go closure 源码

  • 2022-07-15
  • 浏览 (512)

golang closure 代码

文件路径:/src/cmd/compile/internal/walk/closure.go

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package walk

import (
	"cmd/compile/internal/base"
	"cmd/compile/internal/ir"
	"cmd/compile/internal/typecheck"
	"cmd/compile/internal/types"
	"cmd/internal/src"
)

// directClosureCall rewrites a direct call of a function literal into
// a normal function call with closure variables passed as arguments.
// This avoids allocation of a closure object.
//
// For illustration, the following call:
//
//	func(a int) {
//		println(byval)
//		byref++
//	}(42)
//
// becomes:
//
//	func(byval int, &byref *int, a int) {
//		println(byval)
//		(*&byref)++
//	}(byval, &byref, 42)
func directClosureCall(n *ir.CallExpr) {
	clo := n.X.(*ir.ClosureExpr)
	clofn := clo.Func

	if ir.IsTrivialClosure(clo) {
		return // leave for walkClosure to handle
	}

	// We are going to insert captured variables before input args.
	var params []*types.Field
	var decls []*ir.Name
	for _, v := range clofn.ClosureVars {
		if !v.Byval() {
			// If v of type T is captured by reference,
			// we introduce function param &v *T
			// and v remains PAUTOHEAP with &v heapaddr
			// (accesses will implicitly deref &v).

			addr := ir.NewNameAt(clofn.Pos(), typecheck.Lookup("&"+v.Sym().Name))
			addr.Curfn = clofn
			addr.SetType(types.NewPtr(v.Type()))
			v.Heapaddr = addr
			v = addr
		}

		v.Class = ir.PPARAM
		decls = append(decls, v)

		fld := types.NewField(src.NoXPos, v.Sym(), v.Type())
		fld.Nname = v
		params = append(params, fld)
	}

	// f is ONAME of the actual function.
	f := clofn.Nname
	typ := f.Type()

	// Create new function type with parameters prepended, and
	// then update type and declarations.
	typ = types.NewSignature(typ.Pkg(), nil, nil, append(params, typ.Params().FieldSlice()...), typ.Results().FieldSlice())
	f.SetType(typ)
	clofn.Dcl = append(decls, clofn.Dcl...)

	// Rewrite call.
	n.X = f
	n.Args.Prepend(closureArgs(clo)...)

	// Update the call expression's type. We need to do this
	// because typecheck gave it the result type of the OCLOSURE
	// node, but we only rewrote the ONAME node's type. Logically,
	// they're the same, but the stack offsets probably changed.
	if typ.NumResults() == 1 {
		n.SetType(typ.Results().Field(0).Type)
	} else {
		n.SetType(typ.Results())
	}

	// Add to Closures for enqueueFunc. It's no longer a proper
	// closure, but we may have already skipped over it in the
	// functions list as a non-trivial closure, so this just
	// ensures it's compiled.
	ir.CurFunc.Closures = append(ir.CurFunc.Closures, clofn)
}

func walkClosure(clo *ir.ClosureExpr, init *ir.Nodes) ir.Node {
	clofn := clo.Func

	// If no closure vars, don't bother wrapping.
	if ir.IsTrivialClosure(clo) {
		if base.Debug.Closure > 0 {
			base.WarnfAt(clo.Pos(), "closure converted to global")
		}
		return clofn.Nname
	}

	// The closure is not trivial or directly called, so it's going to stay a closure.
	ir.ClosureDebugRuntimeCheck(clo)
	clofn.SetNeedctxt(true)

	// The closure expression may be walked more than once if it appeared in composite
	// literal initialization (e.g, see issue #49029).
	//
	// Don't add the closure function to compilation queue more than once, since when
	// compiling a function twice would lead to an ICE.
	if !clofn.Walked() {
		clofn.SetWalked(true)
		ir.CurFunc.Closures = append(ir.CurFunc.Closures, clofn)
	}

	typ := typecheck.ClosureType(clo)

	clos := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, typ, nil)
	clos.SetEsc(clo.Esc())
	clos.List = append([]ir.Node{ir.NewUnaryExpr(base.Pos, ir.OCFUNC, clofn.Nname)}, closureArgs(clo)...)
	for i, value := range clos.List {
		clos.List[i] = ir.NewStructKeyExpr(base.Pos, typ.Field(i), value)
	}

	addr := typecheck.NodAddr(clos)
	addr.SetEsc(clo.Esc())

	// Force type conversion from *struct to the func type.
	cfn := typecheck.ConvNop(addr, clo.Type())

