Fix SelectivityVector::resize (facebookincubator#1303)

Summary:
I noticed that sometimes the number of output rows for streaming aggregation is
greater than number of input rows. This should never be the case as aggregation
must not increase cardinality. Turns out there was a bug in
SelectivityVector::resize() which is used in GroupingSet::addRemainingInput().

SelectivityVector::resize() when called on a vector whose size is a
multiple of 64 incorrectly marked last 64 bits as "selected" before resizing.

This commit fixes SelectivityVector::resize() and updates
GroupingSet::addRemainingInput() to call resize() before cleanAll() "just in case".

Pull Request resolved: facebookincubator#1303

Reviewed By: kgpai

Differential Revision: D35205252

Pulled By: mbasmanova

fbshipit-source-id: a74226813039c3aa28b430a060fdb4101226754f

velox/exec/GroupingSet.cpp

@@ -213,8 +213,8 @@ void GroupingSet::addInputForActiveRows(
 }
 
 void GroupingSet::addRemainingInput() {
-  activeRows_.clearAll();
   activeRows_.resize(remainingInput_->size());
+  activeRows_.clearAll();
   activeRows_.setValidRange(firstRemainingRow_, remainingInput_->size(), true);
   activeRows_.updateBounds();
 

velox/vector/SelectivityVector.h

@@ -65,7 +65,10 @@ class SelectivityVector {
     auto numWords = bits::nwords(size);
     // Set bits from size_ to end of the word.
     if (size > size_ && !bits_.empty()) {
-      bits::fillBits(&bits_.back(), size_ % 64, 64, value);
+      const auto start = size_ % 64;
+      if (start) {
+        bits::fillBits(&bits_.back(), start, 64, value);
+      }
     }
 
     bits_.resize(numWords, value ? -1 : 0);

velox/vector/tests/SelectivityVectorTest.cpp

@@ -65,8 +65,11 @@ void assertIsValid(
     int to,
     const SelectivityVector& vector,
     bool value) {
+  for (int i = 0; i < from; i++) {
+    EXPECT_EQ(!value, vector.isValid(i)) << "at " << i;
+  }
   for (int i = from; i < to; i++) {
-    ASSERT_EQ(value, vector.isValid(i));
+    EXPECT_EQ(value, vector.isValid(i)) << "at " << i;
   }
 }
 
@@ -398,8 +401,7 @@ TEST(SelectivityVectorTest, resize) {
   SelectivityVector larger(53, true);
   assertIsValid(0, 53, larger, true);
   larger.resize(656, true);
-  assertIsValid(53, 64, larger, true);
-  assertIsValid(640, 656, larger, true);
+  assertIsValid(0, 656, larger, true);
 
   // Check for word length reduction
   larger.resize(53);
@@ -420,7 +422,7 @@ TEST(SelectivityVectorTest, select) {
   a.resize(33, true);
   SelectivityVector b(32, false);
   b.select(a);
-  assertIsValid(17, 32, b, true);
+  assertIsValid(16, 32, b, true);
 
   SelectivityVector empty(0);
   empty.select(first);