Golang Expr.List方法代码示例

func tryPrintf(curfn *cc.Decl, x *cc.Expr, name string, fmtpos int, newName string) bool {
	if (x.Left.Text == name || (strings.Contains(name, ".") || strings.Contains(name, "->")) && x.Left.String() == name) && len(x.List) >= fmtpos+1 && x.List[fmtpos].Op == cc.String {
		x.List = append(x.List[:fmtpos+1], fixPrintFormat(curfn, x.List[fmtpos], x.List[fmtpos+1:])...)
		if newName != "" {
			x.Left.Text = newName
			x.Left.XDecl = nil
		}
		return true
	}
	return false
}

func fixSpecialCall(fn *cc.Decl, x *cc.Expr, targ *cc.Type) bool {
	if x.Left.Op != cc.Name {
		return false
	}
	switch x.Left.Text {
	case "memmove":
		if len(x.List) != 3 {
			// fprintf(x.Span, "unsupported %v", x)
			return false
		}
		siz := x.List[2]
		if siz.Op == cc.Number && siz.Text == "4" {
			obj1, obj1Type := objIndir(fn, x.List[0])
			obj2, obj2Type := objIndir(fn, x.List[1])
			if obj1Type == nil || obj2Type == nil {
				// fprintf(x.Span, "unsupported %v - missing types", x)
				return true
			}
			if (obj1Type.Kind == Uint32 || obj1Type.Kind == Int32) && obj2Type.Kind == Float32 {
				x.Op = cc.Eq
				x.Left = obj1
				x.Right = &cc.Expr{
					Op: cc.Call,
					Left: &cc.Expr{Op: cc.Name,
						Text: "math.Float32bits",
					},
					List: []*cc.Expr{obj2},
				}
				x.XType = uint32Type
				return true
			}
			// fprintf(x.Span, "unsupported %v - size 4 type %v %v", x, GoString(obj1Type), GoString(obj2Type))
		}
		if siz.Op == cc.Number && siz.Text == "8" {
			obj1, obj1Type := objIndir(fn, x.List[0])
			obj2, obj2Type := objIndir(fn, x.List[1])
			if obj1Type == nil || obj2Type == nil {
				// fprintf(x.Span, "unsupported %v - missing types", x)
				return true
			}
			if (obj1Type.Kind == Uint64 || obj1Type.Kind == Int64) && obj2Type.Kind == Float64 {
				x.Op = cc.Eq
				x.Left = obj1
				x.Right = &cc.Expr{
					Op: cc.Call,
					Left: &cc.Expr{Op: cc.Name,
						Text: "math.Float64bits",
					},
					List: []*cc.Expr{obj2},
				}
				x.XType = uint64Type
				return true
			}
			// fprintf(x.Span, "unsupported %v - size 8 type %v %v", x, GoString(obj1Type), GoString(obj2Type))
		}
		if siz.Op == cc.SizeofExpr {
			obj1Type := fixGoTypesExpr(fn, x.List[0], nil)
			obj2Type := fixGoTypesExpr(fn, x.List[1], nil)
			sizeType := fixGoTypesExpr(fn, siz.Left, nil)
			if obj1Type == nil || obj2Type == nil {
				// fprintf(x.Span, "unsupported %v - bad types", x)
				return true
			}
			if obj2Type.Kind == cc.Array && sameType(obj2Type, sizeType) || obj2Type.Kind == Slice && GoString(x.List[1]) == GoString(siz.Left) {
				x.Left.Text = "copy"
				x.Left.XDecl = nil
				x.List = x.List[:2]
				return true
			}
			// fprintf(x.Span, "unsupported %v - not array %v %v", x, GoString(obj2Type), GoString(sizeType))
			return true
		}
		left := fixGoTypesExpr(fn, x.List[0], nil)
		right := fixGoTypesExpr(fn, x.List[1], nil)
		fixGoTypesExpr(fn, siz, nil)
		if isSliceOrArray(left) && isSliceOrArray(right) && left.Base.Is(Uint8) && right.Base.Is(Uint8) {
			x.Left.Text = "copy"
			x.Left.XDecl = nil
			if x.List[1].Op == ExprSlice && x.List[1].List[1] == nil {
				x.List[1].List[2] = siz
			} else {
				x.List[1] = &cc.Expr{Op: ExprSlice, List: []*cc.Expr{x.List[1], nil, siz}}
			}
			x.List = x.List[:2]
			return true
		}
		// fprintf(x.Span, "unsupported %v (%v %v)", x, GoString(left), GoString(right))
		return true

	case "mal", "malloc", "emallocz", "xmalloc":
		if len(x.List) != 1 {
			fprintf(x.Span, "unsupported %v - too many args", x)
			return false
		}
		siz := x.List[0]
		var count *cc.Expr
		if siz.Op == cc.Mul {
			count = siz.Left
			siz = siz.Right
			if count.Op == cc.SizeofType || count.Op == cc.SizeofExpr {
//.........这里部分代码省略.........

