Revert "[regalloc] Use an adaptive data structure for live sets"

This reverts commit b3d748a2.

Reason for revert: Regressions, see https://crbug.com/1023423.

Original change's description:
> [regalloc] Use an adaptive data structure for live sets
> 
> Live sets represent sets of live virtual registers at block entry and
> exit points. They are usually sparsely populated; for example, a sample
> taken from Octane2 shows 80% of sampled live sets with a fill ratio of
> 10% or less.
> 
> Prior to this CL, live sets were implemented as a statically-sized bit
> vector. This is fine for low-ish virtual register counts, but becomes
> wasteful at higher numbers.
> 
> This CL attempts to address this issue through an adaptive
> implementation. Small live sets remain bit vectors, while larger sets
> switch to a PersistentMap-based implementation. PersistentMap has very
> memory-efficient add/remove/copy operations.
> 
> Of course, with adaptive data structures we enter the territory of
> parameter fiddling. In this case, two parameters are used:
> kMaxSmallSetSize controls when to switch implementations, and
> kMaxDeletionsBeforePrune controls when pruning (= managing the # of
> deleted entries in the map) sets in.
> 
> On the (degenerate) test case from the linked bug, the register
> allocation zone shrinks from 1008MB to 475MB. For more realistic cases
> I expect savings on the order of 10s of KB.
> 
> Bug: v8:9574
> Change-Id: Id903bbe23f030b418e8d887ef4839c8d65126c52
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1891693
> Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
> Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64872}

TBR=jgruber@chromium.org,tebbi@chromium.org,thibaudm@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:9574
Change-Id: I5d684198f9c4575a0c892076459cc2c20dce9aec
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1910944Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64912}

src/compiler/backend/register-allocator.h

@@ -21,8 +21,6 @@ class TickCounter;
 
 namespace compiler {
 
-class LiveSet;
-
 static const int32_t kUnassignedRegister = RegisterConfiguration::kMaxRegisters;
 
 enum RegisterKind { GENERAL_REGISTERS, FP_REGISTERS };
@@ -279,8 +277,8 @@ class RegisterAllocationData final : public ZoneObject {
   const ZoneVector<TopLevelLiveRange*>& fixed_simd128_live_ranges() const {
     return fixed_simd128_live_ranges_;
   }
-  ZoneVector<LiveSet*>& live_in_sets() { return live_in_sets_; }
-  ZoneVector<LiveSet*>& live_out_sets() { return live_out_sets_; }
+  ZoneVector<BitVector*>& live_in_sets() { return live_in_sets_; }
+  ZoneVector<BitVector*>& live_out_sets() { return live_out_sets_; }
   ZoneVector<SpillRange*>& spill_ranges() { return spill_ranges_; }
   DelayedReferences& delayed_references() { return delayed_references_; }
   InstructionSequence* code() const { return code_; }
@@ -354,8 +352,8 @@ class RegisterAllocationData final : public ZoneObject {
   const char* const debug_name_;
   const RegisterConfiguration* const config_;
   PhiMap phi_map_;
-  ZoneVector<LiveSet*> live_in_sets_;
-  ZoneVector<LiveSet*> live_out_sets_;
+  ZoneVector<BitVector*> live_in_sets_;
+  ZoneVector<BitVector*> live_out_sets_;
   ZoneVector<TopLevelLiveRange*> live_ranges_;
   ZoneVector<TopLevelLiveRange*> fixed_live_ranges_;
   ZoneVector<TopLevelLiveRange*> fixed_float_live_ranges_;
@@ -1105,8 +1103,8 @@ class LiveRangeBuilder final : public ZoneObject {
 
   // Phase 3: compute liveness of all virtual register.
   void BuildLiveRanges();
-  static LiveSet* ComputeLiveOut(const InstructionBlock* block,
-                                 RegisterAllocationData* data);
+  static BitVector* ComputeLiveOut(const InstructionBlock* block,
+                                   RegisterAllocationData* data);
 
  private:
   using SpillMode = RegisterAllocationData::SpillMode;
@@ -1118,7 +1116,9 @@ class LiveRangeBuilder final : public ZoneObject {
   Zone* allocation_zone() const { return data()->allocation_zone(); }
   Zone* code_zone() const { return code()->zone(); }
   const RegisterConfiguration* config() const { return data()->config(); }
-  ZoneVector<LiveSet*>& live_in_sets() const { return data()->live_in_sets(); }
+  ZoneVector<BitVector*>& live_in_sets() const {
+    return data()->live_in_sets();
+  }
 
   // Verification.
   void Verify() const;
@@ -1128,10 +1128,10 @@ class LiveRangeBuilder final : public ZoneObject {
   bool NextIntervalStartsInDifferentBlocks(const UseInterval* interval) const;
 
   // Liveness analysis support.
-  void AddInitialIntervals(const InstructionBlock* block, LiveSet* live_out);
-  void ProcessInstructions(const InstructionBlock* block, LiveSet* live);
-  void ProcessPhis(const InstructionBlock* block, LiveSet* live);
-  void ProcessLoopHeader(const InstructionBlock* block, LiveSet* live);
+  void AddInitialIntervals(const InstructionBlock* block, BitVector* live_out);
+  void ProcessInstructions(const InstructionBlock* block, BitVector* live);
+  void ProcessPhis(const InstructionBlock* block, BitVector* live);
+  void ProcessLoopHeader(const InstructionBlock* block, BitVector* live);
 
   static int FixedLiveRangeID(int index) { return -index - 1; }
   int FixedFPLiveRangeID(int index, MachineRepresentation rep);

src/compiler/persistent-map.h

@@ -88,8 +88,6 @@ class PersistentMap {
     return !(*this == other);
   }
 
-  Zone* zone() const { return zone_; }
-
   // The iterator produces key-value pairs in the lexicographical order of
   // hash value and key. It produces exactly the key-value pairs where the value
   // is not the default value.