Switch to a fix-point based range analysis to improve its precision.

runtime/vm/flow_graph_range_analysis.cc

Index: runtime/vm/flow_graph_range_analysis.cc
diff --git a/runtime/vm/flow_graph_range_analysis.cc b/runtime/vm/flow_graph_range_analysis.cc
index ff95ed041e7a6e1450e5ba271ab8c931bd06d577..7be32d14f3e697897e6314a68208ecb2895b7ba5 100644
--- a/runtime/vm/flow_graph_range_analysis.cc
+++ b/runtime/vm/flow_graph_range_analysis.cc
@@ -23,8 +23,12 @@ void RangeAnalysis::Analyze() {
   CollectValues();
   InsertConstraints();
   InferRanges();
+  EliminateRedundantBoundsChecks();
+  MarkUnreachableBlocks();
+
   IntegerInstructionSelector iis(flow_graph_);
   iis.Select();
+
   RemoveConstraints();
 }
 
@@ -85,7 +89,13 @@ void RangeAnalysis::CollectValues() {
           values_.Add(defn);
         }
       } else if (current->IsCheckSmi()) {
+        if (current->Canonicalize(flow_graph_) == NULL) {
+          instr_it.RemoveCurrentFromGraph();
+          continue;
+        }
         smi_checks_.Add(current->AsCheckSmi());
+      } else if (current->IsCheckArrayBound()) {
+        bounds_checks_.Add(current->AsCheckArrayBound());
       }
     }
   }
@@ -166,7 +176,7 @@ Range* RangeAnalysis::ConstraintRange(Token::Kind op, Definition* boundary) {
       return new(I) Range(RangeBoundary::FromDefinition(boundary),
                           RangeBoundary::FromDefinition(boundary));
     case Token::kNE:
-      return Range::Unknown();
+      return new(I) Range(Range::Full(RangeBoundary::kRangeBoundarySmi));
     case Token::kLT:
       return new(I) Range(RangeBoundary::MinSmi(),
                           RangeBoundary::FromDefinition(boundary, -1));
@@ -181,7 +191,7 @@ Range* RangeAnalysis::ConstraintRange(Token::Kind op, Definition* boundary) {
                           RangeBoundary::MaxSmi());
     default:
       UNREACHABLE();
-      return Range::Unknown();
+      return NULL;
   }
 }
 
@@ -192,7 +202,18 @@ ConstraintInstr* RangeAnalysis::InsertConstraintFor(Definition* defn,
   // No need to constrain constants.
   if (defn->IsConstant()) return NULL;
 
-  ConstraintInstr* constraint = new(I) ConstraintInstr(
+  // Check if the value is already constrained to avoid inserting duplicated
+  // constraints.
+  ConstraintInstr* constraint = after->next()->AsConstraint();
+  while (constraint != NULL) {
+    if ((constraint->value()->definition() == defn) &&
+        constraint->constraint()->Equals(constraint_range)) {
+      return NULL;
+    }
+    constraint = constraint->next()->AsConstraint();
+  }
+
+  constraint = new(I) ConstraintInstr(
       new(I) Value(defn), constraint_range);
   flow_graph_->InsertAfter(after, constraint, NULL, FlowGraph::kValue);
   RenameDominatedUses(defn, constraint, constraint);
@@ -284,16 +305,23 @@ void RangeAnalysis::ConstrainValueAfterCheckArrayBound(
 
 
 void RangeAnalysis::InsertConstraints() {
+  Range* smi_range = new(I) Range(
+      Range::Full(RangeBoundary::kRangeBoundarySmi));
+
   for (intptr_t i = 0; i < smi_checks_.length(); i++) {
     CheckSmiInstr* check = smi_checks_[i];
     ConstraintInstr* constraint =
         InsertConstraintFor(check->value()->definition(),
-                            Range::UnknownSmi(),
+                            smi_range,
                             check);
     if (constraint == NULL) {
       // No constraint was needed.
       continue;
     }
+    if (!check->value()->definition()->IsBoxInteger()) {
+      constraint->set_range(Range::Full(RangeBoundary::kRangeBoundarySmi));
+    }
+
     // Mark the constraint's value's reaching type as smi.
     CompileType* smi_compile_type =
         ZoneCompileType::Wrap(CompileType::FromCid(kSmiCid));
@@ -310,220 +338,303 @@ void RangeAnalysis::InsertConstraints() {
 }
 
 
-void RangeAnalysis::ResetWorklist() {
-  if (marked_defns_ == NULL) {
-    marked_defns_ = new(I) BitVector(flow_graph_->current_ssa_temp_index());
-  } else {
-    marked_defns_->Clear();
+static Definition* UnwrapConstraint(Definition* defn) {
+  while (defn->IsConstraint()) {
+    defn = defn->AsConstraint()->value()->definition();
   }
-  worklist_.Clear();
+  return defn;
 }
 
 
-void RangeAnalysis::MarkDefinition(Definition* defn) {
-  // Unwrap constrained value.
-  while (defn->IsConstraint()) {
-    defn = defn->AsConstraint()->value()->definition();
-  }
+static bool AreEqualDefinitions(Definition* a, Definition* b) {
+  a = UnwrapConstraint(a);
+  b = UnwrapConstraint(b);
+  return (a == b) ||
+      (a->AllowsCSE() &&
+       a->Dependencies().IsNone() &&
+       b->AllowsCSE() &&
+       b->Dependencies().IsNone() &&
+       a->Equals(b));
+}
 
-  if (!marked_defns_->Contains(defn->ssa_temp_index())) {
-    worklist_.Add(defn);
-    marked_defns_->Add(defn->ssa_temp_index());
-  }
+
+static bool DependOnSameSymbol(const RangeBoundary& a, const RangeBoundary& b) {
+  return a.IsSymbol() && b.IsSymbol() &&
+      AreEqualDefinitions(a.symbol(), b.symbol());
 }
 
 
-RangeAnalysis::Direction RangeAnalysis::ToDirection(Value* val) {
-  if (val->BindsToConstant()) {
-    return (Smi::Cast(val->BoundConstant()).Value() >= 0) ? kPositive
-                                                          : kNegative;
-  } else if (val->definition()->range() != NULL) {
-    Range* range = val->definition()->range();
-    if (Range::ConstantMin(range).ConstantValue() >= 0) {
-      return kPositive;
-    } else if (Range::ConstantMax(range).ConstantValue() <= 0) {
-      return kNegative;
+// Given the current range of a phi and a newly computed range check
+// if it is growing towards negative infinity, if it does widen it to
+// MinSmi.
+static RangeBoundary WidenMin(const Range* range, const Range* new_range) {
+  RangeBoundary min = range->min();
+  RangeBoundary new_min = new_range->min();
+
+  if (min.IsSymbol()) {
+    if (min.LowerBound().OverflowedSmi()) {
+      return RangeBoundary::MinSmi();
+    } else if (DependOnSameSymbol(min, new_min)) {
+      return min.offset() <= new_min.offset() ? min : RangeBoundary::MinSmi();
+    } else if (min.SmiUpperBound() <= new_min.SmiLowerBound()) {
+      return min;
     }
   }
-  return kUnknown;
-}
 