func forceConvert(fn *cc.Decl, x *cc.Expr, actual, targ *cc.Type) {
	if isEmptyInterface(targ) {
		return
	}
	if isEmptyInterface(actual) {
		old := copyExpr(x)
		x.Op = TypeAssert
		x.Left = old
		x.Right = nil
		x.List = nil
		x.Type = targ
		x.XType = targ
		return
	}

	if isNumericConst(x) && targ != nil {
		switch targ.Kind {
		case cc.Ptr, Slice:
			if x.Op == cc.Number && x.Text == "0" {
				x.Op = cc.Name
				x.Text = "nil"
				x.XType = targ
			}
		case String:
			if x.Op == cc.Number && x.Text == "0" {
				x.Op = cc.Name
				x.Text = `""`
				x.XType = targ
			}
		}
		return
	}

	if x.Op == cc.Name && x.Text == "nil" && targ != nil {
		switch targ.Kind {
		case cc.Func, cc.Ptr, Slice:
			return
		case String:
			x.Text = `""`
			x.XType = targ
			x.XDecl = nil
			return
		}
	}

	if actual == nil || targ == nil {
		return
	}

	if actual.Kind == Ideal && Int8 <= targ.Kind && targ.Kind <= Float64 {
		return
	}

	if x != nil && x.Op == cc.Name && x.Text == "nil" {
		if targ.Kind == cc.Func || targ.Kind == cc.Ptr || targ.Kind == Slice {
			return
		}
	}

	// Func conversions are never useful.
	// If the func types are different, the conversion will fail;
	// if not, the conversion is unnecessary.
	// Either way the conversion is an eyesore.
	if targ.Kind == cc.Func || targ.Kind == cc.Ptr && targ.Base.Kind == cc.Func {
		return
	}

	if actual.Kind == Bool && Int8 <= targ.Kind && targ.Kind <= Float64 {
		old := copyExpr(x)
		if targ.Kind == Int {
			x.Op = cc.Call
			x.Left = &cc.Expr{Op: cc.Name, Text: "bool2int"}
			x.List = []*cc.Expr{old}
			x.Right = nil
		} else {
			x.Op = cc.Cast
			x.Left = &cc.Expr{Op: cc.Call, Left: &cc.Expr{Op: cc.Name, Text: "bool2int"}, List: []*cc.Expr{old}}
			x.Type = targ
		}
		return
	}

	if actual.Kind == cc.Array && targ.Kind == Slice && sameType(actual.Base, targ.Base) {
		old := copyExpr(x)
		x.Op = ExprSlice
		x.List = []*cc.Expr{old, nil, nil}
		x.Left = nil
		x.Right = nil
		return
	}

	if actual.Kind == Slice && targ.Kind == cc.Ptr && sameType(actual.Base, targ.Base) {
		if isCall(x, "make") {
			return
		}
		old := copyExpr(x)
		x.Op = cc.Addr
		x.Left = &cc.Expr{Op: cc.Index, Left: old, Right: &cc.Expr{Op: cc.Number, Text: "0"}}
		return
	}
//.........这里部分代码省略.........

func fixGoTypesExpr(fn *cc.Decl, x *cc.Expr, targ *cc.Type) (ret *cc.Type) {
	if x == nil {
		return nil
	}

	defer func() {
		x.XType = ret
	}()

