Fix issue 962.

SplitBetween (formely known as Split with 3 arguments) should select split position from [start, end] instead of [start, end[. This should also improve allocation quality (remove certain redundant move patterns).

Also some minor renaming and refactoring to make register allocator code more readable.

BUG=v8:962
TEST=test/mjsunit/regress/regress-962.js

Review URL: http://codereview.chromium.org/5720001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5969 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/lithium-allocator.cc

@@ -247,7 +247,7 @@ LOperand* LiveRange::CreateAssignedOperand() {
   LOperand* op = NULL;
   if (HasRegisterAssigned()) {
     ASSERT(!IsSpilled());
-    if (assigned_double_) {
+    if (IsDouble()) {
       op = LDoubleRegister::Create(assigned_register());
     } else {
       op = LRegister::Create(assigned_register());
@@ -290,7 +290,7 @@ void LiveRange::AdvanceLastProcessedMarker(
 
 
 void LiveRange::SplitAt(LifetimePosition position, LiveRange* result) {
-  ASSERT(Start().Value() <= position.Value());
+  ASSERT(Start().Value() < position.Value());
   ASSERT(result->IsEmpty());
   // Find the last interval that ends before the position. If the
   // position is contained in one of the intervals in the chain, we
@@ -625,7 +625,7 @@ LiveRange* LAllocator::FixedLiveRangeFor(int index) {
   if (result == NULL) {
     result = new LiveRange(FixedLiveRangeID(index));
     ASSERT(result->IsFixed());
-    result->set_assigned_register(index, false);
+    result->set_assigned_register(index, GENERAL_REGISTERS);
     fixed_live_ranges_[index] = result;
   }
   return result;
@@ -642,7 +642,7 @@ LiveRange* LAllocator::FixedDoubleLiveRangeFor(int index) {
   if (result == NULL) {
     result = new LiveRange(FixedDoubleLiveRangeID(index));
     ASSERT(result->IsFixed());
-    result->set_assigned_register(index, true);
+    result->set_assigned_register(index, DOUBLE_REGISTERS);
     fixed_double_live_ranges_[index] = result;
   }
   return result;
@@ -1258,14 +1258,6 @@ void LAllocator::BuildLiveRanges() {
 }
 
 
-void LAllocator::AllocateGeneralRegisters() {
-  HPhase phase("Allocate general registers", this);
-  num_registers_ = Register::kNumAllocatableRegisters;
-  mode_ = CPU_REGISTERS;
-  AllocateRegisters();
-}
-
-
 bool LAllocator::SafePointsAreInOrder() const {
   const ZoneList<LPointerMap*>* pointer_maps = chunk_->pointer_maps();
   int safe_point = 0;
@@ -1397,10 +1389,18 @@ void LAllocator::ProcessOsrEntry() {
 }
 
 
+void LAllocator::AllocateGeneralRegisters() {
+  HPhase phase("Allocate general registers", this);
+  num_registers_ = Register::kNumAllocatableRegisters;
+  mode_ = GENERAL_REGISTERS;
+  AllocateRegisters();
+}
+
+
 void LAllocator::AllocateDoubleRegisters() {
   HPhase phase("Allocate double registers", this);
   num_registers_ = DoubleRegister::kNumAllocatableRegisters;
-  mode_ = XMM_REGISTERS;
+  mode_ = DOUBLE_REGISTERS;
   AllocateRegisters();
 }
 
@@ -1411,7 +1411,7 @@ void LAllocator::AllocateRegisters() {
 
   for (int i = 0; i < live_ranges_.length(); ++i) {
     if (live_ranges_[i] != NULL) {
-      if (HasDoubleValue(live_ranges_[i]->id()) == (mode_ == XMM_REGISTERS)) {
+      if (RequiredRegisterKind(live_ranges_[i]->id()) == mode_) {
         AddToUnhandledUnsorted(live_ranges_[i]);
       }
     }
@@ -1422,7 +1422,7 @@ void LAllocator::AllocateRegisters() {
   ASSERT(active_live_ranges_.is_empty());
   ASSERT(inactive_live_ranges_.is_empty());
 
