[turbofan] More thorough validation of LiveRanges.

Added structural validation to live ranges, esp. for bugs that may
arise due to splintering / merging.

BUG=

Review URL: https://codereview.chromium.org/1533723002

Cr-Commit-Position: refs/heads/master@{#32954}

src/compiler/register-allocator.cc

@@ -278,7 +278,7 @@ LiveRange::LiveRange(int relative_id, MachineRepresentation rep,
 }
 
 
-void LiveRange::Verify() const {
+void LiveRange::VerifyPositions() const {
   // Walk the positions, verifying that each is in an interval.
   auto interval = first_interval_;
   for (auto pos = first_pos_; pos != nullptr; pos = pos->next()) {
@@ -293,6 +293,18 @@ void LiveRange::Verify() const {
 }
 
 
+void LiveRange::VerifyIntervals() const {
+  DCHECK(first_interval()->start() == Start());
+  LifetimePosition last_end = first_interval()->end();
+  for (UseInterval* interval = first_interval()->next(); interval != nullptr;
+       interval = interval->next()) {
+    DCHECK(last_end <= interval->start());
+    last_end = interval->end();
+  }
+  DCHECK(last_end == End());
+}
+
+
 void LiveRange::set_assigned_register(int reg) {
   DCHECK(!HasRegisterAssigned() && !spilled());
   bits_ = AssignedRegisterField::update(bits_, reg);
@@ -530,8 +542,8 @@ UsePosition* LiveRange::DetachAt(LifetimePosition position, LiveRange* result,
   size_ = kInvalidSize;
   weight_ = kInvalidWeight;
 #ifdef DEBUG
-  Verify();
-  result->Verify();
+  VerifyChildStructure();
+  result->VerifyChildStructure();
 #endif
   return use_before;
 }
@@ -959,6 +971,24 @@ void TopLevelLiveRange::Merge(TopLevelLiveRange* other, Zone* zone) {
 }
 
 
+void TopLevelLiveRange::VerifyChildrenInOrder() const {
+  LifetimePosition last_end = End();
+  for (const LiveRange* child = this->next(); child != nullptr;
+       child = child->next()) {
+    DCHECK(last_end <= child->Start());
+    last_end = child->End();
+  }
+}
+
+
+void TopLevelLiveRange::Verify() const {
+  VerifyChildrenInOrder();
+  for (const LiveRange* child = this; child != nullptr; child = child->next()) {
+    VerifyChildStructure();
+  }
+}
+
+
 void TopLevelLiveRange::ShortenTo(LifetimePosition start) {
   TRACE("Shorten live range %d to [%d\n", vreg(), start.value());
   DCHECK(first_interval_ != nullptr);
@@ -2153,8 +2183,8 @@ void LiveRangeBuilder::Verify() const {
   for (auto& hint : phi_hints_) {
     CHECK(hint.second->IsResolved());
   }
-  for (LiveRange* current : data()->live_ranges()) {
-    if (current != nullptr) current->Verify();
+  for (TopLevelLiveRange* current : data()->live_ranges()) {
+    if (current != nullptr && !current->IsEmpty()) current->Verify();
   }
 }
 

src/compiler/register-allocator.h

@@ -398,7 +398,10 @@ class LiveRange : public ZoneObject {
   bool Covers(LifetimePosition position) const;
   LifetimePosition FirstIntersection(LiveRange* other) const;
 
-  void Verify() const;
+  void VerifyChildStructure() const {
+    VerifyIntervals();
+    VerifyPositions();
+  }
 
   void ConvertUsesToOperand(const InstructionOperand& op,
                             const InstructionOperand& spill_op);
@@ -431,6 +434,9 @@ class LiveRange : public ZoneObject {
   void AdvanceLastProcessedMarker(UseInterval* to_start_of,
                                   LifetimePosition but_not_past) const;
 
+  void VerifyPositions() const;
+  void VerifyIntervals() const;
+
   typedef BitField<bool, 0, 1> SpilledField;
   typedef BitField<int32_t, 6, 6> AssignedRegisterField;
   typedef BitField<MachineRepresentation, 12, 8> RepresentationField;
@@ -593,6 +599,9 @@ class TopLevelLiveRange final : public LiveRange {
   int debug_virt_reg() const;
 #endif
 
+  void Verify() const;
+  void VerifyChildrenInOrder() const;
+
   int GetNextChildId() {
     return IsSplinter() ? splintered_from()->GetNextChildId()
                         : ++last_child_id_;