66 lines
1.8 KiB
Go
66 lines
1.8 KiB
Go
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// Copyright 2015 PingCAP, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package optimizer
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import (
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"github.com/pingcap/tidb/ast"
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"github.com/pingcap/tidb/context"
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"github.com/pingcap/tidb/evaluator"
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)
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// logicOptimize does logic optimization works on AST.
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func logicOptimize(ctx context.Context, node ast.Node) error {
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return preEvaluate(ctx, node)
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}
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// preEvaluate evaluates preEvaluable expression and rewrites constant expression to value expression.
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func preEvaluate(ctx context.Context, node ast.Node) error {
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pe := preEvaluator{ctx: ctx}
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node.Accept(&pe)
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return pe.err
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}
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type preEvaluator struct {
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ctx context.Context
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err error
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}
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func (r *preEvaluator) Enter(in ast.Node) (ast.Node, bool) {
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return in, false
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}
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func (r *preEvaluator) Leave(in ast.Node) (ast.Node, bool) {
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if expr, ok := in.(ast.ExprNode); ok {
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if _, ok = expr.(*ast.ValueExpr); ok {
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return in, true
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} else if ast.IsPreEvaluable(expr) {
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val, err := evaluator.Eval(r.ctx, expr)
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if err != nil {
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r.err = err
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return in, false
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}
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if ast.IsConstant(expr) {
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// The expression is constant, rewrite the expression to value expression.
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valExpr := &ast.ValueExpr{}
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valExpr.SetText(expr.Text())
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valExpr.SetType(expr.GetType())
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valExpr.SetValue(val)
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return valExpr, true
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}
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expr.SetValue(val)
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}
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}
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return in, true
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}
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