	if x.Op == cc.Paren {
		return fixGoTypesExpr(fn, x.Left, targ)
	}

	// Make explicit C's implicit conversions from boolean to non-boolean and vice versa.
	switch x.Op {
	case cc.AndAnd, cc.OrOr, cc.Not, cc.EqEq, cc.Lt, cc.LtEq, cc.Gt, cc.GtEq, cc.NotEq:
		if targ != nil && targ.Kind != Bool {
			old := copyExpr(x)
			if targ.Kind == Int {
				x.Op = cc.Call
				x.Left = &cc.Expr{Op: cc.Name, Text: "bool2int"}
				x.List = []*cc.Expr{old}
				x.Right = nil
			} else {
				x.Op = cc.Cast
				x.Left = &cc.Expr{Op: cc.Call, Left: &cc.Expr{Op: cc.Name, Text: "bool2int"}, List: []*cc.Expr{old}}
				x.Type = targ
			}
			fixGoTypesExpr(fn, old, boolType)
			return targ
		}
	default:
		if targ != nil && targ.Kind == Bool {
			old := copyExpr(x)
			left := fixGoTypesExpr(fn, old, nil)
			if left != nil && left.Kind == Bool {
				return targ
			}
			if old.Op == cc.Number {
				switch old.Text {
				case "1":
					x.Op = cc.Name
					x.Text = "true"
					return targ
				case "0":
					x.Op = cc.Name
					x.Text = "false"
					return targ
				}
			}
			x.Op = cc.NotEq
			x.Left = old
			x.Right = zeroFor(left)
			fixSpecialCompare(fn, x)
			return targ
		}
	}

	fixArray(fn, x)

	switch x.Op {
	default:
		panic(fmt.Sprintf("unexpected construct %v in fixGoTypesExpr - %v - %v", GoString(x), x.Op, x.Span))

	case ExprType:
		// inserted by a rewrite
		return nil

	case ExprSlice:
		// inserted by rewriteLen
		left := fixGoTypesExpr(fn, x.List[0], targ)
		fixGoTypesExpr(fn, x.List[1], nil)
		fixGoTypesExpr(fn, x.List[2], nil)
		return left

	case cc.Comma:
		for i, y := range x.List {
			t := targ
			if i+1 < len(x.List) {
				t = nil
			}
			fixGoTypesExpr(fn, y, t)
		}
		return nil

	case ExprBlock:
		for _, stmt := range x.Block {
			fixGoTypesStmt(nil, fn, stmt)
		}
		return nil

	case cc.Add, cc.And, cc.Div, cc.Mod, cc.Mul, cc.Or, cc.Sub, cc.Xor:
		if x.Op == cc.Sub && isPtrSliceOrArray(x.Left.XType) && isPtrSliceOrArray(x.Right.XType) {
			left := fixGoTypesExpr(fn, x.Left, nil)
			right := fixGoTypesExpr(fn, x.Right, nil)
			if left != nil && right != nil && left.Kind != right.Kind {
				if left.Kind == Slice {
					forceConvert(fn, x.Right, right, left)
				} else {
					forceConvert(fn, x.Left, left, right)
//.........这里部分代码省略.........

func fixSpecialCompare(fn *cc.Decl, x *cc.Expr) bool {
	if (x.Right.Op != cc.Number || x.Right.Text != "0") && x.Right.String() != "nil" && x.Right.String() != `""` || x.Left.Op != cc.Call || x.Left.Left.Op != cc.Name {
		return false
	}

	call := x.Left
	switch call.Left.Text {
	case "memcmp":
		if len(call.List) != 3 {
			// fprintf(x.Span, "unsupported %v", x)
			return false
		}
		obj1, obj1Type := objIndir(fn, call.List[0])
		obj2, obj2Type := objIndir(fn, call.List[1])
		if obj1Type == nil || !sameType(obj1Type, obj2Type) {
			// fprintf(x.Span, "unsupported %v", call)
			return true
		}

		if !matchSize(fn, obj1, obj1Type, call.List[2]) && !matchSize(fn, obj2, obj2Type, call.List[2]) {
			// fprintf(x.Span, "unsupported %v - wrong size", call)
			return true
		}

		x.Left = obj1
		x.Right = obj2
		x.List = nil
		x.XType = boolType
		return true

	case "strncmp":
		if len(call.List) != 3 {
			fprintf(x.Span, "unsupported %v", x)
			return false
		}
		call.Left = &cc.Expr{Op: cc.Name, Text: "strings.HasPrefix"}
		call.List = call.List[:2]
		call.XType = boolType
		if x.Op == cc.EqEq {
			*x = *call
		} else if x.Op == cc.NotEq {
			x.Op = cc.Not
			x.Right = nil
		}
		x.XType = boolType
		return true

