[bitvector] Allow BitVector to resize

Allows BitVector to resize, updating its own data and data length to
match the new length. We can fast-path resizes which fit into the same
data length (since high bits are already zero), and replace the pattern
where a BitVector is cloned using CopyFrom.

Change-Id: If79ca782c516e93b2a27c5e335e263554d522e88
Reviewed-on: https://chromium-review.googlesource.com/539522
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46101}

src/bit-vector.h

@@ -83,13 +83,22 @@ class BitVector : public ZoneObject {
   }
 
   void CopyFrom(const BitVector& other) {
-    DCHECK(other.length() <= length());
-    for (int i = 0; i < other.data_length_; i++) {
-      data_[i] = other.data_[i];
-    }
-    for (int i = other.data_length_; i < data_length_; i++) {
-      data_[i] = 0;
+    DCHECK_LE(other.length(), length());
+    CopyFrom(other.data_, other.data_length_);
+  }
+
+  void Resize(int new_length, Zone* zone) {
+    DCHECK_GT(new_length, length());
+    int new_data_length = SizeFor(new_length);
+    if (new_data_length > data_length_) {
+      uintptr_t* old_data = data_;
+      int old_data_length = data_length_;
+
+      data_ = zone->NewArray<uintptr_t>(new_data_length);
+      data_length_ = new_data_length;
+      CopyFrom(old_data, old_data_length);
     }
+    length_ = new_length;
   }
 
   bool Contains(int i) const {
@@ -182,9 +191,19 @@ class BitVector : public ZoneObject {
 #endif
 
  private:
-  const int length_;
-  const int data_length_;
-  uintptr_t* const data_;
+  int length_;
+  int data_length_;
+  uintptr_t* data_;
+
+  void CopyFrom(uintptr_t* other_data, int other_data_length) {
+    DCHECK_LE(other_data_length, data_length_);
+    for (int i = 0; i < other_data_length; i++) {
+      data_[i] = other_data[i];
+    }
+    for (int i = other_data_length; i < data_length_; i++) {
+      data_[i] = 0;
+    }
+  }
 
   DISALLOW_COPY_AND_ASSIGN(BitVector);
 };
@@ -195,8 +214,8 @@ class GrowableBitVector BASE_EMBEDDED {
   class Iterator BASE_EMBEDDED {
    public:
     Iterator(const GrowableBitVector* target, Zone* zone)
-        : it_(target->bits_ == NULL ? new (zone) BitVector(1, zone)
-                                    : target->bits_) {}
+        : it_(target->bits_ == nullptr ? new (zone) BitVector(1, zone)
+                                       : target->bits_) {}
     bool Done() const { return it_.Done(); }
     void Advance() { it_.Advance(); }
     int Current() const { return it_.Current(); }
@@ -205,7 +224,7 @@ class GrowableBitVector BASE_EMBEDDED {
     BitVector::Iterator it_;
   };
 
-  GrowableBitVector() : bits_(NULL) {}
+  GrowableBitVector() : bits_(nullptr) {}
   GrowableBitVector(int length, Zone* zone)
       : bits_(new (zone) BitVector(length, zone)) {}
 
@@ -226,23 +245,26 @@ class GrowableBitVector BASE_EMBEDDED {
   }
 
   void Clear() {
-    if (bits_ != NULL) bits_->Clear();
+    if (bits_ != nullptr) bits_->Clear();
   }
 
  private:
   static const int kInitialLength = 1024;
 
   bool InBitsRange(int value) const {
-    return bits_ != NULL && bits_->length() > value;
+    return bits_ != nullptr && bits_->length() > value;
   }
 
   void EnsureCapacity(int value, Zone* zone) {
     if (InBitsRange(value)) return;
-    int new_length = bits_ == NULL ? kInitialLength : bits_->length();
+    int new_length = bits_ == nullptr ? kInitialLength : bits_->length();
     while (new_length <= value) new_length *= 2;
-    BitVector* new_bits = new (zone) BitVector(new_length, zone);
-    if (bits_ != NULL) new_bits->CopyFrom(*bits_);
-    bits_ = new_bits;
+
+    if (bits_ == nullptr) {
+      bits_ = new (zone) BitVector(new_length, zone);
+    } else {
+      bits_->Resize(new_length, zone);
+    }
   }
 
   BitVector* bits_;

src/compiler/scheduler.cc

@@ -940,10 +940,8 @@ class SpecialRPONumberer : public ZoneObject {
                        size_t num_loops, ZoneVector<Backedge>* backedges) {
     // Extend existing loop membership vectors.
     for (LoopInfo& loop : loops_) {
-      BitVector* new_members = new (zone_)
-          BitVector(static_cast<int>(schedule_->BasicBlockCount()), zone_);
-      new_members->CopyFrom(*loop.members);
-      loop.members = new_members;
+      loop.members->Resize(static_cast<int>(schedule_->BasicBlockCount()),
+                           zone_);
     }
 
     // Extend loop information vector.

test/cctest/test-bit-vector.cc

@@ -119,4 +119,27 @@ TEST(BitVector) {
     CHECK(!r.Contains(32));
     CHECK(r.Contains(33));
   }
+
+  {
+    BitVector v(35, &zone);
+    v.Add(32);
+    v.Add(33);
+    CHECK(v.Contains(32));
+    CHECK(v.Contains(33));
+    CHECK(!v.Contains(22));
+    CHECK(!v.Contains(34));
+    v.Resize(50, &zone);
+    CHECK(v.Contains(32));
+    CHECK(v.Contains(33));
+    CHECK(!v.Contains(22));
+    CHECK(!v.Contains(34));
+    CHECK(!v.Contains(43));
+    v.Resize(300, &zone);
+    CHECK(v.Contains(32));
+    CHECK(v.Contains(33));
+    CHECK(!v.Contains(22));
+    CHECK(!v.Contains(34));
+    CHECK(!v.Contains(43));
+    CHECK(!v.Contains(243));
+  }
 }