Reland: Introducing the LLVM greedy register allocator.

This change aims to introduce the separation of the RegisterAllocator model, using the initial prototype for GreedyAllocator as proof of concept.

Summary:
- new flag, turbo-greedy-regalloc, enabling the new allocator. Default
  false.
- initial, untested implementation for the GreedyAllocator.

BUG=

Review URL: https://codereview.chromium.org/1061923005

Cr-Commit-Position: refs/heads/master@{#28018}

src/compiler/pipeline.cc

@@ -742,23 +742,25 @@ struct BuildLiveRangesPhase {
 };
 
 
+template <typename RegAllocator>
 struct AllocateGeneralRegistersPhase {
   static const char* phase_name() { return "allocate general registers"; }
 
   void Run(PipelineData* data, Zone* temp_zone) {
-    LinearScanAllocator allocator(data->register_allocation_data(),
-                                  GENERAL_REGISTERS, temp_zone);
+    RegAllocator allocator(data->register_allocation_data(), GENERAL_REGISTERS,
+                           temp_zone);
     allocator.AllocateRegisters();
   }
 };
 
 
+template <typename RegAllocator>
 struct AllocateDoubleRegistersPhase {
   static const char* phase_name() { return "allocate double registers"; }
 
   void Run(PipelineData* data, Zone* temp_zone) {
-    LinearScanAllocator allocator(data->register_allocation_data(),
-                                  DOUBLE_REGISTERS, temp_zone);
+    RegAllocator allocator(data->register_allocation_data(), DOUBLE_REGISTERS,
+                           temp_zone);
     allocator.AllocateRegisters();
   }
 };
@@ -1269,8 +1271,13 @@ void Pipeline::AllocateRegisters(const RegisterConfiguration* config,
   if (verifier != nullptr) {
     CHECK(!data->register_allocation_data()->ExistsUseWithoutDefinition());
   }
-  Run<AllocateGeneralRegistersPhase>();
-  Run<AllocateDoubleRegistersPhase>();
+  if (FLAG_turbo_greedy_regalloc) {
+    Run<AllocateGeneralRegistersPhase<GreedyAllocator>>();
+    Run<AllocateDoubleRegistersPhase<GreedyAllocator>>();
+  } else {
+    Run<AllocateGeneralRegistersPhase<LinearScanAllocator>>();
+    Run<AllocateDoubleRegistersPhase<LinearScanAllocator>>();
+  }
   Run<AssignSpillSlotsPhase>();
 
   Run<CommitAssignmentPhase>();

src/compiler/register-allocator.h

@@ -585,11 +585,14 @@ class LiveRangeBuilder final : public ZoneObject {
 
 class RegisterAllocator : public ZoneObject {
  public:
-  explicit RegisterAllocator(RegisterAllocationData* data);
+  explicit RegisterAllocator(RegisterAllocationData* data, RegisterKind kind);
 
  protected:
   RegisterAllocationData* data() const { return data_; }
   InstructionSequence* code() const { return data()->code(); }
+  RegisterKind mode() const { return mode_; }
+  int num_registers() const { return num_registers_; }
+
   Zone* allocation_zone() const { return data()->allocation_zone(); }
 
   LiveRange* LiveRangeFor(int index) { return data()->LiveRangeFor(index); }
@@ -621,6 +624,8 @@ class RegisterAllocator : public ZoneObject {
 
  private:
   RegisterAllocationData* const data_;
+  const RegisterKind mode_;
+  const int num_registers_;
 
   DISALLOW_COPY_AND_ASSIGN(RegisterAllocator);
 };
@@ -635,7 +640,6 @@ class LinearScanAllocator final : public RegisterAllocator {
   void AllocateRegisters();
 
  private:
-  int num_registers() const { return num_registers_; }
   const char* RegisterName(int allocation_index) const;
 