+  min = Range::ConstantMinSmi(range);
+  new_min = Range::ConstantMinSmi(new_range);
 
-Range* RangeAnalysis::InferInductionVariableRange(JoinEntryInstr* loop_header,
-                                                  PhiInstr* var) {
-  BitVector* loop_info = loop_header->loop_info();
+  return (min.ConstantValue() <= new_min.ConstantValue()) ?
+      min : RangeBoundary::MinSmi();
+}
 
-  Definition* initial_value = NULL;
-  Direction direction = kUnknown;
+// Given the current range of a phi and a newly computed range check
+// if it is growing towards positive infinity, if it does widen it to
+// MaxSmi.
+static RangeBoundary WidenMax(const Range* range, const Range* new_range) {
+  RangeBoundary max = range->max();
+  RangeBoundary new_max = new_range->max();
 
-  ResetWorklist();
-  MarkDefinition(var);
-  while (!worklist_.is_empty()) {
-    Definition* defn = worklist_.RemoveLast();
+  if (max.IsSymbol()) {
+    if (max.UpperBound().OverflowedSmi()) {
+      return RangeBoundary::MaxSmi();
+    } else if (DependOnSameSymbol(max, new_max)) {
+      return max.offset() >= new_max.offset() ? max : RangeBoundary::MaxSmi();
+    } else if (max.SmiLowerBound() >= new_max.SmiUpperBound()) {
+      return max;
+    }
+  }
 
-    if (defn->IsPhi()) {
-      PhiInstr* phi = defn->AsPhi();
-      for (intptr_t i = 0; i < phi->InputCount(); i++) {
-        Definition* defn = phi->InputAt(i)->definition();
+  max = Range::ConstantMaxSmi(range);
+  new_max = Range::ConstantMaxSmi(new_range);
 
-        if (!loop_info->Contains(defn->GetBlock()->preorder_number())) {
-          // The value is coming from outside of the loop.
-          if (initial_value == NULL) {
-            initial_value = defn;
-            continue;
-          } else if (initial_value == defn) {
-            continue;
-          } else {
-            return NULL;
-          }
-        }
+  return (max.ConstantValue() >= new_max.ConstantValue()) ?
+      max : RangeBoundary::MaxSmi();
+}
 
-        MarkDefinition(defn);
-      }
-    } else if (defn->IsBinarySmiOp()) {
-      BinarySmiOpInstr* binary_op = defn->AsBinarySmiOp();
-
-      switch (binary_op->op_kind()) {
-        case Token::kADD: {
-          const Direction growth_right =
-              ToDirection(binary_op->right());
-          if (growth_right != kUnknown) {
-            UpdateDirection(&direction, growth_right);
-            MarkDefinition(binary_op->left()->definition());
-            break;
-          }
 
-          const Direction growth_left =
-              ToDirection(binary_op->left());
-          if (growth_left != kUnknown) {
-            UpdateDirection(&direction, growth_left);
-            MarkDefinition(binary_op->right()->definition());
-            break;
-          }
+// Given the current range of a phi and a newly computed range check
+// if we can perform narrowing: use newly computed minimum to improve precision
+// of the computed range. We do it only if current minimum was widened and is
+// equal to MinSmi.
+// Newly computed minimum is expected to be greater of equal then old one as
+// we are running after widening phase.
+static RangeBoundary NarrowMin(const Range* range, const Range* new_range) {
+#ifdef DEBUG
+  const RangeBoundary min = Range::ConstantMinSmi(range);
+  const RangeBoundary new_min = Range::ConstantMinSmi(new_range);
+  ASSERT(min.ConstantValue() <= new_min.ConstantValue());
+#endif
+  // TODO(vegorov): consider using negative infinity to indicate widened bound.
+  return range->min().IsSmiMinimumOrBelow() ? new_range->min() : range->min();
+}
 
-          return NULL;
-        }
 
-        case Token::kSUB: {
-          const Direction growth_right =
-              ToDirection(binary_op->right());
-          if (growth_right != kUnknown) {
-            UpdateDirection(&direction, Invert(growth_right));
-            MarkDefinition(binary_op->left()->definition());
-            break;
-          }
-          return NULL;
-        }
+// Given the current range of a phi and a newly computed range check
+// if we can perform narrowing: use newly computed maximum to improve precision
+// of the computed range. We do it only if current maximum was widened and is
+// equal to MaxSmi.
+// Newly computed minimum is expected to be greater of equal then old one as
+// we are running after widening phase.
+static RangeBoundary NarrowMax(const Range* range, const Range* new_range) {
+#ifdef DEBUG
+  const RangeBoundary max = Range::ConstantMaxSmi(range);
+  const RangeBoundary new_max = Range::ConstantMaxSmi(new_range);
+  ASSERT(max.ConstantValue() >= new_max.ConstantValue());
+#endif
+  // TODO(vegorov): consider using positive infinity to indicate widened bound.
+  return range->max().IsSmiMaximumOrAbove() ? new_range->max() : range->max();
+}
 
-        default:
-          return NULL;
+
+char RangeAnalysis::OpPrefix(JoinOperator op) {
+  switch (op) {
+    case WIDEN: return 'W';
+    case NARROW: return 'N';
+    case NONE: return 'I';
+  }
+  UNREACHABLE();
+  return ' ';
+}
+
+
+bool RangeAnalysis::InferRange(JoinOperator op,
+                               Definition* defn,
+                               intptr_t iteration) {
+  Range range;
+  defn->InferRange(&range);
+
+  if (!Range::IsUnknown(&range)) {
+    if (!Range::IsUnknown(defn->range()) && defn->IsPhi()) {
+      // TODO(vegorov): we are currently supporting only smi phis.
+      ASSERT(defn->Type()->ToCid() == kSmiCid);
+      if (op == WIDEN) {
+        range = Range(WidenMin(defn->range(), &range),
+                      WidenMax(defn->range(), &range));
+      } else if (op == NARROW) {
+        range = Range(NarrowMin(defn->range(), &range),
+                      NarrowMax(defn->range(), &range));
       }
-    } else {
-      return NULL;
     }
-  }
 
-
-  // We transitively discovered all dependencies of the given phi
-  // and confirmed that it depends on a single value coming from outside of
-  // the loop and some linear combinations of itself.
-  // Compute the range based on initial value and the direction of the growth.
-  switch (direction) {
-    case kPositive:
-      return new(I) Range(RangeBoundary::FromDefinition(initial_value),
-                          RangeBoundary::MaxSmi());
-
-    case kNegative:
-      return new(I) Range(RangeBoundary::MinSmi(),
-                          RangeBoundary::FromDefinition(initial_value));
-
-    case kUnknown:
-    case kBoth:
-      return Range::UnknownSmi();
+    if (!range.Equals(defn->range())) {
+      if (FLAG_trace_range_analysis) {
+        OS::Print("%c [%" Pd "] %s:  %s => %s\n",
+                  OpPrefix(op),
+                  iteration,
+                  defn->ToCString(),
+                  Range::ToCString(defn->range()),
+                  Range::ToCString(&range));
+      }
+      defn->set_range(range);
+      return true;
+    }
   }
 