-  if (mode_ == XMM_REGISTERS) {
+  if (mode_ == DOUBLE_REGISTERS) {
     for (int i = 0; i < fixed_double_live_ranges_.length(); ++i) {
       LiveRange* current = fixed_double_live_ranges_.at(i);
       if (current != NULL) {
@@ -1463,11 +1463,7 @@ void LAllocator::AllocateRegisters() {
                  current->Start().NextInstruction().Value()) {
         // Do not spill live range eagerly if use position that can benefit from
         // the register is too close to the start of live range.
-        LiveRange* part = Split(current,
-                                current->Start().NextInstruction(),
-                                pos->pos());
-        Spill(current);
-        AddToUnhandledSorted(part);
+        SpillBetween(current, current->Start(), pos->pos());
         ASSERT(UnhandledIsSorted());
         continue;
       }
@@ -1521,6 +1517,16 @@ void LAllocator::Setup() {
 }
 
 
+const char* LAllocator::RegisterName(int allocation_index) {
+  ASSERT(mode_ != NONE);
+  if (mode_ == GENERAL_REGISTERS) {
+    return Register::AllocationIndexToString(allocation_index);
+  } else {
+    return DoubleRegister::AllocationIndexToString(allocation_index);
+  }
+}
+
+
 void LAllocator::TraceAlloc(const char* msg, ...) {
   if (FLAG_trace_alloc) {
     va_list arguments;
@@ -1544,10 +1550,12 @@ bool LAllocator::HasTaggedValue(int virtual_register) const {
 }
 
 
-bool LAllocator::HasDoubleValue(int virtual_register) const {
+RegisterKind LAllocator::RequiredRegisterKind(int virtual_register) const {
   HValue* value = graph()->LookupValue(virtual_register);
-  if (value == NULL) return false;
-  return value->representation().IsDouble();
+  if (value != NULL && value->representation().IsDouble()) {
+    return DOUBLE_REGISTERS;
+  }
+  return GENERAL_REGISTERS;
 }
 
 
@@ -1728,16 +1736,22 @@ void LAllocator::InactiveToActive(LiveRange* range) {
 }
 
 
+// TryAllocateFreeReg and AllocateBlockedReg assume this
+// when allocating local arrays.
+STATIC_ASSERT(DoubleRegister::kNumAllocatableRegisters >=
+              Register::kNumAllocatableRegisters);
+
+
 bool LAllocator::TryAllocateFreeReg(LiveRange* current) {
-  LifetimePosition max_pos = LifetimePosition::FromInstructionIndex(
-      chunk_->instructions()->length() + 1);
-  ASSERT(DoubleRegister::kNumAllocatableRegisters >=
-         Register::kNumAllocatableRegisters);
-  EmbeddedVector<LifetimePosition, DoubleRegister::kNumAllocatableRegisters>
-      free_pos(max_pos);
+  LifetimePosition free_until_pos[DoubleRegister::kNumAllocatableRegisters];
+
+  for (int i = 0; i < DoubleRegister::kNumAllocatableRegisters; i++) {
+    free_until_pos[i] = LifetimePosition::MaxPosition();
+  }
+
   for (int i = 0; i < active_live_ranges_.length(); ++i) {
     LiveRange* cur_active = active_live_ranges_.at(i);
-    free_pos[cur_active->assigned_register()] =
+    free_until_pos[cur_active->assigned_register()] =
         LifetimePosition::FromInstructionIndex(0);
   }
 
