# 7.3 Unit Test

初始化的 UT 可以参考 IR Tree, 因为初始化工作本身就需要基于 IR Tree. 我们查看一下如下代码的处理结果：

```go
package p

const version = 1.16

func main() {
    if version <= 1.15 {
        println("Inside Body")
    } else {
        println("Inside Else")
    }
}
```

此处的 `if body` 应该从 IR Tree 中清除掉。为了方便，这里我们将所有的测试代码拷贝到测试文件 `cmd/compile/internal/noder/deadcode_test.go`, 完整内容如下：

```go
package noder

import (
    "bufio"
    "cmd/compile/internal/amd64"
    "cmd/compile/internal/base"
    "cmd/compile/internal/deadcode"
    "cmd/compile/internal/escape"
    "cmd/compile/internal/inline"
    "cmd/compile/internal/ir"
    "cmd/compile/internal/reflectdata"
    "cmd/compile/internal/ssa"
    "cmd/compile/internal/ssagen"
    "cmd/compile/internal/syntax"
    "cmd/compile/internal/typecheck"
    "cmd/compile/internal/types"
    "cmd/compile/internal/types2"
    "cmd/internal/obj"
    "cmd/internal/objabi"
    "cmd/internal/src"
    "fmt"
    "os"
    "strings"
    "testing"
)

func parseSrc(path, src string) (*syntax.File, error) {
    var mode syntax.Mode
    mode = syntax.AllowGenerics | syntax.CheckBranches
    errh := func(error) {} // dummy error handler so that parsing continues in presence of errors
    return syntax.Parse(syntax.NewFileBase(path), strings.NewReader(src), errh, nil, mode)
}

func defaultImporter() *gcimports {
    return &gcimports{
        packages: map[string]*types2.Package{},
    }
}

func init() {
    amd64.Init(&ssagen.Arch)

    base.Ctxt = obj.Linknew(ssagen.Arch.LinkArch)
    base.Ctxt.DiagFunc = base.Errorf
    base.Ctxt.DiagFlush = base.FlushErrors
    base.Ctxt.Bso = bufio.NewWriter(os.Stdout)

    base.Ctxt.UseBASEntries = base.Ctxt.Headtype != objabi.Hdarwin

    types.LocalPkg = types.NewPkg("", "")
    types.LocalPkg.Prefix = "\"\""

    types.LocalPkg.Height = types.MaxPkgHeight

    types.BuiltinPkg = types.NewPkg("go.builtin", "") // TODO(gri) name this package go.builtin?
    types.BuiltinPkg.Prefix = "go.builtin"            // not go%2ebuiltin

    // pseudo-package, accessed by import "unsafe"
    ir.Pkgs.Unsafe = types.NewPkg("unsafe", "unsafe")

    ir.Pkgs.Runtime = types.NewPkg("go.runtime", "runtime")
    ir.Pkgs.Runtime.Prefix = "runtime"

    // pseudo-packages used in symbol tables
    ir.Pkgs.Itab = types.NewPkg("go.itab", "go.itab")
    ir.Pkgs.Itab.Prefix = "go.itab" // not go%2eitab

    // pseudo-package used for methods with anonymous receivers
    ir.Pkgs.Go = types.NewPkg("go", "")

    base.DebugSSA = ssa.PhaseOption

    ssagen.Arch.LinkArch.Init(base.Ctxt)
    ir.EscFmt = escape.Fmt
    ir.IsIntrinsicCall = ssagen.IsIntrinsicCall
    inline.SSADumpInline = ssagen.DumpInline
    ssagen.InitEnv()
    ssagen.InitTables()

    types.PtrSize = ssagen.Arch.LinkArch.PtrSize
    types.RegSize = ssagen.Arch.LinkArch.RegSize
    types.MaxWidth = ssagen.Arch.MAXWIDTH

    typecheck.Target = new(ir.Package)

    typecheck.NeedITab = func(t, iface *types.Type) { reflectdata.ITabAddr(t, iface) }
    typecheck.NeedRuntimeType = reflectdata.NeedRuntimeType // TODO(rsc): TypeSym for lock?

    base.AutogeneratedPos = base.Ctxt.PosTable.XPos(src.MakePos(src.NewFileBase("<autogenerated>", "<autogenerated>"), 1, 0))

    typecheck.InitUniverse()
}

func dumpIrTree(nodes []ir.Node) {
    for _, n := range nodes {
        s := fmt.Sprintf("\nafter noder2 %v", n)
        ir.Dump(s, n)
    }
}

func TestIrTree(t *testing.T) {
    code := `
package p

const version = 1.16

func main() {
if version <= 1.15 {
println("Inside Body")
} else {
println("Inside Else")
}
}
`
    f, err := parseSrc("generic_testTypecheckConst", code)

    if err != nil {
        panic(err)
    }

    var conf types2.Config
    conf.Trace = false
    conf.Importer = defaultImporter()
    conf.Error = func(err error) {
        fmt.Printf("Typecheck Error: %v\n", err)
    }

    info := types2.Info{
        Types:      make(map[syntax.Expr]types2.TypeAndValue),
        Defs:       make(map[*syntax.Name]types2.Object),
        Uses:       make(map[*syntax.Name]types2.Object),
        Selections: make(map[*syntax.SelectorExpr]*types2.Selection),
        Implicits:  make(map[syntax.Node]types2.Object),
        Scopes:     make(map[syntax.Node]*types2.Scope),
        Inferred:   make(map[syntax.Expr]types2.Inferred),
    }

    pkg, err := conf.Check("<no package>", []*syntax.File{f}, &info)
    if err != nil {
        panic(err)
    }

    var m posMap
    g := irgen{
        target: typecheck.Target,
        self:   pkg,
        info:   &info,
        posMap: m,
        objs:   make(map[types2.Object]*ir.Name),
        typs:   make(map[types2.Type]*types.Type),
    }

    p := &noder{
        err:         make(chan syntax.Error),
        trackScopes: base.Flag.Dwarf,
        file:        f,
    }
    g.generate([]*noder{p})

    println("Before Deadcode:")
    dumpIrTree(typecheck.Target.Decls)

    for _, n := range typecheck.Target.Decls {
        if n.Op() == ir.ODCLFUNC {
            deadcode.Func(n.(*ir.Func))
        }
    }

    println("After Deadcode:")
    dumpIrTree(typecheck.Target.Decls)
}
```

如果只看 `main` 函数的 `body` 的话，前后的 IR Tree 对比如下：

&#x20;清理无效代码前：

> ```
> .   DCLFUNC-body
> .   .   IF # deadcode:27
> .   .   IF-Cond
> .   .   .   LITERAL-false tc(1) bool # deadcode:27
> .   .   IF-Body
> .   .   .   PRINTN tc(1) Use:3 # deadcode:28
> .   .   .   PRINTN-Args
> .   .   .   .   LITERAL-“Inside Body” tc(1) string # deadcode:28
> .   .   IF-Else
> .   .   .   PRINTN tc(1) Use:3 # deadcode:30
> .   .   .   PRINTN-Args
> .   .   .   .   LITERAL-“Inside Else” tc(1) string # deadcode:30
> ```

清理无效代码后：

> ```
> .   DCLFUNC-body
> .   .   IF # deadcode:27
> .   .   IF-Cond
> .   .   .   LITERAL-false tc(1) bool # deadcode:27
> .   .   IF-Else
> .   .   .   PRINTN tc(1) Use:3 # deadcode:30
> .   .   .   PRINTN-Args
> .   .   .   .   LITERAL-“Inside Else” tc(1) string # deadcode:30
> ```

后者已经没有了 `IF-Body` 这个节点。


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