[Turbofan] Re-enable single splinter.

Revert "Revert of [turbofan] Splinter into one range.
(patchset #2 id:80001 of https://codereview.chromium.org/1391023007/ )"

This reverts commit 23a8837f.

Also added a CHECK in Merge to validate that splitting yields a different
range and thus advances the algorithm. Ran stress bots successfully. Likely my earlier change in Splintering addressed the stress test scenario
that was looping infinitely.

BUG=

Review URL: https://codereview.chromium.org/1406983004

Cr-Commit-Position: refs/heads/master@{#31430}

src/compiler/js-native-context-specialization.cc

@@ -608,7 +608,7 @@ Reduction JSNativeContextSpecialization::ReduceJSLoadNamed(Node* node) {
 // jump). Generating a single Merge here, which joins all the deoptimizing
 // controls would generate a lot of these basic blocks, however. So this
 // is disabled for now until splintering is fixed.
-#if 0
+#if 1
   // Generate the single "exit" point, where we get if either all map/instance
   // type checks failed, or one of the assumptions inside one of the cases
   // failes (i.e. failing prototype chain check).

src/compiler/live-range-separator.cc

@@ -44,12 +44,14 @@ void CreateSplinter(TopLevelLiveRange *range, RegisterAllocationData *data,
     if (range->MayRequireSpillRange()) {
       data->CreateSpillRangeForLiveRange(range);
     }
-    TopLevelLiveRange *result = data->NextLiveRange(range->machine_type());
-    DCHECK_NULL(data->live_ranges()[result->vreg()]);
-    data->live_ranges()[result->vreg()] = result;
-
+    if (range->splinter() == nullptr) {
+      TopLevelLiveRange *splinter = data->NextLiveRange(range->machine_type());
+      DCHECK_NULL(data->live_ranges()[splinter->vreg()]);
+      data->live_ranges()[splinter->vreg()] = splinter;
+      range->SetSplinter(splinter);
+    }
     Zone *zone = data->allocation_zone();
-    range->Splinter(start, end, result, zone);
+    range->Splinter(start, end, zone);
   }
 }
 

src/compiler/register-allocator.cc

@@ -698,7 +698,8 @@ TopLevelLiveRange::TopLevelLiveRange(int vreg, MachineType machine_type)
       spilled_in_deferred_blocks_(false),
       spill_start_index_(kMaxInt),
       last_child_(this),
-      last_insertion_point_(this) {
+      last_pos_(nullptr),
+      splinter_(nullptr) {
   bits_ |= SpillTypeField::encode(SpillType::kNoSpillType);
 }
 
@@ -845,12 +846,12 @@ AllocatedOperand TopLevelLiveRange::GetSpillRangeOperand() const {
 
 
 void TopLevelLiveRange::Splinter(LifetimePosition start, LifetimePosition end,
-                                 TopLevelLiveRange* result, Zone* zone) {
+                                 Zone* zone) {
   DCHECK(start != Start() || end != End());
   DCHECK(start < end);
 
-  result->set_spill_type(spill_type());
-
+  TopLevelLiveRange splinter_temp(-1, machine_type());
+  UsePosition* last_in_splinter = nullptr;
   if (start <= Start()) {
     // TODO(mtrofin): here, the TopLevel part is in the deferred range, so we
     // may want to continue processing the splinter. However, if the value is
@@ -859,21 +860,21 @@ void TopLevelLiveRange::Splinter(LifetimePosition start, LifetimePosition end,
     // should check this, however, this may not be the place, because we don't
     // have access to the instruction sequence.
     DCHECK(end < End());
-    DetachAt(end, result, zone);
+    DetachAt(end, &splinter_temp, zone);
     next_ = nullptr;
   } else if (end >= End()) {
     DCHECK(start > Start());
-    DetachAt(start, result, zone);
+    DetachAt(start, &splinter_temp, zone);
     next_ = nullptr;
   } else {
     DCHECK(start < End() && Start() < end);
 
     const int kInvalidId = std::numeric_limits<int>::max();
 
-    UsePosition* last = DetachAt(start, result, zone);
+    UsePosition* last = DetachAt(start, &splinter_temp, zone);
 
     LiveRange end_part(kInvalidId, this->machine_type(), nullptr);
-    result->DetachAt(end, &end_part, zone);
+    last_in_splinter = splinter_temp.DetachAt(end, &end_part, zone);
 
     next_ = end_part.next_;
     last_interval_->set_next(end_part.first_interval_);
@@ -890,20 +891,39 @@ void TopLevelLiveRange::Splinter(LifetimePosition start, LifetimePosition end,
       if (last != nullptr) last->set_next(end_part.first_pos_);
     }
   }
-  result->next_ = nullptr;
-  result->top_level_ = result;
 