@@ -1748,65 +1762,83 @@ bool LAllocator::TryAllocateFreeReg(LiveRange* current) {
         cur_inactive->FirstIntersection(current);
     if (!next_intersection.IsValid()) continue;
     int cur_reg = cur_inactive->assigned_register();
-    free_pos[cur_reg] = Min(free_pos[cur_reg], next_intersection);
+    free_until_pos[cur_reg] = Min(free_until_pos[cur_reg], next_intersection);
   }
 
-  UsePosition* pos = current->FirstPosWithHint();
-  if (pos != NULL) {
-    LOperand* hint = pos->hint();
+  UsePosition* hinted_use = current->FirstPosWithHint();
+  if (hinted_use != NULL) {
+    LOperand* hint = hinted_use->hint();
     if (hint->IsRegister() || hint->IsDoubleRegister()) {
       int register_index = hint->index();
-      TraceAlloc("Found reg hint %d for live range %d (free [%d, end %d[)\n",
-                 register_index,
-                 current->id(),
-                 free_pos[register_index].Value(),
-                 current->End().Value());
-      if (free_pos[register_index].Value() >= current->End().Value()) {
-        TraceAlloc("Assigning preferred reg %d to live range %d\n",
-                   register_index,
+      TraceAlloc(
+          "Found reg hint %s (free until [%d) for live range %d (end %d[).\n",
+          RegisterName(register_index),
+          free_until_pos[register_index].Value(),
+          current->id(),
+          current->End().Value());
+
+      // The desired register is free until the end of the current live range.
+      if (free_until_pos[register_index].Value() >= current->End().Value()) {
+        TraceAlloc("Assigning preferred reg %s to live range %d\n",
+                   RegisterName(register_index),
                    current->id());
-        current->set_assigned_register(register_index, mode_ == XMM_REGISTERS);
+        current->set_assigned_register(register_index, mode_);
         return true;
       }
     }
   }
 
-  int max_reg = 0;
+  // Find the register which stays free for the longest time.
+  int reg = 0;
   for (int i = 1; i < RegisterCount(); ++i) {
-    if (free_pos[i].Value() > free_pos[max_reg].Value()) {
-      max_reg = i;
+    if (free_until_pos[i].Value() > free_until_pos[reg].Value()) {
+      reg = i;
     }
   }
 
-  if (free_pos[max_reg].InstructionIndex() == 0) {
+  LifetimePosition pos = free_until_pos[reg];
+
+  if (pos.Value() <= current->Start().Value()) {
+    // All registers are blocked.
     return false;
-  } else if (free_pos[max_reg].Value() >= current->End().Value()) {
-    TraceAlloc("Assigning reg %d to live range %d\n", max_reg, current->id());
-    current->set_assigned_register(max_reg, mode_ == XMM_REGISTERS);
-  } else {
-    // Split the interval before first use position of max_reg and never split
-    // it interval at its start position.
-    LifetimePosition pos = free_pos[max_reg];
-    if (pos.Value() <= current->Start().Value()) return false;
-    LiveRange* second_range = Split(current, pos);
-    AddToUnhandledSorted(second_range);
-    current->set_assigned_register(max_reg, mode_ == XMM_REGISTERS);
   }
 
+  if (pos.Value() < current->End().Value()) {
+    // Register reg is available at the range start but becomes blocked before
+    // the range end. Split current at position where it becomes blocked.
+    LiveRange* tail = SplitAt(current, pos);
+    AddToUnhandledSorted(tail);
+  }
+
+
+  // Register reg is available at the range start and is free until
+  // the range end.
+  ASSERT(pos.Value() >= current->End().Value());
+  TraceAlloc("Assigning reg %s to live range %d\n",
+             RegisterName(reg),
+             current->id());
+  current->set_assigned_register(reg, mode_);
+
   return true;
 }
 
