col: operate on Nulls value, not reference

This commit changes `col.Vec.SetNulls` to accept a `Nulls` struct by
value instead of by pointer. This lets us avoid a heap allocation on
each call to `Nulls.Or`.

pkg/col/coldata/nulls.go

@@ -340,12 +340,12 @@ func (n *Nulls) SetNullBitmap(bm []byte, size int) {
 
 // Or returns a new Nulls vector where NullAt(i) iff n1.NullAt(i) or
 // n2.NullAt(i).
-func (n *Nulls) Or(n2 *Nulls) *Nulls {
+func (n Nulls) Or(n2 Nulls) Nulls {
 	// For simplicity, enforce that len(n.nulls) <= len(n2.nulls).
 	if len(n.nulls) > len(n2.nulls) {
 		n, n2 = n2, n
 	}
-	res := &Nulls{
+	res := Nulls{
 		maybeHasNulls: n.maybeHasNulls || n2.maybeHasNulls,
 		nulls:         make([]byte, len(n2.nulls)),
 	}

pkg/col/coldata/nulls_test.go

@@ -161,18 +161,18 @@ func TestNullsSet(t *testing.T) {
 	}
 	for _, withSel := range []bool{false, true} {
 		t.Run(fmt.Sprintf("WithSel=%t", withSel), func(t *testing.T) {
-			var srcNulls *Nulls
+			var srcNulls Nulls
 			if withSel {
 				args.Sel = make([]int, BatchSize())
 				// Make a selection vector with every even index. (This turns nulls10 into
 				// nulls5.)
 				for i := range args.Sel {
 					args.Sel[i] = i * 2
 				}
-				srcNulls = &nulls10
+				srcNulls = nulls10
 			} else {
 				args.Sel = nil
-				srcNulls = &nulls5
+				srcNulls = nulls5
 			}
 			for _, destStartIdx := range pos {
 				for _, srcStartIdx := range pos {
@@ -241,7 +241,7 @@ func TestNullsOr(t *testing.T) {
 	n1Choice, n2Choice := rng.Intn(len(nullsToChooseFrom)), rng.Intn(len(nullsToChooseFrom))
 	n1 := nullsToChooseFrom[n1Choice].Slice(0, length1)
 	n2 := nullsToChooseFrom[n2Choice].Slice(0, length2)
-	or := n1.Or(&n2)
+	or := n1.Or(n2)
 	require.Equal(t, or.maybeHasNulls, n1.maybeHasNulls || n2.maybeHasNulls)
 	maxLength := length1
 	if length2 > length1 {

pkg/col/coldata/vec.go

@@ -128,7 +128,7 @@ type Vec interface {
 	Nulls() *Nulls
 
 	// SetNulls sets the nulls vector for this column.
-	SetNulls(*Nulls)
+	SetNulls(Nulls)
 
 	// Length returns the length of the slice that is underlying this Vec.
 	Length() int
@@ -294,8 +294,8 @@ func (m *memColumn) Nulls() *Nulls {
 	return &m.nulls
 }
 
-func (m *memColumn) SetNulls(n *Nulls) {
-	m.nulls = *n
+func (m *memColumn) SetNulls(n Nulls) {
+	m.nulls = n
 }
 
 func (m *memColumn) Length() int {

pkg/sql/colexec/colexecproj/proj_const_ops_tmpl.go

@@ -166,7 +166,7 @@ func _SET_PROJECTION(_HAS_NULLS bool) {
 	// If _HAS_NULLS is false, then there are no input Nulls. _outNulls is
 	// projVec.Nulls() so there is no need to call projVec.SetNulls().
 	// {{if _HAS_NULLS}}
-	projVec.SetNulls(_outNulls.Or(colNulls))
+	projVec.SetNulls(_outNulls.Or(*colNulls))
 	// {{end}}
 	// {{end}}
 	// {{end}}