-  result->SetSplinteredFrom(this);
-  // Ensure the result's relative ID is unique within the IDs used for this
-  // virtual register's children and splinters.
-  result->relative_id_ = GetNextChildId();
+  if (splinter()->IsEmpty()) {
+    splinter()->first_interval_ = splinter_temp.first_interval_;
+    splinter()->last_interval_ = splinter_temp.last_interval_;
+  } else {
+    splinter()->last_interval_->set_next(splinter_temp.first_interval_);
+    splinter()->last_interval_ = splinter_temp.last_interval_;
+  }
+  if (splinter()->first_pos() == nullptr) {
+    splinter()->first_pos_ = splinter_temp.first_pos_;
+  } else {
+    splinter()->last_pos_->set_next(splinter_temp.first_pos_);
+  }
+  if (last_in_splinter != nullptr) {
+    splinter()->last_pos_ = last_in_splinter;
+  } else {
+    if (splinter()->first_pos() != nullptr &&
+        splinter()->last_pos_ == nullptr) {
+      splinter()->last_pos_ = splinter()->first_pos();
+      for (UsePosition* pos = splinter()->first_pos(); pos != nullptr;
+           pos = pos->next()) {
+        splinter()->last_pos_ = pos;
+      }
+    }
+  }
+#if DEBUG
+  Verify();
+  splinter()->Verify();
+#endif
 }
 
 
 void TopLevelLiveRange::SetSplinteredFrom(TopLevelLiveRange* splinter_parent) {
-  // The splinter parent is always the original "Top".
-  DCHECK(splinter_parent->Start() < Start());
-
   splintered_from_ = splinter_parent;
   if (!HasSpillOperand() && splinter_parent->spill_range_ != nullptr) {
     SetSpillRange(splinter_parent->spill_range_);
@@ -928,43 +948,55 @@ void TopLevelLiveRange::Merge(TopLevelLiveRange* other, Zone* zone) {
   DCHECK(Start() < other->Start());
   DCHECK(other->splintered_from() == this);
 
-  LiveRange* last_other = other->last_child();
-  LiveRange* last_me = last_child();
-
-  // Simple case: we just append at the end.
-  if (last_me->End() <= other->Start()) return last_me->AppendAsChild(other);
-
-  DCHECK(last_me->End() > last_other->End());
+  LiveRange* first = this;
+  LiveRange* second = other;
+  DCHECK(first->Start() < second->Start());
+  while (first != nullptr && second != nullptr) {
+    DCHECK(first != second);
+    // Make sure the ranges are in order each time we iterate.
+    if (second->Start() < first->Start()) {
+      LiveRange* tmp = second;
+      second = first;
+      first = tmp;
+      continue;
+    }
 
-  // In the more general case, we need to find the ranges between which to
-  // insert.
-  if (other->Start() < last_insertion_point_->Start()) {
-    last_insertion_point_ = this;
-  }
+    if (first->End() <= second->Start()) {
+      if (first->next() == nullptr ||
+          first->next()->Start() > second->Start()) {
+        // First is in order before second.
+        LiveRange* temp = first->next();
+        first->next_ = second;
+        first = temp;
+      } else {
+        // First is in order before its successor (or second), so advance first.
+        first = first->next();
+      }
+      continue;
+    }
 
-  for (; last_insertion_point_->next() != nullptr &&
-         last_insertion_point_->next()->Start() <= other->Start();
-       last_insertion_point_ = last_insertion_point_->next()) {
-  }
+    DCHECK(first->Start() < second->Start());
+    // If first and second intersect, split first.
+    if (first->Start() < second->End() && second->Start() < first->End()) {
+      LiveRange* temp = first->SplitAt(second->Start(), zone);
+      CHECK(temp != first);
+      temp->set_spilled(first->spilled());
+      if (!temp->spilled())
+        temp->set_assigned_register(first->assigned_register());
 
-  // When we splintered the original range, we reconstituted the original range
-  // into one range without children, but with discontinuities. To merge the
-  // splinter back in, we need to split the range - or a child obtained after
-  // register allocation splitting.
-  LiveRange* after = last_insertion_point_->next();
-  if (last_insertion_point_->End() > other->Start()) {
-    LiveRange* new_after = last_insertion_point_->SplitAt(other->Start(), zone);
-    new_after->set_spilled(last_insertion_point_->spilled());
-    if (!new_after->spilled())
-      new_after->set_assigned_register(
-          last_insertion_point_->assigned_register());
-    after = new_after;
+      first->next_ = second;
+      first = temp;
+      continue;
+    }
+    DCHECK(first->End() <= second->Start());
   }
 
-  last_other->next_ = after;
-  last_insertion_point_->next_ = other;
-  other->UpdateParentForAllChildren(TopLevel());
+  TopLevel()->UpdateParentForAllChildren(TopLevel());
   TopLevel()->UpdateSpillRangePostMerge(other);
+
+#if DEBUG
+  Verify();
+#endif
 }
 
 

src/compiler/register-allocator.h

@@ -495,8 +495,7 @@ class TopLevelLiveRange final : public LiveRange {
   // result.
   // The current range is pointed to as "splintered_from". No parent/child
   // relationship is established between this and result.
-  void Splinter(LifetimePosition start, LifetimePosition end,
-                TopLevelLiveRange* result, Zone* zone);
+  void Splinter(LifetimePosition start, LifetimePosition end, Zone* zone);
 