 
 void LAllocator::AllocateBlockedReg(LiveRange* current) {
-  LifetimePosition max_pos =
-      LifetimePosition::FromInstructionIndex(
-          chunk_->instructions()->length() + 1);
-  ASSERT(DoubleRegister::kNumAllocatableRegisters >=
-         Register::kNumAllocatableRegisters);
-  EmbeddedVector<LifetimePosition, DoubleRegister::kNumAllocatableRegisters>
-      use_pos(max_pos);
-  EmbeddedVector<LifetimePosition, DoubleRegister::kNumAllocatableRegisters>
-      block_pos(max_pos);
+  UsePosition* register_use = current->NextRegisterPosition(current->Start());
+  if (register_use == NULL) {
+    // There is no use in the current live range that requires a register.
+    // We can just spill it.
+    Spill(current);
+    return;
+  }
+
+
+  LifetimePosition use_pos[DoubleRegister::kNumAllocatableRegisters];
+  LifetimePosition block_pos[DoubleRegister::kNumAllocatableRegisters];
+
+  for (int i = 0; i < DoubleRegister::kNumAllocatableRegisters; i++) {
+    use_pos[i] = block_pos[i] = LifetimePosition::MaxPosition();
+  }
 
   for (int i = 0; i < active_live_ranges_.length(); ++i) {
     LiveRange* range = active_live_ranges_[i];
@@ -1839,30 +1871,48 @@ void LAllocator::AllocateBlockedReg(LiveRange* current) {
     }
   }
 
-  int max_reg = 0;
+  int reg = 0;
   for (int i = 1; i < RegisterCount(); ++i) {
-    if (use_pos[i].Value() > use_pos[max_reg].Value()) {
-      max_reg = i;
+    if (use_pos[i].Value() > use_pos[reg].Value()) {
+      reg = i;
     }
   }
 
-  UsePosition* first_usage = current->NextRegisterPosition(current->Start());
-  if (first_usage == NULL) {
-    Spill(current);
-  } else if (use_pos[max_reg].Value() < first_usage->pos().Value()) {
-    SplitAndSpill(current, current->Start(), first_usage->pos());
-  } else {
-    if (block_pos[max_reg].Value() < current->End().Value()) {
-      // Split current before blocked position.
-      LiveRange* second_range = Split(current,
-                                      current->Start(),
-                                      block_pos[max_reg]);
-      AddToUnhandledSorted(second_range);
-    }
+  LifetimePosition pos = use_pos[reg];
+
+  if (pos.Value() < register_use->pos().Value()) {
+    // All registers are blocked before the first use that requires a register.
+    // Spill starting part of live range up to that use.
+    //
+    // Corner case: the first use position is equal to the start of the range.
+    // In this case we have nothing to spill and SpillBetween will just return
+    // this range to the list of unhandled ones. This will lead to the infinite
+    // loop.
+    ASSERT(current->Start().Value() < register_use->pos().Value());
+    SpillBetween(current, current->Start(), register_use->pos());
+    return;
+  }
 
-    current->set_assigned_register(max_reg, mode_ == XMM_REGISTERS);
-    SplitAndSpillIntersecting(current);
+  if (block_pos[reg].Value() < current->End().Value()) {
+    // Register becomes blocked before the current range end. Split before that
+    // position.
+    LiveRange* tail = SplitBetween(current,
+                                   current->Start(),
+                                   block_pos[reg].InstructionStart());
+    AddToUnhandledSorted(tail);
   }
+
+  // Register reg is not blocked for the whole range.
+  ASSERT(block_pos[reg].Value() >= current->End().Value());
+  TraceAlloc("Assigning reg %s to live range %d\n",
+             RegisterName(reg),
+             current->id());
+  current->set_assigned_register(reg, mode_);
+
+  // This register was not free. Thus we need to find and spill
+  // parts of active and inactive live regions that use the same register
+  // at the same lifetime positions as current.
+  SplitAndSpillIntersecting(current);
 }
 
