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package inspector
// This file defines func typeOf(ast.Node) uint64.
//
// The initial map-based implementation was too slow;
// see https://go-review.googlesource.com/c/tools/+/135655/1/go/ast/inspector/inspector.go#196
import "go/ast"
const (
nArrayType = iota
nAssignStmt
nBadDecl
nBadExpr
nBadStmt
nBasicLit
nBinaryExpr
nBlockStmt
nBranchStmt
nCallExpr
nCaseClause
nChanType
nCommClause
nComment
nCommentGroup
nCompositeLit
nDeclStmt
nDeferStmt
nEllipsis
nEmptyStmt
nExprStmt
nField
nFieldList
nFile
nForStmt
nFuncDecl
nFuncLit
nFuncType
nGenDecl
nGoStmt
nIdent
nIfStmt
nImportSpec
nIncDecStmt
nIndexExpr
nInterfaceType
nKeyValueExpr
nLabeledStmt
nMapType
nPackage
nParenExpr
nRangeStmt
nReturnStmt
nSelectStmt
nSelectorExpr
nSendStmt
nSliceExpr
nStarExpr
nStructType
nSwitchStmt
nTypeAssertExpr
nTypeSpec
nTypeSwitchStmt
nUnaryExpr
nValueSpec
)
// typeOf returns a distinct single-bit value that represents the type of n.
//
// Various implementations were benchmarked with BenchmarkNewInspector:
// GOGC=off
// - type switch 4.9-5.5ms 2.1ms
// - binary search over a sorted list of types 5.5-5.9ms 2.5ms
// - linear scan, frequency-ordered list 5.9-6.1ms 2.7ms
// - linear scan, unordered list 6.4ms 2.7ms
// - hash table 6.5ms 3.1ms
// A perfect hash seemed like overkill.
//
// The compiler's switch statement is the clear winner
// as it produces a binary tree in code,
// with constant conditions and good branch prediction.
// (Sadly it is the most verbose in source code.)
// Binary search suffered from poor branch prediction.
//
func typeOf(n ast.Node) uint64 {
// Fast path: nearly half of all nodes are identifiers.
if _, ok := n.(*ast.Ident); ok {
return 1 << nIdent
}
// These cases include all nodes encountered by ast.Inspect.
switch n.(type) {
case *ast.ArrayType:
return 1 << nArrayType
case *ast.AssignStmt:
return 1 << nAssignStmt
case *ast.BadDecl:
return 1 << nBadDecl
case *ast.BadExpr:
return 1 << nBadExpr
case *ast.BadStmt:
return 1 << nBadStmt
case *ast.BasicLit:
return 1 << nBasicLit
case *ast.BinaryExpr:
return 1 << nBinaryExpr
case *ast.BlockStmt:
return 1 << nBlockStmt
case *ast.BranchStmt:
return 1 << nBranchStmt
case *ast.CallExpr:
return 1 << nCallExpr
case *ast.CaseClause:
return 1 << nCaseClause
case *ast.ChanType:
return 1 << nChanType
case *ast.CommClause:
return 1 << nCommClause
case *ast.Comment:
return 1 << nComment
case *ast.CommentGroup:
return 1 << nCommentGroup
case *ast.CompositeLit:
return 1 << nCompositeLit
case *ast.DeclStmt:
return 1 << nDeclStmt
case *ast.DeferStmt:
return 1 << nDeferStmt
case *ast.Ellipsis:
return 1 << nEllipsis
case *ast.EmptyStmt:
return 1 << nEmptyStmt
case *ast.ExprStmt:
return 1 << nExprStmt
case *ast.Field:
return 1 << nField
case *ast.FieldList:
return 1 << nFieldList
case *ast.File:
return 1 << nFile
case *ast.ForStmt:
return 1 << nForStmt
case *ast.FuncDecl:
return 1 << nFuncDecl
case *ast.FuncLit:
return 1 << nFuncLit
case *ast.FuncType:
return 1 << nFuncType
case *ast.GenDecl:
return 1 << nGenDecl
case *ast.GoStmt:
return 1 << nGoStmt
case *ast.Ident:
return 1 << nIdent
case *ast.IfStmt:
return 1 << nIfStmt
case *ast.ImportSpec:
return 1 << nImportSpec
case *ast.IncDecStmt:
return 1 << nIncDecStmt
case *ast.IndexExpr:
return 1 << nIndexExpr
case *ast.InterfaceType:
return 1 << nInterfaceType
case *ast.KeyValueExpr:
return 1 << nKeyValueExpr
case *ast.LabeledStmt:
return 1 << nLabeledStmt
case *ast.MapType:
return 1 << nMapType
case *ast.Package:
return 1 << nPackage
case *ast.ParenExpr:
return 1 << nParenExpr
case *ast.RangeStmt:
return 1 << nRangeStmt
case *ast.ReturnStmt:
return 1 << nReturnStmt
case *ast.SelectStmt:
return 1 << nSelectStmt
case *ast.SelectorExpr:
return 1 << nSelectorExpr
case *ast.SendStmt:
return 1 << nSendStmt
case *ast.SliceExpr:
return 1 << nSliceExpr
case *ast.StarExpr:
return 1 << nStarExpr
case *ast.StructType:
return 1 << nStructType
case *ast.SwitchStmt:
return 1 << nSwitchStmt
case *ast.TypeAssertExpr:
return 1 << nTypeAssertExpr
case *ast.TypeSpec:
return 1 << nTypeSpec
case *ast.TypeSwitchStmt:
return 1 << nTypeSwitchStmt
case *ast.UnaryExpr:
return 1 << nUnaryExpr
case *ast.ValueSpec:
return 1 << nValueSpec
}
return 0
}
func maskOf(nodes []ast.Node) uint64 {
if nodes == nil {
return 1<<64 - 1 // match all node types
}
var mask uint64
for _, n := range nodes {
mask |= typeOf(n)
}
return mask
}
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