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constant_fold.go
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/
constant_fold.go
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// Copyright 2016 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 expression
import (
log "github.com/Sirupsen/logrus"
)
// FoldConstant does constant folding optimization on an expression.
func FoldConstant(expr Expression) Expression {
scalarFunc, ok := expr.(*ScalarFunction)
if !ok {
return expr
}
if _, ok := unFoldableFunctions[scalarFunc.FuncName.L]; ok {
return expr
}
args := scalarFunc.GetArgs()
for i := 0; i < len(args); i++ {
if _, ok := args[i].(*Constant); !ok {
return expr
}
}
value, err := scalarFunc.Eval(nil)
if err != nil {
log.Warnf("fold constant %s: %s", scalarFunc.ExplainInfo(), err.Error())
return expr
}
return &Constant{
Value: value,
RetType: scalarFunc.RetType,
}
}