 
@@ -1875,9 +1925,9 @@ void LAllocator::SplitAndSpillIntersecting(LiveRange* current) {
     if (range->assigned_register() == reg) {
       UsePosition* next_pos = range->NextRegisterPosition(current->Start());
       if (next_pos == NULL) {
-        SplitAndSpill(range, split_pos);
+        SpillAfter(range, split_pos);
       } else {
-        SplitAndSpill(range, split_pos, next_pos->pos());
+        SpillBetween(range, split_pos, next_pos->pos());
       }
       ActiveToHandled(range);
       --i;
@@ -1892,10 +1942,10 @@ void LAllocator::SplitAndSpillIntersecting(LiveRange* current) {
       if (next_intersection.IsValid()) {
         UsePosition* next_pos = range->NextRegisterPosition(current->Start());
         if (next_pos == NULL) {
-          SplitAndSpill(range, split_pos);
+          SpillAfter(range, split_pos);
         } else {
           next_intersection = Min(next_intersection, next_pos->pos());
-          SplitAndSpill(range, split_pos, next_intersection);
+          SpillBetween(range, split_pos, next_intersection);
         }
         InactiveToHandled(range);
         --i;
@@ -1905,19 +1955,50 @@ void LAllocator::SplitAndSpillIntersecting(LiveRange* current) {
 }
 
 
-LiveRange* LAllocator::Split(LiveRange* range,
-                             LifetimePosition start,
-                             LifetimePosition end) {
+bool LAllocator::IsBlockBoundary(LifetimePosition pos) {
+  return pos.IsInstructionStart() &&
+      chunk_->instructions()->at(pos.InstructionIndex())->IsLabel();
+}
+
+
+void LAllocator::AddGapMove(int pos, LiveRange* prev, LiveRange* next) {
+  UsePosition* prev_pos = prev->AddUsePosition(
+      LifetimePosition::FromInstructionIndex(pos));
+  UsePosition* next_pos = next->AddUsePosition(
+      LifetimePosition::FromInstructionIndex(pos));
+  LOperand* prev_operand = prev_pos->operand();
+  LOperand* next_operand = next_pos->operand();
+  LGap* gap = chunk_->GetGapAt(pos);
+  gap->GetOrCreateParallelMove(LGap::START)->
+      AddMove(prev_operand, next_operand);
+  next_pos->set_hint(prev_operand);
+}
+
+
+LiveRange* LAllocator::SplitAt(LiveRange* range, LifetimePosition pos) {
+  ASSERT(!range->IsFixed());
+  TraceAlloc("Splitting live range %d at %d\n", range->id(), pos.Value());
+
+  if (pos.Value() <= range->Start().Value()) return range;
+
+  LiveRange* result = LiveRangeFor(next_virtual_register_++);
+  range->SplitAt(pos, result);
+  return result;
+}
+
+
+LiveRange* LAllocator::SplitBetween(LiveRange* range,
+                                    LifetimePosition start,
+                                    LifetimePosition end) {
   ASSERT(!range->IsFixed());
-  TraceAlloc("Splitting live range %d in position between [%d, %d[\n",
+  TraceAlloc("Splitting live range %d in position between [%d, %d]\n",
              range->id(),
              start.Value(),
              end.Value());
 
-  LifetimePosition split_pos = FindOptimalSplitPos(
-      start, end.PrevInstruction().InstructionEnd());
+  LifetimePosition split_pos = FindOptimalSplitPos(start, end);
   ASSERT(split_pos.Value() >= start.Value());
-  return Split(range, split_pos);
+  return SplitAt(range, split_pos);
 }
 
 
@@ -1940,79 +2021,52 @@ LifetimePosition LAllocator::FindOptimalSplitPos(LifetimePosition start,
   }
 
   HBasicBlock* block = end_block;
-  // Move to the most outside loop header.
+  // Find header of outermost loop.
   while (block->parent_loop_header() != NULL &&
       block->parent_loop_header()->block_id() > start_block->block_id()) {
     block = block->parent_loop_header();
   }
 
