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// 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
}
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