-  UNREACHABLE();
-  return NULL;
+  return false;
 }
 
 
-void RangeAnalysis::InferRangesRecursive(BlockEntryInstr* block) {
+void RangeAnalysis::CollectDefinitionsRecursive(BlockEntryInstr* block,
+                                                BitVector* set) {
   JoinEntryInstr* join = block->AsJoinEntry();
   if (join != NULL) {
-    const bool is_loop_header = (join->loop_info() != NULL);
     for (PhiIterator it(join); !it.Done(); it.Advance()) {
       PhiInstr* phi = it.Current();
-      if (definitions_->Contains(phi->ssa_temp_index())) {
-        if (is_loop_header) {
-          // Try recognizing simple induction variables.
-          Range* range = InferInductionVariableRange(join, phi);
-          if (range != NULL) {
-            phi->range_ = range;
-            continue;
-          }
-        }
-
-        phi->InferRange();
+      if (set->Contains(phi->ssa_temp_index())) {
+        definitions_.Add(phi);
       }
     }
   }
 
   for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
-    Instruction* current = it.Current();
-
-    Definition* defn = current->AsDefinition();
+    Definition* defn = it.Current()->AsDefinition();
     if ((defn != NULL) &&
         (defn->ssa_temp_index() != -1) &&
-        definitions_->Contains(defn->ssa_temp_index())) {
-      defn->InferRange();
-    } else if (FLAG_array_bounds_check_elimination &&
-               current->IsCheckArrayBound()) {
-      CheckArrayBoundInstr* check = current->AsCheckArrayBound();
-      RangeBoundary array_length =
-          RangeBoundary::FromDefinition(check->length()->definition());
-      if (check->IsRedundant(array_length)) {
-        it.RemoveCurrentFromGraph();
-      }
+        set->Contains(defn->ssa_temp_index())) {
+      definitions_.Add(defn);
     }
   }
 
   for (intptr_t i = 0; i < block->dominated_blocks().length(); ++i) {
-    InferRangesRecursive(block->dominated_blocks()[i]);
+    CollectDefinitionsRecursive(block->dominated_blocks()[i], set);

[Florian Schneider, 2014/08/15 11:58:02]

Why recursive and dominator-tree order? Wouldn't reverse post-order be better
for reaching a fixed point faster because it all blocks are visited before their
successors?

   }
 }
 
 
+void RangeAnalysis::Iterate(JoinOperator op, intptr_t max_iterations) {
+  intptr_t iteration = 0;
+  bool changed;
+  do {
+    changed = false;
+    for (intptr_t i = 0; i < definitions_.length(); i++) {

[Florian Schneider, 2014/08/15 11:58:01]

Consider using a worklist-based iteration instead, if iterating over all
definitions turns out to be a performance issue. Maybe add a TODO.

+      Definition* defn = definitions_[i];
+      if (InferRange(op, defn, iteration)) {
+        changed = true;
+      }
+    }
+
+    iteration++;
+  } while (changed && (iteration < max_iterations));
+}
+
+
 void RangeAnalysis::InferRanges() {
   if (FLAG_trace_range_analysis) {
-    OS::Print("---- before range analysis -------\n");
-    FlowGraphPrinter printer(*flow_graph_);
-    printer.PrintBlocks();
+    FlowGraphPrinter::PrintGraph("Range Analysis (BEFORE)", flow_graph_);
   }
+
   // Initialize bitvector for quick filtering of int values.
-  definitions_ =
-      new(I) BitVector(flow_graph_->current_ssa_temp_index());
+  BitVector* set = new(I) BitVector(flow_graph_->current_ssa_temp_index());
   for (intptr_t i = 0; i < values_.length(); i++) {
-    definitions_->Add(values_[i]->ssa_temp_index());
+    set->Add(values_[i]->ssa_temp_index());
   }
   for (intptr_t i = 0; i < constraints_.length(); i++) {
-    definitions_->Add(constraints_[i]->ssa_temp_index());
+    set->Add(constraints_[i]->ssa_temp_index());
   }
 
-  // Infer initial values of ranges.
+  // Collect integer definitions (including constraints) in the dominator tree
+  // traversal order. This improves convergence speed compared to iterating
+  // values_ and constraints_ array separately.
   const GrowableArray<Definition*>& initial =
       *flow_graph_->graph_entry()->initial_definitions();
   for (intptr_t i = 0; i < initial.length(); ++i) {
     Definition* definition = initial[i];
-    if (definitions_->Contains(definition->ssa_temp_index())) {
-      definition->InferRange();
+    if (set->Contains(definition->ssa_temp_index())) {
+      definitions_.Add(definition);
     }
   }
-  InferRangesRecursive(flow_graph_->graph_entry());
+  CollectDefinitionsRecursive(flow_graph_->graph_entry(), set);
+
+  // Perform an iteration of range inference just propagating ranges
+  // through the graph as-is without applying widening or narrowing.
+  // This helps to improve precision of initial bounds.
+  Iterate(NONE, 1);
+
+  // Perform fix-point iteration of range inference applying widening
+  // operator to phis to ensure fast convergence.
+  // Widening simply maps growing bounds to the respective range bound.
+  Iterate(WIDEN, kMaxInt32);
 
   if (FLAG_trace_range_analysis) {
-    OS::Print("---- after range analysis -------\n");
-    FlowGraphPrinter printer(*flow_graph_);
-    printer.PrintBlocks();
+    FlowGraphPrinter::PrintGraph("Range Analysis (WIDEN)", flow_graph_);
+  }
+
+  // Perform fix-point iteration of range inference applying narrowing
+  // to phis to compute more accurate range.
+  // Narrowing only improves those boundaries that were widened up to
+  // range boundary and leaves other boundaries intact.
+  Iterate(NARROW, kMaxInt32);
+
+  if (FLAG_trace_range_analysis) {
+    FlowGraphPrinter::PrintGraph("Range Analysis (AFTER)", flow_graph_);
+  }
+}
+
+
+void RangeAnalysis::EliminateRedundantBoundsChecks() {
+  if (FLAG_array_bounds_check_elimination) {
+    for (intptr_t i = 0; i < bounds_checks_.length(); i++) {
+      CheckArrayBoundInstr* check = bounds_checks_[i];
+      RangeBoundary array_length =
+          RangeBoundary::FromDefinition(check->length()->definition());
+      if (check->IsRedundant(array_length)) {
+        check->RemoveFromGraph();
+      }
+    }
+  }
+}
+
+
+void RangeAnalysis::MarkUnreachableBlocks() {
+  for (intptr_t i = 0; i < constraints_.length(); i++) {
+    if (Range::IsUnknown(constraints_[i]->range())) {
+      TargetEntryInstr* target = constraints_[i]->target();
+      if (target == NULL) {
+        // TODO(vegorov): replace Constraint with an uncoditional
+        // deoptimization and kill all dominated dead code.
+        continue;
+      }
+
+      BranchInstr* branch =
+          target->PredecessorAt(0)->last_instruction()->AsBranch();
+      if (target == branch->true_successor()) {
+        // True unreachable.
+        if (FLAG_trace_constant_propagation) {
+          OS::Print("Range analysis: True unreachable (B%" Pd ")\n",
+                    branch->true_successor()->block_id());
+        }
+        branch->set_constant_target(branch->false_successor());
+      } else {
+        ASSERT(target == branch->false_successor());
+        // False unreachable.
+        if (FLAG_trace_constant_propagation) {
+          OS::Print("Range analysis: False unreachable (B%" Pd ")\n",
+                    branch->false_successor()->block_id());
+        }
+        branch->set_constant_target(branch->true_successor());
+      }
+    }
   }
 }
 