-  if (block == end_block) {
-    return end;
-  }
+  if (block == end_block) return end;
 
   return LifetimePosition::FromInstructionIndex(
       block->first_instruction_index());
 }
 
 
-bool LAllocator::IsBlockBoundary(LifetimePosition pos) {
-  return pos.IsInstructionStart() &&
-      chunk_->instructions()->at(pos.InstructionIndex())->IsLabel();
+void LAllocator::SpillAfter(LiveRange* range, LifetimePosition pos) {
+  LiveRange* second_part = SplitAt(range, pos);
+  Spill(second_part);
 }
 
 
-void LAllocator::AddGapMove(int pos, LiveRange* prev, LiveRange* next) {
-  UsePosition* prev_pos = prev->AddUsePosition(
-      LifetimePosition::FromInstructionIndex(pos));
-  UsePosition* next_pos = next->AddUsePosition(
-      LifetimePosition::FromInstructionIndex(pos));
-  LOperand* prev_operand = prev_pos->operand();
-  LOperand* next_operand = next_pos->operand();
-  LGap* gap = chunk_->GetGapAt(pos);
-  gap->GetOrCreateParallelMove(LGap::START)->
-      AddMove(prev_operand, next_operand);
-  next_pos->set_hint(prev_operand);
-}
-
+void LAllocator::SpillBetween(LiveRange* range,
+                              LifetimePosition start,
+                              LifetimePosition end) {
+  ASSERT(start.Value() < end.Value());
+  LiveRange* second_part = SplitAt(range, start);
 
-LiveRange* LAllocator::Split(LiveRange* range, LifetimePosition pos) {
-  ASSERT(!range->IsFixed());
-  TraceAlloc("Splitting live range %d at %d\n", range->id(), pos.Value());
-  if (pos.Value() <= range->Start().Value()) {
-    return range;
-  }
-  LiveRange* result = LiveRangeFor(next_virtual_register_++);
-  range->SplitAt(pos, result);
-  return result;
-}
+  if (second_part->Start().Value() < end.Value()) {
+    // The split result intersects with [start, end[.
+    // Split it at position between ]start+1, end[, spill the middle part
+    // and put the rest to unhandled.
+    LiveRange* third_part = SplitBetween(
+        second_part,
+        second_part->Start().InstructionEnd(),
+        end.PrevInstruction().InstructionEnd());
 
+    ASSERT(third_part != second_part);
 
-void LAllocator::SplitAndSpill(LiveRange* range,
-                               LifetimePosition start,
-                               LifetimePosition end) {
-  // We have an interval range and want to make sure that it is
-  // spilled at start and at most spilled until end.
-  ASSERT(start.Value() < end.Value());
-  LiveRange* tail_part = Split(range, start);
-  if (tail_part->Start().Value() < end.Value()) {
-    LiveRange* third_part = Split(tail_part,
-                                  tail_part->Start().NextInstruction(),
-                                  end);
-    Spill(tail_part);
-    ASSERT(third_part != tail_part);
+    Spill(second_part);
     AddToUnhandledSorted(third_part);
   } else {
-    AddToUnhandledSorted(tail_part);
+    // The split result does not intersect with [start, end[.
+    // Nothing to spill. Just put it to unhandled as whole.
+    AddToUnhandledSorted(second_part);
   }
 }
 
 
-void LAllocator::SplitAndSpill(LiveRange* range, LifetimePosition at) {
-  LiveRange* second_part = Split(range, at);
-  Spill(second_part);
-}
-
-
 void LAllocator::Spill(LiveRange* range) {
   ASSERT(!range->IsSpilled());
   TraceAlloc("Spilling live range %d\n", range->id());
@@ -2020,7 +2074,7 @@ void LAllocator::Spill(LiveRange* range) {
 
   if (!first->HasAllocatedSpillOperand()) {
     LOperand* op = TryReuseSpillSlot(range);
-    if (op == NULL) op = chunk_->GetNextSpillSlot(mode_ == XMM_REGISTERS);
+    if (op == NULL) op = chunk_->GetNextSpillSlot(mode_ == DOUBLE_REGISTERS);
     first->SetSpillOperand(op);
   }
   range->MakeSpilled();

src/lithium-allocator.h

@@ -55,6 +55,7 @@ class LPointerMap;
 class LStackSlot;
 class LRegister;
 
