66 lines
1.8 KiB
Go
66 lines
1.8 KiB
Go
// Copyright 2015 PingCAP, Inc.
|
|
//
|
|
// 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,
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
package optimizer
|
|
|
|
import (
|
|
"github.com/pingcap/tidb/ast"
|
|
"github.com/pingcap/tidb/context"
|
|
"github.com/pingcap/tidb/evaluator"
|
|
)
|
|
|
|
// logicOptimize does logic optimization works on AST.
|
|
func logicOptimize(ctx context.Context, node ast.Node) error {
|
|
return preEvaluate(ctx, node)
|
|
}
|
|
|
|
// preEvaluate evaluates preEvaluable expression and rewrites constant expression to value expression.
|
|
func preEvaluate(ctx context.Context, node ast.Node) error {
|
|
pe := preEvaluator{ctx: ctx}
|
|
node.Accept(&pe)
|
|
return pe.err
|
|
}
|
|
|
|
type preEvaluator struct {
|
|
ctx context.Context
|
|
err error
|
|
}
|
|
|
|
func (r *preEvaluator) Enter(in ast.Node) (ast.Node, bool) {
|
|
return in, false
|
|
}
|
|
|
|
func (r *preEvaluator) Leave(in ast.Node) (ast.Node, bool) {
|
|
if expr, ok := in.(ast.ExprNode); ok {
|
|
if _, ok = expr.(*ast.ValueExpr); ok {
|
|
return in, true
|
|
} else if ast.IsPreEvaluable(expr) {
|
|
val, err := evaluator.Eval(r.ctx, expr)
|
|
if err != nil {
|
|
r.err = err
|
|
return in, false
|
|
}
|
|
if ast.IsConstant(expr) {
|
|
// The expression is constant, rewrite the expression to value expression.
|
|
valExpr := &ast.ValueExpr{}
|
|
valExpr.SetText(expr.Text())
|
|
valExpr.SetType(expr.GetType())
|
|
valExpr.SetValue(val)
|
|
return valExpr, true
|
|
}
|
|
expr.SetValue(val)
|
|
}
|
|
}
|
|
return in, true
|
|
}
|