) {
-  SetValue(instr, instr->value());
-}
-
-
-void ConstantPropagator::VisitUnboxedConstant(UnboxedConstantInstr* instr) {
-  SetValue(instr, instr->value());
-}
-
-
-void ConstantPropagator::VisitConstraint(ConstraintInstr* instr) {
-  // Should not be used outside of range analysis.
-  UNREACHABLE();
-}
-
-
-void ConstantPropagator::VisitMaterializeObject(MaterializeObjectInstr* instr) {
-  // Should not be used outside of allocation elimination pass.
-  UNREACHABLE();
-}
-
-
-static bool IsIntegerOrDouble(const Object& value) {
-  return value.IsInteger() || value.IsDouble();
-}
-
-
-static double ToDouble(const Object& value) {
-  return value.IsInteger() ? Integer::Cast(value).AsDoubleValue()
-                           : Double::Cast(value).value();
-}
-
-
-void ConstantPropagator::VisitBinaryDoubleOp(
-    BinaryDoubleOpInstr* instr) {
-  const Object& left = instr->left()->definition()->constant_value();
-  const Object& right = instr->right()->definition()->constant_value();
-  if (IsNonConstant(left) || IsNonConstant(right)) {
-    SetValue(instr, non_constant_);
-  } else if (left.IsInteger() && right.IsInteger()) {
-    SetValue(instr, non_constant_);
-  } else if (IsIntegerOrDouble(left) && IsIntegerOrDouble(right)) {
-    const double left_val = ToDouble(left);
-    const double right_val = ToDouble(right);
-    double result_val = 0.0;
-    switch (instr->op_kind()) {
-      case Token::kADD:
-        result_val = left_val + right_val;
-        break;
-      case Token::kSUB:
-        result_val = left_val - right_val;
-        break;
-      case Token::kMUL:
-        result_val = left_val * right_val;
-        break;
-      case Token::kDIV:
-        result_val = left_val / right_val;
-        break;
-      default:
-        UNREACHABLE();
-    }
-    const Double& result = Double::ZoneHandle(Double::NewCanonical(result_val));
-    SetValue(instr, result);
-  }
-}
-
-
-void ConstantPropagator::VisitBinaryFloat32x4Op(
-    BinaryFloat32x4OpInstr* instr) {
-  const Object& left = instr->left()->definition()->constant_value();
-  const Object& right = instr->right()->definition()->constant_value();
-  if (IsNonConstant(left) || IsNonConstant(right)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(left) && IsConstant(right)) {
-    // TODO(kmillikin): Handle binary operation.
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitFloat32x4Constructor(
-    Float32x4ConstructorInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitSimd32x4Shuffle(Simd32x4ShuffleInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitSimd32x4ShuffleMix(
-    Simd32x4ShuffleMixInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitSimd32x4GetSignMask(
-    Simd32x4GetSignMaskInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4Zero(Float32x4ZeroInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4Splat(Float32x4SplatInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4Comparison(
-    Float32x4ComparisonInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4MinMax(Float32x4MinMaxInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4Scale(Float32x4ScaleInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4Sqrt(Float32x4SqrtInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4ZeroArg(Float32x4ZeroArgInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4Clamp(Float32x4ClampInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4With(Float32x4WithInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4ToInt32x4(
-    Float32x4ToInt32x4Instr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInt32x4Constructor(
-    Int32x4ConstructorInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInt32x4BoolConstructor(
-    Int32x4BoolConstructorInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInt32x4GetFlag(Int32x4GetFlagInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInt32x4SetFlag(Int32x4SetFlagInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInt32x4Select(Int32x4SelectInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitInt32x4ToFloat32x4(
-    Int32x4ToFloat32x4Instr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitBinaryInt32x4Op(BinaryInt32x4OpInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitSimd64x2Shuffle(Simd64x2ShuffleInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitBinaryFloat64x2Op(BinaryFloat64x2OpInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat32x4ToFloat64x2(
-    Float32x4ToFloat64x2Instr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat64x2ToFloat32x4(
-    Float64x2ToFloat32x4Instr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat64x2Zero(
-    Float64x2ZeroInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat64x2Splat(
-    Float64x2SplatInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat64x2Constructor(
-    Float64x2ConstructorInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat64x2ZeroArg(Float64x2ZeroArgInstr* instr) {
-  // TODO(johnmccutchan): Implement constant propagation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitFloat64x2OneArg(Float64x2OneArgInstr* instr) {
-  // TODO(johnmccutchan): Implement constant propagation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitMathUnary(MathUnaryInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    // TODO(kmillikin): Handle Math's unary operations (sqrt, cos, sin).