@@ -807,7 +918,7 @@ RangeBoundary RangeBoundary::LowerBound() const {
     return NegativeInfinity();
   }
   if (IsConstant()) return *this;
-  return Add(Range::ConstantMin(symbol()->range()),
+  return Add(Range::ConstantMinSmi(symbol()->range()),
              RangeBoundary::FromConstant(offset_),
              NegativeInfinity());
 }
@@ -818,7 +929,8 @@ RangeBoundary RangeBoundary::UpperBound() const {
     return PositiveInfinity();
   }
   if (IsConstant()) return *this;
-  return Add(Range::ConstantMax(symbol()->range()),
+
+  return Add(Range::ConstantMaxSmi(symbol()->range()),
              RangeBoundary::FromConstant(offset_),
              PositiveInfinity());
 }
@@ -891,33 +1003,6 @@ bool RangeBoundary::SymbolicSub(const RangeBoundary& a,
 }
 
 
-static Definition* UnwrapConstraint(Definition* defn) {
-  while (defn->IsConstraint()) {
-    defn = defn->AsConstraint()->value()->definition();
-  }
-  return defn;
-}
-
-
-static bool AreEqualDefinitions(Definition* a, Definition* b) {
-  a = UnwrapConstraint(a);
-  b = UnwrapConstraint(b);
-  return (a == b) ||
-      (a->AllowsCSE() &&
-       a->Dependencies().IsNone() &&
-       b->AllowsCSE() &&
-       b->Dependencies().IsNone() &&
-       a->Equals(b));
-}
-
-
-// Returns true if two range boundaries refer to the same symbol.
-static bool DependOnSameSymbol(const RangeBoundary& a, const RangeBoundary& b) {
-  return a.IsSymbol() && b.IsSymbol() &&
-      AreEqualDefinitions(a.symbol(), b.symbol());
-}
-
-
 bool RangeBoundary::Equals(const RangeBoundary& other) const {
   if (IsConstant() && other.IsConstant()) {
     return ConstantValue() == other.ConstantValue();
@@ -1057,118 +1142,143 @@ static bool CanonicalizeMinBoundary(RangeBoundary* a) {
   return true;
 }
 
+typedef bool (*BoundaryOp)(RangeBoundary*);
 
-RangeBoundary RangeBoundary::Min(RangeBoundary a, RangeBoundary b,
-                                 RangeSize size) {
-  ASSERT(!(a.IsNegativeInfinity() || b.IsNegativeInfinity()));
-  ASSERT(!a.IsUnknown() || !b.IsUnknown());
-  if (a.IsUnknown() && !b.IsUnknown()) {
-    return b;
+static bool CanonicalizeForComparison(RangeBoundary* a,
+                                      RangeBoundary* b,
+                                      BoundaryOp op,
+                                      const RangeBoundary& overflow) {
+  if (!a->IsSymbol() || !b->IsSymbol()) {
+    return false;
   }
-  if (!a.IsUnknown() && b.IsUnknown()) {
-    return a;
+
+  if (DependOnSameSymbol(*a, *b)) {
+    return true;
   }
-  if (size == kRangeBoundarySmi) {
-    if (a.IsSmiMaximumOrAbove() && !b.IsSmiMaximumOrAbove()) {
-      return b;
-    }
-    if (!a.IsSmiMaximumOrAbove() && b.IsSmiMaximumOrAbove()) {
-      return a;
-    }
-  } else {
-    ASSERT(size == kRangeBoundaryInt64);
-    if (a.IsMaximumOrAbove() && !b.IsMaximumOrAbove()) {
-      return b;
-    }
-    if (!a.IsMaximumOrAbove() && b.IsMaximumOrAbove()) {
-      return a;
+
+
+  RangeBoundary canonical_a = CanonicalizeBoundary(*a, overflow);
+  RangeBoundary canonical_b = CanonicalizeBoundary(*b, overflow);
+
+  do {
+    if (DependOnSameSymbol(canonical_a, canonical_b)) {
+      *a = canonical_a;
+      *b = canonical_b;
+      return true;
     }
-  }
+  } while (op(&canonical_a) || op(&canonical_b));
+
+  return false;
+}
 
+
+RangeBoundary RangeBoundary::JoinMin(RangeBoundary a, RangeBoundary b) {
   if (a.Equals(b)) {
     return b;
   }
 
-  {
-    RangeBoundary canonical_a =
-        CanonicalizeBoundary(a, RangeBoundary::PositiveInfinity());
-    RangeBoundary canonical_b =
-        CanonicalizeBoundary(b, RangeBoundary::PositiveInfinity());
-    do {
-      if (DependOnSameSymbol(canonical_a, canonical_b)) {
-        a = canonical_a;
-        b = canonical_b;
-        break;
-      }
-    } while (CanonicalizeMaxBoundary(&canonical_a) ||
-             CanonicalizeMaxBoundary(&canonical_b));
-  }
-
-  if (DependOnSameSymbol(a, b)) {
+  if (CanonicalizeForComparison(&a,
+                                &b,
+                                &CanonicalizeMinBoundary,
+                                RangeBoundary::NegativeInfinity())) {
     return (a.offset() <= b.offset()) ? a : b;
   }
 
-  const int64_t min_a = a.UpperBound().Clamp(size).ConstantValue();
-  const int64_t min_b = b.UpperBound().Clamp(size).ConstantValue();
+  const int64_t inf_a = a.SmiLowerBound();
+  const int64_t inf_b = b.SmiLowerBound();
+  const int64_t sup_a = a.SmiUpperBound();
+  const int64_t sup_b = b.SmiUpperBound();
 
-  return RangeBoundary::FromConstant(Utils::Minimum(min_a, min_b));
+  if ((sup_a <= inf_b) && !a.LowerBound().OverflowedSmi()) {
+    return a;
+  } else if ((sup_b <= inf_a) && !b.LowerBound().OverflowedSmi()) {
+    return b;
+  } else {
+    return RangeBoundary::FromConstant(Utils::Minimum(inf_a, inf_b));
+  }
 }
 