+
 // This class represents a single point of a LOperand's lifetime.
 // For each lithium instruction there are exactly two lifetime positions:
 // the beginning and the end of the instruction. Lifetime positions for
@@ -121,7 +122,13 @@ class LifetimePosition {
   // instruction.
   bool IsValid() const { return value_ != -1; }
 
-  static LifetimePosition Invalid() { return LifetimePosition(); }
+  static inline LifetimePosition Invalid() { return LifetimePosition(); }
+
+  static inline LifetimePosition MaxPosition() {
+    // We have to use this kind of getter instead of static member due to
+    // crash bug in GDB.
+    return LifetimePosition(kMaxInt);
+  }
 
  private:
   static const int kStep = 2;
@@ -135,6 +142,13 @@ class LifetimePosition {
 };
 
 
+enum RegisterKind {
+  NONE,
+  GENERAL_REGISTERS,
+  DOUBLE_REGISTERS
+};
+
+
 class LOperand: public ZoneObject {
  public:
   enum Kind {
@@ -594,8 +608,8 @@ class LiveRange: public ZoneObject {
   explicit LiveRange(int id)
       : id_(id),
         spilled_(false),
-        assigned_double_(false),
         assigned_register_(kInvalidAssignment),
+        assigned_register_kind_(NONE),
         last_interval_(NULL),
         first_interval_(NULL),
         first_pos_(NULL),
@@ -620,10 +634,10 @@ class LiveRange: public ZoneObject {
   LOperand* CreateAssignedOperand();
   int assigned_register() const { return assigned_register_; }
   int spill_start_index() const { return spill_start_index_; }
-  void set_assigned_register(int reg, bool double_reg) {
+  void set_assigned_register(int reg, RegisterKind register_kind) {
     ASSERT(!HasRegisterAssigned() && !IsSpilled());
     assigned_register_ = reg;
-    assigned_double_ = double_reg;
+    assigned_register_kind_ = register_kind;
     ConvertOperands();
   }
   void MakeSpilled() {
@@ -652,9 +666,13 @@ class LiveRange: public ZoneObject {
   // Can this live range be spilled at this position.
   bool CanBeSpilled(LifetimePosition pos);
 
+  // Split this live range at the given position which must follow the start of
+  // the range.
+  // All uses following the given position will be moved from this
+  // live range to the result live range.
   void SplitAt(LifetimePosition position, LiveRange* result);
 
-  bool IsDouble() const { return assigned_double_; }
+  bool IsDouble() const { return assigned_register_kind_ == DOUBLE_REGISTERS; }
   bool HasRegisterAssigned() const {
     return assigned_register_ != kInvalidAssignment;
   }
@@ -721,8 +739,8 @@ class LiveRange: public ZoneObject {
 
   int id_;
   bool spilled_;
-  bool assigned_double_;
   int assigned_register_;
+  RegisterKind assigned_register_kind_;
   UseInterval* last_interval_;
   UseInterval* first_interval_;
   UsePosition* first_pos_;
@@ -774,8 +792,8 @@ class LAllocator BASE_EMBEDDED {
   // Checks whether the value of a given virtual register is tagged.
   bool HasTaggedValue(int virtual_register) const;
 
-  // Checks whether the value of a given virtual register is a double.
-  bool HasDoubleValue(int virtual_register) const;
+  // Returns the register kind required by the given virtual register.
+  RegisterKind RequiredRegisterKind(int virtual_register) const;
 