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitMathMinMax(MathMinMaxInstr* instr) {
-  const Object& left = instr->left()->definition()->constant_value();
-  const Object& right = instr->right()->definition()->constant_value();
-  if (IsNonConstant(left) || IsNonConstant(right)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(left) && IsConstant(right)) {
-    // TODO(srdjan): Handle min and max.
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitCaseInsensitiveCompareUC16(
-    CaseInsensitiveCompareUC16Instr *instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnbox(UnboxInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    // TODO(kmillikin): Handle conversion.
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitBox(BoxInstr* instr) {
-  const Object& value = instr->value()->definition()->constant_value();
-  if (IsNonConstant(value)) {
-    SetValue(instr, non_constant_);
-  } else if (IsConstant(value)) {
-    // TODO(kmillikin): Handle conversion.
-    SetValue(instr, non_constant_);
-  }
-}
-
-
-void ConstantPropagator::VisitBoxUint32(BoxUint32Instr* instr) {
-  // TODO(kmillikin): Handle box operation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnboxUint32(UnboxUint32Instr* instr) {
-  // TODO(kmillikin): Handle unbox operation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitBoxInt32(BoxInt32Instr* instr) {
-  // TODO(kmillikin): Handle box operation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnboxInt32(UnboxInt32Instr* instr) {
-  // TODO(kmillikin): Handle unbox operation.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnboxedIntConverter(
-    UnboxedIntConverterInstr* instr) {
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::VisitUnaryUint32Op(UnaryUint32OpInstr* instr) {
-  // TODO(kmillikin): Handle unary operations.
-  SetValue(instr, non_constant_);
-}
-
-
-void ConstantPropagator::Analyze() {
-  GraphEntryInstr* entry = graph_->graph_entry();
-  reachable_->Add(entry->preorder_number());
-  block_worklist_.Add(entry);
-
-  while (true) {
-    if (block_worklist_.is_empty()) {
-      if (definition_worklist_.IsEmpty()) break;
-      Definition* definition = definition_worklist_.RemoveLast();
-      Value* use = definition->input_use_list();
-      while (use != NULL) {
-        use->instruction()->Accept(this);
-        use = use->next_use();
-      }
-    } else {
-      BlockEntryInstr* block = block_worklist_.RemoveLast();
-      block->Accept(this);
-    }
-  }
-}
-
-
-static bool IsEmptyBlock(BlockEntryInstr* block) {
-  return block->next()->IsGoto() &&
-      (!block->IsJoinEntry() || (block->AsJoinEntry()->phis() == NULL)) &&
-      !block->IsIndirectEntry();
-}
-
-
-// Traverses a chain of empty blocks and returns the first reachable non-empty
-// block that is not dominated by the start block. The empty blocks are added
-// to the supplied bit vector.
-static BlockEntryInstr* FindFirstNonEmptySuccessor(
-    TargetEntryInstr* block,
-    BitVector* empty_blocks) {
-  BlockEntryInstr* current = block;
-  while (IsEmptyBlock(current) && block->Dominates(current)) {
-    ASSERT(!block->IsJoinEntry() || (block->AsJoinEntry()->phis() == NULL));
-    empty_blocks->Add(current->preorder_number());
-    current = current->next()->AsGoto()->successor();
-  }
-  return current;
-}
-
-
-void ConstantPropagator::EliminateRedundantBranches() {
-  // Canonicalize branches that have no side-effects and where true- and
-  // false-targets are the same.
-  bool changed = false;
-  BitVector* empty_blocks = new(I) BitVector(I, graph_->preorder().length());
-  for (BlockIterator b = graph_->postorder_iterator();
-       !b.Done();
-       b.Advance()) {
-    BlockEntryInstr* block = b.Current();
-    BranchInstr* branch = block->last_instruction()->AsBranch();
-    empty_blocks->Clear();
-    if ((branch != NULL) && branch->Effects().IsNone()) {
-      ASSERT(branch->previous() != NULL);  // Not already eliminated.