 
-RangeBoundary RangeBoundary::Max(RangeBoundary a, RangeBoundary b,
-                                 RangeSize size) {
-  ASSERT(!(a.IsPositiveInfinity() || b.IsPositiveInfinity()));
-  ASSERT(!a.IsUnknown() || !b.IsUnknown());
-  if (a.IsUnknown() && !b.IsUnknown()) {
+RangeBoundary RangeBoundary::JoinMax(RangeBoundary a, RangeBoundary b) {
+  if (a.Equals(b)) {
     return b;
   }
-  if (!a.IsUnknown() && b.IsUnknown()) {
-    return a;
+
+  if (CanonicalizeForComparison(&a,
+                                &b,
+                                &CanonicalizeMaxBoundary,
+                                RangeBoundary::PositiveInfinity())) {
+    return (a.offset() >= b.offset()) ? a : b;
   }
-  if (size == kRangeBoundarySmi) {
-    if (a.IsSmiMinimumOrBelow() && !b.IsSmiMinimumOrBelow()) {
-      return b;
-    }
-    if (!a.IsSmiMinimumOrBelow() && b.IsSmiMinimumOrBelow()) {
-      return a;
-    }
+
+  const int64_t inf_a = a.SmiLowerBound();
+  const int64_t inf_b = b.SmiLowerBound();
+  const int64_t sup_a = a.SmiUpperBound();
+  const int64_t sup_b = b.SmiUpperBound();
+
+  if ((sup_a <= inf_b) && !b.UpperBound().OverflowedSmi()) {
+    return b;
+  } else if ((sup_b <= inf_a) && !a.UpperBound().OverflowedSmi()) {
+    return a;
   } else {
-     ASSERT(size == kRangeBoundaryInt64);
-    if (a.IsMinimumOrBelow() && !b.IsMinimumOrBelow()) {
-      return b;
-    }
-    if (!a.IsMinimumOrBelow() && b.IsMinimumOrBelow()) {
-      return a;
-    }
+    return RangeBoundary::FromConstant(Utils::Maximum(sup_a, sup_b));
   }
+}
+
+
+RangeBoundary RangeBoundary::IntersectionMin(RangeBoundary a, RangeBoundary b) {
+  ASSERT(!a.IsPositiveInfinity() && !b.IsPositiveInfinity());
+  ASSERT(!a.IsUnknown() && !b.IsUnknown());
+
   if (a.Equals(b)) {
+    return a;
+  }
+
+  if (a.IsSmiMinimumOrBelow()) {
     return b;
+  } else if (b.IsSmiMinimumOrBelow()) {
+    return a;
   }
 
-  {
-    RangeBoundary canonical_a =
-        CanonicalizeBoundary(a, RangeBoundary::NegativeInfinity());
-    RangeBoundary canonical_b =
-        CanonicalizeBoundary(b, RangeBoundary::NegativeInfinity());
+  if (CanonicalizeForComparison(&a,
+                                &b,
+                                &CanonicalizeMinBoundary,
+                                RangeBoundary::NegativeInfinity())) {
+    return (a.offset() >= b.offset()) ? a : b;
+  }
 
-    do {
-      if (DependOnSameSymbol(canonical_a, canonical_b)) {
-        a = canonical_a;
-        b = canonical_b;
-        break;
-      }
-    } while (CanonicalizeMinBoundary(&canonical_a) ||
-             CanonicalizeMinBoundary(&canonical_b));
+  const int64_t inf_a = a.SmiLowerBound();
+  const int64_t inf_b = b.SmiLowerBound();
+
+  return (inf_a >= inf_b) ? a : b;
+}
+
+
+RangeBoundary RangeBoundary::IntersectionMax(RangeBoundary a, RangeBoundary b) {
+  ASSERT(!a.IsNegativeInfinity() && !b.IsNegativeInfinity());
+  ASSERT(!a.IsUnknown() && !b.IsUnknown());
+
+  if (a.Equals(b)) {
+    return a;
+  }
+
+  if (a.IsSmiMaximumOrAbove()) {
+    return b;
+  } else if (b.IsSmiMaximumOrAbove()) {
+    return a;
   }
 
-  if (DependOnSameSymbol(a, b)) {
-    return (a.offset() <= b.offset()) ? b : a;
+  if (CanonicalizeForComparison(&a,
+                                &b,
+                                &CanonicalizeMaxBoundary,
+                                RangeBoundary::PositiveInfinity())) {
+    return (a.offset() <= b.offset()) ? a : b;
   }
 
-  const int64_t max_a = a.LowerBound().Clamp(size).ConstantValue();
-  const int64_t max_b = b.LowerBound().Clamp(size).ConstantValue();
+  const int64_t sup_a = a.SmiUpperBound();
+  const int64_t sup_b = b.SmiUpperBound();
 
-  return RangeBoundary::FromConstant(Utils::Maximum(max_a, max_b));
+  return (sup_a <= sup_b) ? a : b;
 }
 
 
@@ -1353,7 +1463,7 @@ static bool IsArrayLength(Definition* defn) {
   if (defn == NULL) {
     return false;
   }
-  LoadFieldInstr* load = defn->AsLoadField();
+  LoadFieldInstr* load = UnwrapConstraint(defn)->AsLoadField();
   return (load != NULL) && load->IsImmutableLengthLoad();
 }
 
@@ -1445,6 +1555,14 @@ bool Range::Mul(const Range* left_range,
       return true;
     }
   }
+
+  if (OnlyPositiveOrZero(*left_range, *right_range) ||
+      OnlyNegativeOrZero(*left_range, *right_range)) {

[Florian Schneider, 2014/08/15 11:58:02]

Do you think it's worth handling the mixed sign cases as well? Maybe add a TODO
for now

+    *result_min = RangeBoundary::FromConstant(0);
+    *result_max = RangeBoundary::PositiveInfinity();
+    return true;
+  }
+
   return false;
 }
 
@@ -1472,10 +1590,11 @@ int64_t Range::ConstantAbsMax(const Range* range) {
 }
 
 
-Range* Range::BinaryOp(const Token::Kind op,
-                       const Range* left_range,
-                       const Range* right_range,
-                       Definition* left_defn) {
+void Range::BinaryOp(const Token::Kind op,
+                     const Range* left_range,
+                     const Range* right_range,
+                     Definition* left_defn,
+                     Range* result) {
   ASSERT(left_range != NULL);
   ASSERT(right_range != NULL);
 
@@ -1496,7 +1615,8 @@ Range* Range::BinaryOp(const Token::Kind op,
       break;
     case Token::kMUL: {
       if (!Range::Mul(left_range, right_range, &min, &max)) {
-        return NULL;
+        *result = Range::Full(RangeBoundary::kRangeBoundaryInt64);
+        return;
       }
       break;
     }
@@ -1510,29 +1630,34 @@ Range* Range::BinaryOp(const Token::Kind op,
     }
     case Token::kBIT_AND:
       if (!Range::And(left_range, right_range, &min, &max)) {
-        return NULL;
+        *result = Range::Full(RangeBoundary::kRangeBoundaryInt64);
+        return;
       }
       break;
     default:
-      return NULL;
-      break;
+      *result = Range::Full(RangeBoundary::kRangeBoundaryInt64);
+      return;
   }
 
   ASSERT(!min.IsUnknown() && !max.IsUnknown());
 