   ZoneVector<LiveRange*>& unhandled_live_ranges() {
@@ -677,9 +681,6 @@ class LinearScanAllocator final : public RegisterAllocator {
 
   void SplitAndSpillIntersecting(LiveRange* range);
 
-  const RegisterKind mode_;
-  const int num_registers_;
-
   ZoneVector<LiveRange*> unhandled_live_ranges_;
   ZoneVector<LiveRange*> active_live_ranges_;
   ZoneVector<LiveRange*> inactive_live_ranges_;
@@ -691,6 +692,46 @@ class LinearScanAllocator final : public RegisterAllocator {
   DISALLOW_COPY_AND_ASSIGN(LinearScanAllocator);
 };
 
+class CoallescedLiveRanges;
+
+
+// A variant of the LLVM Greedy Register Allocator. See
+// http://blog.llvm.org/2011/09/greedy-register-allocation-in-llvm-30.html
+class GreedyAllocator final : public RegisterAllocator {
+ public:
+  explicit GreedyAllocator(RegisterAllocationData* data, RegisterKind kind,
+                           Zone* local_zone);
+
+  void AllocateRegisters();
+
+ private:
+  const RegisterConfiguration* config() const { return data()->config(); }
+
+  typedef ZonePriorityQueue<std::pair<unsigned, LiveRange*>> PQueue;
+
+  unsigned GetLiveRangeSize(LiveRange* range);
+  void Enqueue(LiveRange* range);
+
+  void Evict(LiveRange* range);
+  float CalculateSpillWeight(LiveRange* range);
+  float CalculateMaxSpillWeight(const ZoneSet<LiveRange*>& ranges);
+
+
+  bool TryAllocate(LiveRange* current, ZoneSet<LiveRange*>* conflicting);
+  bool TryAllocatePhysicalRegister(unsigned reg_id, LiveRange* range,
+                                   ZoneSet<LiveRange*>* conflicting);
+  bool HandleSpillOperands(LiveRange* range);
+  bool AllocateBlockedRange(LiveRange*, const ZoneSet<LiveRange*>&);
+
+  LiveRange* SpillBetweenUntil(LiveRange* range, LifetimePosition start,
+                               LifetimePosition until, LifetimePosition end);
+  void AssignRangeToRegister(int reg_id, LiveRange* range);
+
+  ZoneVector<CoallescedLiveRanges*> allocations_;
+  PQueue queue_;
+  DISALLOW_COPY_AND_ASSIGN(GreedyAllocator);
+};
+
 
 class OperandAssigner final : public ZoneObject {
  public:

src/flag-definitions.h

@@ -382,6 +382,7 @@ DEFINE_BOOL(omit_map_checks_for_leaf_maps, true,
 
 // Flags for TurboFan.
 DEFINE_BOOL(turbo, false, "enable TurboFan compiler")
+DEFINE_BOOL(turbo_greedy_regalloc, false, "use the greedy register allocator")
 DEFINE_IMPLICATION(turbo, turbo_deoptimization)
 DEFINE_IMPLICATION(turbo, turbo_type_feedback)
 DEFINE_STRING(turbo_filter, "~~", "optimization filter for TurboFan compiler")

src/zone-containers.h

@@ -63,6 +63,17 @@ class ZoneLinkedList : public std::list<T, zone_allocator<T>> {
 };
 
 
+// A wrapper subclass std::priority_queue to make it easy to construct one
+// that uses a zone allocator.
+template <typename T, typename Compare = std::less<T>>
+class ZonePriorityQueue : public std::priority_queue<T, ZoneVector<T>> {
+ public:
+  // Constructs an empty list.
+  explicit ZonePriorityQueue(Zone* zone)
+      : std::priority_queue<T, ZoneVector<T>>(Compare(), ZoneVector<T>(zone)) {}
+};
+
+
 // A wrapper subclass for std::queue to make it easy to construct one
 // that uses a zone allocator.
 template <typename T>