expression: support vectorized bitmap operations for nulls in Column

util/chunk/column.go

@@ -628,3 +628,17 @@ func (c *Column) CopyReconstruct(sel []int, dst *Column) *Column {
 	}
 	return dst
 }
+
+// MergeNulls merges these columns' null bitmaps.
+// For a row, if any column of it is null, the result is null.
+// It works like: if col1.IsNull || col2.IsNull || col3.IsNull.
+// The user should ensure that all these columns have the same length, and
+// data stored in these columns are fixed-length type.
+func (c *Column) MergeNulls(cols ...*Column) {
+	for _, col := range cols {
+		for i := range c.nullBitmap {
+			// bit 0 is null, 1 is not null, so do AND operations here.
+			c.nullBitmap[i] &= col.nullBitmap[i]
+		}
+	}
+}

util/chunk/column_test.go

@@ -885,3 +885,53 @@ func BenchmarkTimeVec(b *testing.B) {
 		}
 	}
 }
+
+func genNullCols(n int) []*Column {
+	cols := make([]*Column, n)
+	for i := range cols {
+		cols[i] = NewColumn(types.NewFieldType(mysql.TypeLonglong), 1024)
+		cols[i].ResizeInt64(1024, false)
+		for j := 0; j < 1024; j++ {
+			if rand.Intn(10) < 5 {
+				cols[i].SetNull(j, true)
+			}
+		}
+	}
+	return cols
+}
+
+func (s *testChunkSuite) TestVectorizedNulls(c *check.C) {
+	for i := 0; i < 256; i++ {
+		cols := genNullCols(4)
+		lCol, rCol := cols[0], cols[1]
+		vecResult, rowResult := cols[2], cols[3]
+		vecResult.SetNulls(0, 1024, false)
+		rowResult.SetNulls(0, 1024, false)
+		vecResult.MergeNulls(lCol, rCol)
+		for i := 0; i < 1024; i++ {
+			rowResult.SetNull(i, lCol.IsNull(i) || rCol.IsNull(i))
+		}
+
+		for i := 0; i < 1024; i++ {
+			c.Assert(rowResult.IsNull(i), check.Equals, vecResult.IsNull(i))
+		}
+	}
+}
+
+func BenchmarkMergeNullsVectorized(b *testing.B) {
+	cols := genNullCols(3)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		cols[0].MergeNulls(cols[1:]...)
+	}
+}
+
+func BenchmarkMergeNullsNonVectorized(b *testing.B) {
+	cols := genNullCols(3)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		for i := 0; i < 1024; i++ {
+			cols[0].SetNull(i, cols[1].IsNull(i) || cols[2].IsNull(i))
+		}
+	}
+}