-  return new Range(min, max);
+  *result = Range(min, max);
 }
 
 
-void Definition::InferRange() {
+void Definition::set_range(const Range& range) {
+  if (range_ == NULL) {
+    range_ = new Range();
+  }
+  *range_ = range;
+}
+
+
+void Definition::InferRange(Range* range) {
   if (Type()->ToCid() == kSmiCid) {
-    if (range_ == NULL) {
-      range_ = Range::UnknownSmi();
-    }
+    *range = Range::Full(RangeBoundary::kRangeBoundarySmi);
   } else if (IsMintDefinition()) {
-    if (range_ == NULL) {
-      range_ = Range::Unknown();
-    }
+    *range = Range::Full(RangeBoundary::kRangeBoundaryInt64);
   } else {
     // Only Smi and Mint supported.
     UNREACHABLE();
@@ -1540,59 +1665,112 @@ void Definition::InferRange() {
 }
 
 
-void PhiInstr::InferRange() {
-  RangeBoundary new_min;
-  RangeBoundary new_max;
+static bool DependsOnSymbol(const RangeBoundary& a, Definition* symbol) {
+  return a.IsSymbol() && (UnwrapConstraint(a.symbol()) == symbol);
+}
 
-  ASSERT(Type()->ToCid() == kSmiCid);
 
-  for (intptr_t i = 0; i < InputCount(); i++) {
-    Range* input_range = InputAt(i)->definition()->range();
-    if (input_range == NULL) {
-      range_ = Range::UnknownSmi();
-      return;
-    }
+// Given the range and definition update the range so that
+// it covers both original range and defintions range.
+//
+// The following should also hold:
+//
+//     [_|_, _|_] U a = a U [_|_, _|_] = a
+//
+static void Join(Range* range, Definition* defn) {
+  if (Range::IsUnknown(defn->range())) {
+    return;
+  }
 
-    if (new_min.IsUnknown()) {
-      new_min = Range::ConstantMin(input_range);
-    } else {
-      new_min = RangeBoundary::Min(new_min,
-                                   Range::ConstantMinSmi(input_range),
-                                   RangeBoundary::kRangeBoundarySmi);
-    }
+  if (Range::IsUnknown(range)) {
+    *range = *defn->range();
+    return;
+  }
 
-    if (new_max.IsUnknown()) {
-      new_max = Range::ConstantMax(input_range);
-    } else {
-      new_max = RangeBoundary::Max(new_max,
-                                   Range::ConstantMaxSmi(input_range),
-                                   RangeBoundary::kRangeBoundarySmi);
-    }
+  Range other = *defn->range();
+
+  // Handle patterns where range already depends on defn as a symbol:
+  //
+  //    (..., S+o] U range(S) and [S+o, ...) U range(S)
+  //
+  // To improve precision of the computed join use [S, S] instead of
+  // using range(S). It will be canonicalized away by JoinMin/JoinMax
+  // functions.
+  Definition* unwrapped = UnwrapConstraint(defn);
+  if (DependsOnSymbol(range->min(), unwrapped) ||
+      DependsOnSymbol(range->max(), unwrapped)) {
+    other = Range(RangeBoundary::FromDefinition(defn, 0),
+                  RangeBoundary::FromDefinition(defn, 0));
+  }
+
+  // First try to compare ranges based on their upper and lower bounds.
+  const int64_t inf_range = range->min().SmiLowerBound();
+  const int64_t inf_other = other.min().SmiLowerBound();
+  const int64_t sup_range = range->max().SmiUpperBound();
+  const int64_t sup_other = other.max().SmiUpperBound();
+
+  if (sup_range <= inf_other) {
+    // The range is fully below defn's range. Keep the minimum and
+    // expand the maximum.
+    range->set_max(other.max());
+  } else if (sup_other <= inf_range) {
+    // The range is fully above defn's range. Keep the maximum and
+    // expand the minimum.
+    range->set_min(other.min());
+  } else {
+    // Can't compare ranges as whole. Join minimum and maximum separately.
+    *range = Range(RangeBoundary::JoinMin(range->min(), other.min()),
+                   RangeBoundary::JoinMax(range->max(), other.max()));
   }
+}
 
-  ASSERT(new_min.IsUnknown() == new_max.IsUnknown());
-  if (new_min.IsUnknown()) {
-    range_ = Range::UnknownSmi();
-    return;
+
+// When assigning range to a phi we must take care to avoid self-reference
+// cycles when phi's range depends on the phi itself.
+// To prevent such cases we impose additional restriction on symbols that
+// can be used as boundaries for phi's range: they must dominate
+// phi's definition.
+static RangeBoundary EnsureAcyclicSymbol(BlockEntryInstr* phi_block,
+                                         const RangeBoundary& a,
+                                         const RangeBoundary& limit) {
+  if (!a.IsSymbol() || a.symbol()->GetBlock()->Dominates(phi_block)) {
+    return a;
+  }
+
+  // Symbol does not dominate phi. Try unwrapping constraint and check again.
+  Definition* unwrapped = UnwrapConstraint(a.symbol());
+  if ((unwrapped != a.symbol()) &&
+      unwrapped->GetBlock()->Dominates(phi_block)) {
+    return RangeBoundary::FromDefinition(unwrapped, a.offset());
+  }
+
+  return limit;
+}
+
+
+void PhiInstr::InferRange(Range* range) {
+  ASSERT(Type()->ToCid() == kSmiCid);
+  for (intptr_t i = 0; i < InputCount(); i++) {
+    Join(range, InputAt(i)->definition());
   }
 
-  range_ = new Range(new_min, new_max);
+  BlockEntryInstr* phi_block = GetBlock();
+  range->set_min(EnsureAcyclicSymbol(
+      phi_block, range->min(), RangeBoundary::MinSmi()));
+  range->set_max(EnsureAcyclicSymbol(
+      phi_block, range->max(), RangeBoundary::MaxSmi()));
 }
 
 
-void ConstantInstr::InferRange() {
+void ConstantInstr::InferRange(Range* range) {
   if (value_.IsSmi()) {
-    if (range_ == NULL) {
-      int64_t value = Smi::Cast(value_).Value();
-      range_ = new Range(RangeBoundary::FromConstant(value),
-                         RangeBoundary::FromConstant(value));
-    }
+    int64_t value = Smi::Cast(value_).Value();
+    *range = Range(RangeBoundary::FromConstant(value),
+                   RangeBoundary::FromConstant(value));
   } else if (value_.IsMint()) {
-    if (range_ == NULL) {
-      int64_t value = Mint::Cast(value_).value();
-      range_ = new Range(RangeBoundary::FromConstant(value),
-                         RangeBoundary::FromConstant(value));
-    }
+    int64_t value = Mint::Cast(value_).value();
+    *range = Range(RangeBoundary::FromConstant(value),
+                   RangeBoundary::FromConstant(value));
   } else {
     // Only Smi and Mint supported.
     UNREACHABLE();
@@ -1600,160 +1778,114 @@ void ConstantInstr::InferRange() {
 }
 
 
-void UnboxIntegerInstr::InferRange() {
-  if (range_ == NULL) {
-    Definition* unboxed = value()->definition();
-    ASSERT(unboxed != NULL);
-    Range* range = unboxed->range();
-    if (range == NULL) {
-      range_ = Range::Unknown();
-      return;
-    }
-    range_ = new Range(range->min(), range->max());
-  }
-}
-
-
-void ConstraintInstr::InferRange() {
-  Range* value_range = value()->definition()->range();
-
+void ConstraintInstr::InferRange(Range* range) {
   // Only constraining smi values.
   ASSERT(value()->IsSmiValue());
 
