add new mutable bitset and use it

Signed-off-by: Andres Taylor <[email protected]>

go/vt/vtgate/semantics/bitset/mutable.go

@@ -0,0 +1,56 @@
+/*
+Copyright 2024 The Vitess Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package bitset
+
+// Mutable is a growable, in-place version that we can OR bits into
+// and eventually turn into a stable (immutable) TableSet.
+type Mutable struct {
+	data []byte
+}
+
+// NewMutableTableSet creates an initially empty MutableTableSet.
+func NewMutableTableSet() *Mutable {
+	return &Mutable{}
+}
+
+// Or merges another TableSet into this Mutable, resizing if needed.
+func (m *Mutable) Or(ts Bitset) {
+	// If ts is longer than our current data, grow to accommodate it.
+	if len(ts) > len(m.data) {
+		oldData := m.data
+		m.data = make([]byte, len(ts))
+		copy(m.data, oldData)
+	}
+	// Merge in-place.
+	for i := 0; i < len(ts); i++ {
+		m.data[i] |= ts[i]
+	}
+}
+
+// AsImmutable finalizes the Mutable into a TableSet, trimming trailing zeros.
+func (m *Mutable) AsImmutable() Bitset {
+	trim := len(m.data)
+	for trim > 0 && m.data[trim-1] == 0 {
+		trim--
+	}
+	if trim == 0 {
+		// Means all bits are zero -> empty
+		return ""
+	}
+
+	return toBitset(m.data[:trim])
+}

go/vt/vtgate/semantics/semantic_table.go

@@ -19,6 +19,8 @@ package semantics
 import (
 	"fmt"
 
+	"vitess.io/vitess/go/vt/vtgate/semantics/bitset"
+
 	"vitess.io/vitess/go/mysql/collations"
 	"vitess.io/vitess/go/sqltypes"
 	"vitess.io/vitess/go/vt/key"
@@ -704,7 +706,7 @@ func (d ExprDependencies) dependencies(expr sqlparser.Expr) (deps TableSet) {
 		}()
 	}
 
-	var tables []TableSet
+	depsCalc := bitset.NewMutableTableSet()
 	// During the original semantic analysis, all ColNames were found and bound to the corresponding tables
 	// Here, we'll walk the expression tree and look to see if we can find any sub-expressions
 	// that have already set dependencies.
@@ -718,14 +720,14 @@ func (d ExprDependencies) dependencies(expr sqlparser.Expr) (deps TableSet) {
 
 		set, found := d[expr]
 		if found {
-			tables = append(tables, set)
+			depsCalc.Or(bitset.Bitset(set))
 		}
 
 		// if we found a cached value, there is no need to continue down to visit children
 		return !found, nil
 	}, expr)
 
-	deps = MergeTableSets(tables...)
+	deps = TableSet(depsCalc.AsImmutable())
 
 	return
 }