   // Begin a new instruction.
   void BeginInstruction();
@@ -814,12 +832,6 @@ class LAllocator BASE_EMBEDDED {
 #endif
 
  private:
-  enum OperationMode {
-    NONE,
-    CPU_REGISTERS,
-    XMM_REGISTERS
-  };
-
   void MeetRegisterConstraints();
   void ResolvePhis();
   void BuildLiveRanges();
@@ -871,17 +883,38 @@ class LAllocator BASE_EMBEDDED {
   // Helper methods for allocating registers.
   bool TryAllocateFreeReg(LiveRange* range);
   void AllocateBlockedReg(LiveRange* range);
-  void SplitAndSpillIntersecting(LiveRange* range);
+
+  // Live range splitting helpers.
+
+  // Split the given range at the given position.
+  // If range starts at or after the given position then the
+  // original range is returned.
+  // Otherwise returns the live range that starts at pos and contains
+  // all uses from the original range that follow pos. Uses at pos will
+  // still be owned by the original range after splitting.
+  LiveRange* SplitAt(LiveRange* range, LifetimePosition pos);
+
+  // Split the given range in a position from the interval [start, end].
+  LiveRange* SplitBetween(LiveRange* range,
+                          LifetimePosition start,
+                          LifetimePosition end);
+
+  // Find a lifetime position in the interval [start, end] which
+  // is optimal for splitting: it is either header of the outermost
+  // loop covered by this interval or the latest possible position.
   LifetimePosition FindOptimalSplitPos(LifetimePosition start,
                                        LifetimePosition end);
-  LiveRange* Split(LiveRange* range,
-                   LifetimePosition start,
-                   LifetimePosition end);
-  LiveRange* Split(LiveRange* range, LifetimePosition split_pos);
-  void SplitAndSpill(LiveRange* range,
-                     LifetimePosition start,
-                     LifetimePosition end);
-  void SplitAndSpill(LiveRange* range, LifetimePosition at);
+
+  // Spill the given life range after position pos.
+  void SpillAfter(LiveRange* range, LifetimePosition pos);
+
+  // Spill the given life range after position start and up to position end.
+  void SpillBetween(LiveRange* range,
+                    LifetimePosition start,
+                    LifetimePosition end);
+
+  void SplitAndSpillIntersecting(LiveRange* range);
+
   void Spill(LiveRange* range);
   bool IsBlockBoundary(LifetimePosition pos);
   void AddGapMove(int pos, LiveRange* prev, LiveRange* next);
@@ -914,6 +947,8 @@ class LAllocator BASE_EMBEDDED {
   HPhi* LookupPhi(LOperand* operand) const;
   LGap* GetLastGap(HBasicBlock* block) const;
 
+  const char* RegisterName(int allocation_index);
+
   LChunk* chunk_;
   ZoneList<InstructionSummary*> summaries_;
   InstructionSummary* next_summary_;
@@ -938,7 +973,7 @@ class LAllocator BASE_EMBEDDED {
   // Next virtual register number to be assigned to temporaries.
   int next_virtual_register_;
 
-  OperationMode mode_;
+  RegisterKind mode_;
   int num_registers_;
 
   HGraph* graph_;

test/mjsunit/regress/regress-962.js

+// Copyright 2010 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+function L(scope) { this.s = new Object(); }
+
+L.prototype.c = function() { return true; }
+
+function F() {
+  this.l = [new L, new L];
+}
+
+F.prototype.foo = function () {
+    var f, d = arguments,
+        e, b = this.l,
+        g;
+    for (e = 0; e < b.length; e++) {
+        g = b[e];
+        f = g.c.apply(g.s, d);
+        if (f === false) {
+            break
+        }
+    }
+    return f
+}
+
+
+var ctx = new F;
+
+for (var i = 0; i < 10000000; i++) ctx.foo();