-  RangeBoundary min;
-  RangeBoundary max;
-
-  {
-    RangeBoundary value_min = (value_range == NULL) ?
-        RangeBoundary() : value_range->min();
-    RangeBoundary constraint_min = constraint()->min();
-    min = RangeBoundary::Max(value_min, constraint_min,
-                             RangeBoundary::kRangeBoundarySmi);
+  Range* value_range = value()->definition()->range();
+  if (Range::IsUnknown(value_range)) {
+    return;
   }
 
-  ASSERT(!min.IsUnknown());
-
-  {
-    RangeBoundary value_max = (value_range == NULL) ?
-        RangeBoundary() : value_range->max();
-    RangeBoundary constraint_max = constraint()->max();
-    max = RangeBoundary::Min(value_max, constraint_max,
-                             RangeBoundary::kRangeBoundarySmi);
+  // TODO(vegorov) check if precision of the analysis can be improved by
+  // recognizing intersections of the form:
+  //
+  //       (..., S+x] ^ [S+x, ...) = [S+x, S+x]
+  //
+  Range result = value_range->Intersect(constraint());
+  if (result.IsUnsatisfiable()) {
+    return;
   }
 
-  ASSERT(!max.IsUnknown());
+  *range = result;
+}
 
-  range_ = new Range(min, max);
 
-  // Mark branches that generate unsatisfiable constraints as constant.
-  if (target() != NULL && range_->IsUnsatisfiable()) {
-    BranchInstr* branch =
-        target()->PredecessorAt(0)->last_instruction()->AsBranch();
-    if (target() == branch->true_successor()) {
-      // True unreachable.
-      if (FLAG_trace_constant_propagation) {
-        OS::Print("Range analysis: True unreachable (B%" Pd ")\n",
-                  branch->true_successor()->block_id());
-      }
-      branch->set_constant_target(branch->false_successor());
-    } else {
-      ASSERT(target() == branch->false_successor());
-      // False unreachable.
-      if (FLAG_trace_constant_propagation) {
-        OS::Print("Range analysis: False unreachable (B%" Pd ")\n",
-                  branch->false_successor()->block_id());
-      }
-      branch->set_constant_target(branch->true_successor());
-    }
-  }
-}
+void LoadFieldInstr::InferRange(Range* range) {
+  switch (recognized_kind()) {
+    case MethodRecognizer::kObjectArrayLength:
+    case MethodRecognizer::kImmutableArrayLength:
+      *range = Range(RangeBoundary::FromConstant(0),
+                     RangeBoundary::FromConstant(Array::kMaxElements));
+      break;
 
+    case MethodRecognizer::kTypedDataLength:
+      *range = Range(RangeBoundary::FromConstant(0), RangeBoundary::MaxSmi());
+      break;
 
-void LoadFieldInstr::InferRange() {
-  if ((range_ == NULL) &&
-      ((recognized_kind() == MethodRecognizer::kObjectArrayLength) ||
-       (recognized_kind() == MethodRecognizer::kImmutableArrayLength))) {
-    range_ = new Range(RangeBoundary::FromConstant(0),
-                       RangeBoundary::FromConstant(Array::kMaxElements));
-    return;
-  }
-  if ((range_ == NULL) &&
-      (recognized_kind() == MethodRecognizer::kTypedDataLength)) {
-    range_ = new Range(RangeBoundary::FromConstant(0), RangeBoundary::MaxSmi());
-    return;
-  }
-  if ((range_ == NULL) &&
-      (recognized_kind() == MethodRecognizer::kStringBaseLength)) {
-    range_ = new Range(RangeBoundary::FromConstant(0),
-                       RangeBoundary::FromConstant(String::kMaxElements));
-    return;
+    case MethodRecognizer::kStringBaseLength:
+      *range = Range(RangeBoundary::FromConstant(0),
+                     RangeBoundary::FromConstant(String::kMaxElements));
+      break;
+
+    default:
+      Definition::InferRange(range);
   }
-  Definition::InferRange();
 }
 
 
 
-void LoadIndexedInstr::InferRange() {
+void LoadIndexedInstr::InferRange(Range* range) {
   switch (class_id()) {
     case kTypedDataInt8ArrayCid:
-      range_ = new Range(RangeBoundary::FromConstant(-128),
-                         RangeBoundary::FromConstant(127));
+      *range = Range(RangeBoundary::FromConstant(-128),
+                     RangeBoundary::FromConstant(127));
       break;
     case kTypedDataUint8ArrayCid:
     case kTypedDataUint8ClampedArrayCid:
     case kExternalTypedDataUint8ArrayCid:
     case kExternalTypedDataUint8ClampedArrayCid:
-      range_ = new Range(RangeBoundary::FromConstant(0),
-                         RangeBoundary::FromConstant(255));
+      *range = Range(RangeBoundary::FromConstant(0),
+                     RangeBoundary::FromConstant(255));
       break;
     case kTypedDataInt16ArrayCid:
-      range_ = new Range(RangeBoundary::FromConstant(-32768),
-                         RangeBoundary::FromConstant(32767));
+      *range = Range(RangeBoundary::FromConstant(-32768),
+                     RangeBoundary::FromConstant(32767));
       break;
     case kTypedDataUint16ArrayCid:
-      range_ = new Range(RangeBoundary::FromConstant(0),
-                         RangeBoundary::FromConstant(65535));
+      *range = Range(RangeBoundary::FromConstant(0),
+                     RangeBoundary::FromConstant(65535));
       break;
     case kTypedDataInt32ArrayCid:
       if (Typed32BitIsSmi()) {
-        range_ = Range::UnknownSmi();
+        *range = Range::Full(RangeBoundary::kRangeBoundarySmi);
       } else {
-        range_ = new Range(RangeBoundary::FromConstant(kMinInt32),
-                           RangeBoundary::FromConstant(kMaxInt32));
+        *range = Range(RangeBoundary::FromConstant(kMinInt32),
+                       RangeBoundary::FromConstant(kMaxInt32));
       }
       break;
     case kTypedDataUint32ArrayCid:
       if (Typed32BitIsSmi()) {
-        range_ = Range::UnknownSmi();
+        *range = Range::Full(RangeBoundary::kRangeBoundarySmi);
       } else {
-        range_ = new Range(RangeBoundary::FromConstant(0),
-                           RangeBoundary::FromConstant(kMaxUint32));
+        *range = Range(RangeBoundary::FromConstant(0),
+                       RangeBoundary::FromConstant(kMaxUint32));
       }
       break;
     case kOneByteStringCid:
-      range_ = new Range(RangeBoundary::FromConstant(0),
-                         RangeBoundary::FromConstant(0xFF));
+      *range = Range(RangeBoundary::FromConstant(0),
+                     RangeBoundary::FromConstant(0xFF));
       break;
     case kTwoByteStringCid:
-      range_ = new Range(RangeBoundary::FromConstant(0),
-                         RangeBoundary::FromConstant(0xFFFF));
+      *range = Range(RangeBoundary::FromConstant(0),
+                     RangeBoundary::FromConstant(0xFFFF));
       break;
     default:
-      Definition::InferRange();
+      Definition::InferRange(range);
       break;
   }
 }
 