-      BlockEntryInstr* if_true =
-          FindFirstNonEmptySuccessor(branch->true_successor(), empty_blocks);
-      BlockEntryInstr* if_false =
-          FindFirstNonEmptySuccessor(branch->false_successor(), empty_blocks);
-      if (if_true == if_false) {
-        // Replace the branch with a jump to the common successor.
-        // Drop the comparison, which does not have side effects
-        JoinEntryInstr* join = if_true->AsJoinEntry();
-        if (join->phis() == NULL) {
-          GotoInstr* jump = new(I) GotoInstr(if_true->AsJoinEntry());
-          jump->InheritDeoptTarget(I, branch);
-
-          Instruction* previous = branch->previous();
-          branch->set_previous(NULL);
-          previous->LinkTo(jump);
-
-          // Remove uses from branch and all the empty blocks that
-          // are now unreachable.
-          branch->UnuseAllInputs();
-          for (BitVector::Iterator it(empty_blocks); !it.Done(); it.Advance()) {
-            BlockEntryInstr* empty_block = graph_->preorder()[it.Current()];
-            empty_block->ClearAllInstructions();
-          }
-
-          changed = true;
-
-          if (FLAG_trace_constant_propagation) {
-            OS::Print("Eliminated branch in B%" Pd " common target B%" Pd "\n",
-                      block->block_id(), join->block_id());
-          }
-        }
-      }
-    }
-  }
-
-  if (changed) {
-    graph_->DiscoverBlocks();
-    // TODO(fschneider): Update dominator tree in place instead of recomputing.
-    GrowableArray<BitVector*> dominance_frontier;
-    graph_->ComputeDominators(&dominance_frontier);
-  }
-}
-
-
-void ConstantPropagator::Transform() {
-  if (FLAG_trace_constant_propagation) {
-    OS::Print("\n==== Before constant propagation ====\n");
-    FlowGraphPrinter printer(*graph_);
-    printer.PrintBlocks();
-  }
-
-  // We will recompute dominators, block ordering, block ids, block last
-  // instructions, previous pointers, predecessors, etc. after eliminating
-  // unreachable code.  We do not maintain those properties during the
-  // transformation.
-  for (BlockIterator b = graph_->reverse_postorder_iterator();
-       !b.Done();
-       b.Advance()) {
-    BlockEntryInstr* block = b.Current();
-    if (!reachable_->Contains(block->preorder_number())) {
-      if (FLAG_trace_constant_propagation) {
-        OS::Print("Unreachable B%" Pd "\n", block->block_id());
-      }
-      // Remove all uses in unreachable blocks.
-      block->ClearAllInstructions();
-      continue;
-    }
-
-    JoinEntryInstr* join = block->AsJoinEntry();
-    if (join != NULL) {
-      // Remove phi inputs corresponding to unreachable predecessor blocks.
-      // Predecessors will be recomputed (in block id order) after removing
-      // unreachable code so we merely have to keep the phi inputs in order.
-      ZoneGrowableArray<PhiInstr*>* phis = join->phis();
-      if ((phis != NULL) && !phis->is_empty()) {
-        intptr_t pred_count = join->PredecessorCount();
-        intptr_t live_count = 0;
-        for (intptr_t pred_idx = 0; pred_idx < pred_count; ++pred_idx) {
-          if (reachable_->Contains(
-                  join->PredecessorAt(pred_idx)->preorder_number())) {
-            if (live_count < pred_idx) {
-              for (PhiIterator it(join); !it.Done(); it.Advance()) {
-                PhiInstr* phi = it.Current();
-                ASSERT(phi != NULL);
-                phi->SetInputAt(live_count, phi->InputAt(pred_idx));
-              }
-            }
-            ++live_count;
-          } else {
-            for (PhiIterator it(join); !it.Done(); it.Advance()) {
-              PhiInstr* phi = it.Current();
-              ASSERT(phi != NULL);
-              phi->InputAt(pred_idx)->RemoveFromUseList();
-            }
-          }
-        }
-        if (live_count < pred_count) {
-          intptr_t to_idx = 0;
-          for (intptr_t from_idx = 0; from_idx < phis->length(); ++from_idx) {
-            PhiInstr* phi = (*phis)[from_idx];
-            ASSERT(phi != NULL);
-            if (FLAG_remove_redundant_phis && (live_count == 1)) {
-              Value* input = phi->InputAt(0);
-              phi->ReplaceUsesWith(input->definition());
-              input->RemoveFromUseList();
-            } else {
-              phi->inputs_.TruncateTo(live_count);
-              (*phis)[to_idx++] = phi;
-            }
-          }
-          if (to_idx == 0) {
-            join->phis_ = NULL;
-          } else {
-            phis->TruncateTo(to_idx);
-          }
-        }
-      }
-    }
-
-    for (ForwardInstructionIterator i(block); !i.Done(); i.Advance()) {
-      Definition* defn = i.Current()->AsDefinition();
-      // Replace constant-valued instructions without observable side
-      // effects.  Do this for smis only to avoid having to copy other
-      // objects into the heap's old generation.
