# 5.6 Unit Test

IR Tree 构建逻辑的 UT 比前面章节的要麻烦一些，因为其不仅依赖前面的词法分析、语法分析、类型检查等所有步骤，还要依赖整个编译器的全局环境初始化。

编译器的初始化工作在文件 `cmd/compile/internal/gc/main.go` 中的 `Main` 函数中完成，词法分析之前的所有逻辑都是在做初始化的工作，分割点如下所示：

```go
func Main(archInit func(*ssagen.ArchInfo)) {
    // 初始化代码，此处省略

    // 词法分析、语法分析、类型检查
    noder.LoadPackage(flag.Args())

    // 编译阶段后续步骤，此处省略
}
```

编译器的初始化工作涉及很多方面，例如与架构体系相关的初始化（例如 amd64, x86 等）、内置函数及类型、默认配置等，但也有很多代码是搭建 UT 环境不需要的，例如解析编译参数、对编译过程进行 profile 等。为了搭建 IR Tree 的 UT 环境，我们需要做如下工作：

* 精简后的初始化代码
* 语法解析、类型检查等步骤
* Dump IR Tree 的逻辑

我们创建 UT 文件 `cmd/compile/internal/noder/irgen_test.go`, 其内容如下：

```go
// file: cmd/compile/internal/noder/irgen_test.go

package noder

import (
    "bufio"
    "cmd/compile/internal/amd64"
    "cmd/compile/internal/base"
    "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

    ir.Pkgs.Unsafe = types.NewPkg("unsafe", "unsafe")

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

    ir.Pkgs.Itab = types.NewPkg("go.itab", "go.itab")
    ir.Pkgs.Itab.Prefix = "go.itab" // not go%2eitab

    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

import "fmt"

func genericFun[T any](i, j T)  {
    fmt.Printf("i: %v, j: %v\n",i, j)
}

func main() {
   genericFun(5,6)
   genericFun[float32](10.5, 11.8)
}
`
    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})

    dumpIrTree(typecheck.Target.Decls)
}
```

其中 `init` 为精简之后的编译器初始化逻辑， `parseSrc` 用来完成语法分析， `defaultImporter` 用来在类型检查时加载包。运行 `TestIrTree` 将会得到最终的 IR Tree 结构信息。


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