 
-void IfThenElseInstr::InferRange() {
+void IfThenElseInstr::InferRange(Range* range) {
   const intptr_t min = Utils::Minimum(if_true_, if_false_);
   const intptr_t max = Utils::Maximum(if_true_, if_false_);
-  range_ = new Range(RangeBoundary::FromConstant(min),
-                     RangeBoundary::FromConstant(max));
+  *range = Range(RangeBoundary::FromConstant(min),
+                 RangeBoundary::FromConstant(max));
 }
 
 
-void BinarySmiOpInstr::InferRange() {
+void BinarySmiOpInstr::InferRange(Range* range) {
   // TODO(vegorov): canonicalize BinarySmiOp to always have constant on the
   // right and a non-constant on the left.
   Definition* left_defn = left()->definition();
@@ -1761,41 +1893,28 @@ void BinarySmiOpInstr::InferRange() {
   Range* left_range = left_defn->range();
   Range* right_range = right()->definition()->range();
 
-  if ((left_range == NULL) || (right_range == NULL)) {
-    range_ = Range::UnknownSmi();
-    return;
-  }
-
-  Range* possible_range = Range::BinaryOp(op_kind(),
-                                          left_range,
-                                          right_range,
-                                          left_defn);
-
-  if ((range_ == NULL) && (possible_range == NULL)) {
-    // Initialize.
-    range_ = Range::UnknownSmi();
+  if (Range::IsUnknown(left_range) || Range::IsUnknown(right_range)) {
     return;
   }
 
-  if (possible_range == NULL) {
-    // Nothing new.
-    return;
-  }
-
-  range_ = possible_range;
+  Range::BinaryOp(op_kind(),
+                  left_range,
+                  right_range,
+                  left_defn,
+                  range);
+  ASSERT(!Range::IsUnknown(range));
 
-  ASSERT(!range_->min().IsUnknown() && !range_->max().IsUnknown());
   // Calculate overflowed status before clamping.
-  const bool overflowed = range_->min().LowerBound().OverflowedSmi() ||
-                          range_->max().UpperBound().OverflowedSmi();
+  const bool overflowed = range->min().LowerBound().OverflowedSmi() ||
+                          range->max().UpperBound().OverflowedSmi();
   set_overflow(overflowed);
 
   // Clamp value to be within smi range.
-  range_->Clamp(RangeBoundary::kRangeBoundarySmi);
+  range->Clamp(RangeBoundary::kRangeBoundarySmi);
 }
 
 
-void BinaryMintOpInstr::InferRange() {
+void BinaryMintOpInstr::InferRange(Range* range) {
   // TODO(vegorov): canonicalize BinaryMintOpInstr to always have constant on
   // the right and a non-constant on the left.
   Definition* left_defn = left()->definition();
@@ -1803,90 +1922,73 @@ void BinaryMintOpInstr::InferRange() {
   Range* left_range = left_defn->range();
   Range* right_range = right()->definition()->range();
 
-  if ((left_range == NULL) || (right_range == NULL)) {
-    range_ = Range::Unknown();
+  if (Range::IsUnknown(left_range) || Range::IsUnknown(right_range)) {
     return;
   }
 
-  Range* possible_range = Range::BinaryOp(op_kind(),
-                                          left_range,
-                                          right_range,
-                                          left_defn);
-
-  if ((range_ == NULL) && (possible_range == NULL)) {
-    // Initialize.
-    range_ = Range::Unknown();
-    return;
-  }
-
-  if (possible_range == NULL) {
-    // Nothing new.
-    return;
-  }
-
-  range_ = possible_range;
-
-  ASSERT(!range_->min().IsUnknown() && !range_->max().IsUnknown());
+  Range::BinaryOp(op_kind(),
+                  left_range,
+                  right_range,
+                  left_defn,
+                  range);
+  ASSERT(!Range::IsUnknown(range));
 
   // Calculate overflowed status before clamping.
-  const bool overflowed = range_->min().LowerBound().OverflowedMint() ||
-                          range_->max().UpperBound().OverflowedMint();
+  const bool overflowed = range->min().LowerBound().OverflowedMint() ||
+                          range->max().UpperBound().OverflowedMint();
   set_can_overflow(overflowed);
 
   // Clamp value to be within mint range.
-  range_->Clamp(RangeBoundary::kRangeBoundaryInt64);
+  range->Clamp(RangeBoundary::kRangeBoundaryInt64);
 }
 
 
-void ShiftMintOpInstr::InferRange() {
+void ShiftMintOpInstr::InferRange(Range* range) {
   Definition* left_defn = left()->definition();
 
   Range* left_range = left_defn->range();
   Range* right_range = right()->definition()->range();
 
-  if ((left_range == NULL) || (right_range == NULL)) {
-    range_ = Range::Unknown();
+  if (Range::IsUnknown(left_range) || Range::IsUnknown(right_range)) {
     return;
   }
 
-  Range* possible_range = Range::BinaryOp(op_kind(),
-                                          left_range,
-                                          right_range,
-                                          left_defn);
-
-  if ((range_ == NULL) && (possible_range == NULL)) {
-    // Initialize.
-    range_ = Range::Unknown();
-    return;
-  }
-
-  if (possible_range == NULL) {
-    // Nothing new.
-    return;
-  }
-
-  range_ = possible_range;
-
-  ASSERT(!range_->min().IsUnknown() && !range_->max().IsUnknown());
+  Range::BinaryOp(op_kind(),
+                  left_range,
+                  right_range,
+                  left_defn,
+                  range);
+  ASSERT(!Range::IsUnknown(range));
 
   // Calculate overflowed status before clamping.
-  const bool overflowed = range_->min().LowerBound().OverflowedMint() ||
-                          range_->max().UpperBound().OverflowedMint();
+  const bool overflowed = range->min().LowerBound().OverflowedMint() ||
+                          range->max().UpperBound().OverflowedMint();
   set_can_overflow(overflowed);
 
   // Clamp value to be within mint range.
-  range_->Clamp(RangeBoundary::kRangeBoundaryInt64);
+  range->Clamp(RangeBoundary::kRangeBoundaryInt64);
 }
 
 
-void BoxIntegerInstr::InferRange() {
+void BoxIntegerInstr::InferRange(Range* range) {
   Range* input_range = value()->definition()->range();
   if (input_range != NULL) {
     bool is_smi = !input_range->min().LowerBound().OverflowedSmi() &&
                   !input_range->max().UpperBound().OverflowedSmi();
     set_is_smi(is_smi);
     // The output range is the same as the input range.
-    range_ = input_range;
+    *range = *input_range;
+  }
+}
+
+
+void UnboxIntegerInstr::InferRange(Range* range) {
+  Range* value_range = value()->definition()->range();
+  if (value_range != NULL) {
+    *range = *value_range;
+  } else if (!value()->definition()->IsMintDefinition() &&
+             (value()->Type()->ToCid() != kSmiCid)) {
+    *range = Range::Full(RangeBoundary::kRangeBoundaryInt64);
   }
 }