-      if ((defn != NULL) &&
-          IsConstant(defn->constant_value()) &&
-          (defn->constant_value().IsSmi() || defn->constant_value().IsOld()) &&
-          !defn->IsConstant() &&
-          !defn->IsPushArgument() &&
-          !defn->IsStoreIndexed() &&
-          !defn->IsStoreInstanceField() &&
-          !defn->IsStoreStaticField()) {
-        if (FLAG_trace_constant_propagation) {
-          OS::Print("Constant v%" Pd " = %s\n",
-                    defn->ssa_temp_index(),
-                    defn->constant_value().ToCString());
-        }
-        ConstantInstr* constant = graph_->GetConstant(defn->constant_value());
-        defn->ReplaceUsesWith(constant);
-        i.RemoveCurrentFromGraph();
-      }
-    }
-
-    // Replace branches where one target is unreachable with jumps.
-    BranchInstr* branch = block->last_instruction()->AsBranch();
-    if (branch != NULL) {
-      TargetEntryInstr* if_true = branch->true_successor();
-      TargetEntryInstr* if_false = branch->false_successor();
-      JoinEntryInstr* join = NULL;
-      Instruction* next = NULL;
-
-      if (!reachable_->Contains(if_true->preorder_number())) {
-        ASSERT(reachable_->Contains(if_false->preorder_number()));
-        ASSERT(if_false->parallel_move() == NULL);
-        ASSERT(if_false->loop_info() == NULL);
-        join = new(I) JoinEntryInstr(if_false->block_id(),
-                                     if_false->try_index());
-        join->InheritDeoptTarget(I, if_false);
-        if_false->UnuseAllInputs();
-        next = if_false->next();
-      } else if (!reachable_->Contains(if_false->preorder_number())) {
-        ASSERT(if_true->parallel_move() == NULL);
-        ASSERT(if_true->loop_info() == NULL);
-        join = new(I) JoinEntryInstr(if_true->block_id(),
-                                     if_true->try_index());
-        join->InheritDeoptTarget(I, if_true);
-        if_true->UnuseAllInputs();
-        next = if_true->next();
-      }
-
-      if (join != NULL) {
-        // Replace the branch with a jump to the reachable successor.
-        // Drop the comparison, which does not have side effects as long
-        // as it is a strict compare (the only one we can determine is
-        // constant with the current analysis).
-        GotoInstr* jump = new(I) GotoInstr(join);
-        jump->InheritDeoptTarget(I, branch);
-
-        Instruction* previous = branch->previous();
-        branch->set_previous(NULL);
-        previous->LinkTo(jump);
-
-        // Replace the false target entry with the new join entry. We will
-        // recompute the dominators after this pass.
-        join->LinkTo(next);
-        branch->UnuseAllInputs();
-      }
-    }
-  }
-
-  graph_->DiscoverBlocks();
-  graph_->MergeBlocks();
-  GrowableArray<BitVector*> dominance_frontier;
-  graph_->ComputeDominators(&dominance_frontier);
-
-  if (FLAG_trace_constant_propagation) {
-    OS::Print("\n==== After constant propagation ====\n");
-    FlowGraphPrinter printer(*graph_);
-    printer.PrintBlocks();
-  }
-}
-
-
 // Returns true if the given phi has a single input use and
 // is used in the environments either at the corresponding block entry or
 // at the same instruction where input use is.