	case "strstr":
		if len(call.List) != 2 {
			fprintf(x.Span, "unsupported %v", x)
			return false
		}
		call.Left = &cc.Expr{Op: cc.Name, Text: "strings.Contains"}
		call.XType = boolType
		if x.Op == cc.NotEq {
			*x = *call
		} else if x.Op == cc.EqEq {
			x.Op = cc.Not
			x.Right = nil
		}
		x.XType = boolType
		return true

	case "utfrune":
		if len(call.List) != 2 {
			fprintf(x.Span, "unsupported %v", x)
			return false
		}
		call.Left = &cc.Expr{Op: cc.Name, Text: "strings.ContainsRune"}
		call.XType = boolType
		if x.Op == cc.NotEq {
			*x = *call
		} else if x.Op == cc.EqEq {
			x.Op = cc.Not
			x.Right = nil
		}
		x.XType = boolType
		return true

	case "ucistrcmp":
		if len(call.List) != 2 {
			fprintf(x.Span, "unsupported %v", x)
			return false
		}
		call.Left = &cc.Expr{Op: cc.Name, Text: "strings.EqualFold"}
		call.XType = boolType
		if x.Op == cc.EqEq {
			*x = *call
		} else if x.Op == cc.NotEq {
			x.Op = cc.Not
			x.Right = nil
		}
		x.XType = boolType
		return true

	case "strcmp":
		if len(call.List) != 2 {
			fprintf(x.Span, "unsupported %v", x)
			return false
		}
//.........这里部分代码省略.........

// fixArrays rewrites uses of the untyped "Array" container defined in cmd/gc
// to use native Go slices.
// It has nothing to do with standard C arrays.
func fixArray(fn *cc.Decl, x *cc.Expr) {
	// arraynew(n, sizeof(T)) becomes Go make([]T, 0, n).
	if isCall(x, "arraynew") {
		if len(x.List) != 2 {
			fprintf(x.Span, "wrong number of arguments to arraynew")
			return
		}
		if x.List[1].Op != cc.SizeofType {
			fprintf(x.Span, "second argument to arraynew must be sizeof(T)")
			return
		}
		x.Left.Text = "make"
		x.Left.XDecl = nil
		typ := &cc.Type{Kind: Slice, Base: x.List[1].Type}
		x.XType = typ
		x.List = append(x.List, x.List[0])
		x.List[1] = &cc.Expr{Op: cc.Number, Text: "0"}
		x.List[0] = &cc.Expr{Op: ExprType, Type: typ}
		return
	}

	// arraylength(x) becomes len(x)
	if isCall(x, "arraylength") {
		x.Left.Text = "len"
		x.Left.XDecl = nil
		return
	}

	// arrayset is unused in practice!

	// arrayadd(x, &elem) becomes x = append(x, elem).
	// Strictly speaking, this is not a complete translation,
	// because in the C code x might be a pointer taken from
	// another place, and arrayadd changes the len at that
	// other place too. In cmd/gc this does not happen.
	if isCall(x, "arrayadd") {
		if len(x.List) != 2 {
			fprintf(x.Span, "wrong number of arguments to arrayadd")
			return
		}
		if x.List[1].Op != cc.Addr {
			fprintf(x.Span, "second argument to arrayadd must be &x, have %v", x.List[1])
			return
		}
		append := copyExpr(x)
		append.Left.Text = "append"
		append.Left.XDecl = nil
		x.Op = cc.Eq
		x.Left = append.List[0]
		x.Right = append
		append.List[1] = append.List[1].Left
		return
	}

	// *(T**)(arrayget(x, i)) turns into x[i].
	// Record that x should have translated type T*.
	if x.Op == cc.Indir && x.Left.Op == cc.Cast && x.Left.Type.Kind == cc.Ptr && x.Left.Type.Base.Kind == cc.Ptr && isCall(x.Left.Left, "arrayget") {
		call := x.Left.Left
		x.Op = cc.Index
		x.XType = x.Left.Type.Base
		x.Left = call.List[0]
		x.Right = call.List[1]
		saveSliceType(x.Left, x.XType)
		return
	}