   // Assuming other was splintered from this range, embeds other and its
   // children as part of the children sequence of this range.
@@ -540,7 +539,6 @@ class TopLevelLiveRange final : public LiveRange {
     spill_start_index_ = Min(start, spill_start_index_);
   }
 
-  void SetSplinteredFrom(TopLevelLiveRange* splinter_parent);
   void CommitSpillsAtDefinition(InstructionSequence* sequence,
                                 const InstructionOperand& operand,
                                 bool might_be_duplicated);
@@ -580,8 +578,20 @@ class TopLevelLiveRange final : public LiveRange {
   }
   void set_last_child(LiveRange* range) { last_child_ = range; }
   LiveRange* last_child() const { return last_child_; }
+  TopLevelLiveRange* splinter() const { return splinter_; }
+  void SetSplinter(TopLevelLiveRange* splinter) {
+    DCHECK_NULL(splinter_);
+    DCHECK_NOT_NULL(splinter);
+
+    splinter_ = splinter;
+    splinter->relative_id_ = GetNextChildId();
+    splinter->set_spill_type(spill_type());
+    splinter->SetSplinteredFrom(this);
+  }
 
  private:
+  void SetSplinteredFrom(TopLevelLiveRange* splinter_parent);
+
   typedef BitField<bool, 1, 1> HasSlotUseField;
   typedef BitField<bool, 2, 1> IsPhiField;
   typedef BitField<bool, 3, 1> IsNonLoopPhiField;
@@ -601,7 +611,8 @@ class TopLevelLiveRange final : public LiveRange {
   bool spilled_in_deferred_blocks_;
   int spill_start_index_;
   LiveRange* last_child_;
-  LiveRange* last_insertion_point_;
+  UsePosition* last_pos_;
+  TopLevelLiveRange* splinter_;
 
   DISALLOW_COPY_AND_ASSIGN(TopLevelLiveRange);
 };

test/unittests/compiler/live-range-unittest.cc

@@ -32,11 +32,14 @@ class LiveRangeUnitTest : public TestWithZone {
 
   TopLevelLiveRange* Splinter(TopLevelLiveRange* top, int start, int end,
                               int new_id = 0) {
-    TopLevelLiveRange* ret =
-        new (zone()) TopLevelLiveRange(new_id, MachineType::kRepTagged);
+    if (top->splinter() == nullptr) {
+      TopLevelLiveRange* ret =
+          new (zone()) TopLevelLiveRange(new_id, MachineType::kRepTagged);
+      top->SetSplinter(ret);
+    }
     top->Splinter(LifetimePosition::FromInt(start),
-                  LifetimePosition::FromInt(end), ret, zone());
-    return ret;
+                  LifetimePosition::FromInt(end), zone());
+    return top->splinter();
   }
 
   // Ranges first and second match structurally.
@@ -377,6 +380,25 @@ TEST_F(LiveRangeUnitTest, SplinterMultipleIntervalsRight) {
 }
 
 
+TEST_F(LiveRangeUnitTest, SplinterMergeMultipleTimes) {
+  TopLevelLiveRange* range =
+      TestRangeBuilder(zone()).Add(0, 3).Add(5, 10).Add(12, 16).Build();
+  Splinter(range, 4, 6);
+  Splinter(range, 8, 14);
+  TopLevelLiveRange* splinter = range->splinter();
+  EXPECT_EQ(nullptr, range->next());
+  EXPECT_EQ(nullptr, splinter->next());
+  EXPECT_EQ(range, splinter->splintered_from());
+
+  TopLevelLiveRange* expected_source =
+      TestRangeBuilder(zone()).Add(0, 3).Add(6, 8).Add(14, 16).Build();
+  TopLevelLiveRange* expected_splinter =
+      TestRangeBuilder(zone()).Add(5, 6).Add(8, 10).Add(12, 14).Build();
+  EXPECT_TRUE(RangesMatch(expected_source, range));
+  EXPECT_TRUE(RangesMatch(expected_splinter, splinter));
+}
+
+
 TEST_F(LiveRangeUnitTest, MergeMultipleIntervalsRight) {
   TopLevelLiveRange* original =
       TestRangeBuilder(zone()).Add(0, 3).Add(5, 8).Build();
@@ -416,8 +438,9 @@ TEST_F(LiveRangeUnitTest, IDGeneration) {
 
   TopLevelLiveRange* splinter =
       new (zone()) TopLevelLiveRange(101, MachineType::kRepTagged);
+  vreg->SetSplinter(splinter);
   vreg->Splinter(LifetimePosition::FromInt(4), LifetimePosition::FromInt(12),
-                 splinter, zone());
+                 zone());
 
   EXPECT_EQ(101, splinter->vreg());
   EXPECT_EQ(1, splinter->relative_id());