	// non-escaping temp to use, if any.
	if x := clo.Prealloc; x != nil {
		if !types.Identical(typ, x.Type()) {
			panic("closure type does not match order's assigned type")
		}
		addr.Prealloc = x
		clo.Prealloc = nil
	}

	return walkExpr(cfn, init)
}

// closureArgs returns a slice of expressions that an be used to
// initialize the given closure's free variables. These correspond
// one-to-one with the variables in clo.Func.ClosureVars, and will be
// either an ONAME node (if the variable is captured by value) or an
// OADDR-of-ONAME node (if not).
func closureArgs(clo *ir.ClosureExpr) []ir.Node {
	fn := clo.Func

	args := make([]ir.Node, len(fn.ClosureVars))
	for i, v := range fn.ClosureVars {
		var outer ir.Node
		outer = v.Outer
		if !v.Byval() {
			outer = typecheck.NodAddrAt(fn.Pos(), outer)
		}
		args[i] = typecheck.Expr(outer)
	}
	return args
}

func walkMethodValue(n *ir.SelectorExpr, init *ir.Nodes) ir.Node {
	// Create closure in the form of a composite literal.
	// For x.M with receiver (x) type T, the generated code looks like:
	//
	//	clos = &struct{F uintptr; R T}{T.M·f, x}
	//
	// Like walkClosure above.

	if n.X.Type().IsInterface() {
		// Trigger panic for method on nil interface now.
		// Otherwise it happens in the wrapper and is confusing.
		n.X = cheapExpr(n.X, init)
		n.X = walkExpr(n.X, nil)

		tab := ir.NewUnaryExpr(base.Pos, ir.OITAB, n.X)
		check := ir.NewUnaryExpr(base.Pos, ir.OCHECKNIL, tab)
		init.Append(typecheck.Stmt(check))
	}

	typ := typecheck.MethodValueType(n)

	clos := ir.NewCompLitExpr(base.Pos, ir.OCOMPLIT, typ, nil)
	clos.SetEsc(n.Esc())
	clos.List = []ir.Node{ir.NewUnaryExpr(base.Pos, ir.OCFUNC, methodValueWrapper(n)), n.X}

	addr := typecheck.NodAddr(clos)
	addr.SetEsc(n.Esc())

	// Force type conversion from *struct to the func type.
	cfn := typecheck.ConvNop(addr, n.Type())

	// non-escaping temp to use, if any.
	if x := n.Prealloc; x != nil {
		if !types.Identical(typ, x.Type()) {
			panic("partial call type does not match order's assigned type")
		}
		addr.Prealloc = x
		n.Prealloc = nil
	}

	return walkExpr(cfn, init)
}

// methodValueWrapper returns the ONAME node representing the
// wrapper function (*-fm) needed for the given method value. If the
// wrapper function hasn't already been created yet, it's created and
// added to typecheck.Target.Decls.
func methodValueWrapper(dot *ir.SelectorExpr) *ir.Name {
	if dot.Op() != ir.OMETHVALUE {
		base.Fatalf("methodValueWrapper: unexpected %v (%v)", dot, dot.Op())
	}

	t0 := dot.Type()
	meth := dot.Sel
	rcvrtype := dot.X.Type()
	sym := ir.MethodSymSuffix(rcvrtype, meth, "-fm")

	if sym.Uniq() {
		return sym.Def.(*ir.Name)
	}
	sym.SetUniq(true)

	if base.Debug.Unified != 0 {
		base.FatalfAt(dot.Pos(), "missing wrapper for %v", meth)
	}

	savecurfn := ir.CurFunc
	saveLineNo := base.Pos
	ir.CurFunc = nil

	base.Pos = base.AutogeneratedPos

	fn := typecheck.DeclFunc(sym, nil,
		typecheck.NewFuncParams(t0.Params(), true),
		typecheck.NewFuncParams(t0.Results(), false))
	fn.SetDupok(true)
	fn.SetWrapper(true)

	// Declare and initialize variable holding receiver.
	ptr := ir.NewHiddenParam(base.Pos, fn, typecheck.Lookup(".this"), rcvrtype)

	call := ir.NewCallExpr(base.Pos, ir.OCALL, ir.NewSelectorExpr(base.Pos, ir.OXDOT, ptr, meth), nil)
	call.Args = ir.ParamNames(fn.Type())
	call.IsDDD = fn.Type().IsVariadic()

	var body ir.Node = call
	if t0.NumResults() != 0 {
		ret := ir.NewReturnStmt(base.Pos, nil)
		ret.Results = []ir.Node{call}
		body = ret
	}

	fn.Body = []ir.Node{body}
	typecheck.FinishFuncBody()

	typecheck.Func(fn)
	// Need to typecheck the body of the just-generated wrapper.
	// typecheckslice() requires that Curfn is set when processing an ORETURN.
	ir.CurFunc = fn
	typecheck.Stmts(fn.Body)
	sym.Def = fn.Nname
	typecheck.Target.Decls = append(typecheck.Target.Decls, fn)
	ir.CurFunc = savecurfn
	base.Pos = saveLineNo

	return fn.Nname
}

相关信息

go 源码目录

相关文章

go assign 源码

go builtin 源码

go compare 源码

go complit 源码

go convert 源码

go expr 源码

go order 源码

go race 源码

go range 源码

go select 源码