	// TODO: arraysort
}

func fixQsort(prog *cc.Prog, x *cc.Expr) {
	if len(x.List) != 4 {
		fprintf(x.Span, "unsupported %v - wrong arg count", x)
		return
	}
	if x.List[2].Op != cc.SizeofExpr || unparen(x.List[2].Left).String() != unparen(x.List[0]).String()+"[0]" {
		fprintf(x.Span, "unsupported %v - wrong elem size %v vs %v", x, unparen(x.List[2].Left).String(), unparen(x.List[0]).String()+"[0]")
		return
	}
	if x.List[3].Op != cc.Name || x.List[3].XDecl == nil {
		fprintf(x.Span, "unsupported %v - unknown comparison function", x)
		return
	}
	cmp := x.List[3].XDecl.Name
	decl := x.List[3].XDecl

	typ, newDecl := fixQsortCmp(decl)
	if typ == nil {
		return
	}

	x.Left.Text = "sort.Sort"
	x.Left.XDecl = nil
	x.List = []*cc.Expr{
		&cc.Expr{
			Op:   cc.Call,
			Left: &cc.Expr{Op: cc.Name, Text: cmp},
			List: []*cc.Expr{
				{
					Op: ExprSlice,
					List: []*cc.Expr{
						x.List[0],
						nil,
						x.List[1],
					},
				},
			},
		},
	}

	typeDecl := &cc.Decl{
		GoPackage:  decl.GoPackage,
		SyntaxInfo: cc.SyntaxInfo{Span: decl.Span},
		Name:       cmp,
		Storage:    cc.Typedef,
		Type: &cc.Type{
			Kind: Slice,
			Base: typ,
		},
	}

	lenFunc := &cc.Decl{
		GoPackage:  decl.GoPackage,
		SyntaxInfo: cc.SyntaxInfo{Span: decl.Span},
		Name:       "(x " + cmp + ") Len",
		Type: &cc.Type{
			Kind: cc.Func,
			Base: intType,
		},
		Body: &cc.Stmt{
			Op: cc.Block,
			Block: []*cc.Stmt{
				{
					Op: cc.Return,
					Expr: &cc.Expr{
						Op:   cc.Name,
						Text: "len(x)",
					},
				},
			},
		},
	}

	swapFunc := &cc.Decl{
		GoPackage:  decl.GoPackage,
		SyntaxInfo: cc.SyntaxInfo{Span: decl.Span},
		Name:       "(x " + cmp + ") Swap",
		Type: &cc.Type{
			Kind: cc.Func,
			Base: &cc.Type{Kind: cc.Void},
			Decls: []*cc.Decl{
				{Name: "i", Type: &cc.Type{Kind: cc.TypedefType}},
				{Name: "j", Type: intType},
			},
		},
		Body: &cc.Stmt{
			Op: cc.Block,
			Block: []*cc.Stmt{
				{
					Op: cc.StmtExpr,
					Expr: &cc.Expr{
						Op:   cc.Name,
						Text: "x[i], x[j] = x[j], x[i]",
					},
				},
			},
		},
	}

	for i, d := range prog.Decls {
//.........这里部分代码省略.........

func fixPrintf(curfn *cc.Decl, x *cc.Expr) bool {
	if x.Op != cc.Call {
		return false
	}
	if tryPrintf(curfn, x, "sprint", 1, "fmt.Sprintf") {
		targ := x.List[0]
		x.List = x.List[1:]
		x.Right = copyExpr(x)
		x.List = nil
		x.Left = targ
		x.Op = cc.Eq

		// sprint(strchr(s, 0), "hello") => s += "hello"
		if targ.Op == cc.Call && len(targ.List) == 2 && targ.Left.Text == "strchr" && targ.List[1].Text == "0" {
			x.Left = targ.List[0]
			x.Op = cc.AddEq
		} else if targ.Op == cc.Add && targ.Right.Op == cc.Call && targ.Right.Left.Text == "strlen" && len(targ.Right.List) == 1 && GoString(targ.Left) == GoString(targ.Right.List[0]) {
			x.Left = targ.Left
			x.Op = cc.AddEq
		}
		return true
	}
	if tryPrintf(curfn, x, "snprint", 2, "fmt.Sprintf") {
		targ := x.List[0]
		x.List = x.List[2:]
		x.Right = copyExpr(x)
		x.List = nil
		x.Left = targ
		x.Op = cc.Eq
		return true
	}
	if tryPrintf(curfn, x, "fmtprint", 1, "fmt.Sprintf") {
		targ := x.List[0]
		x.List = x.List[1:]
		x.Right = copyExpr(x)
		x.List = nil
		x.Left = targ
		x.Op = cc.AddEq
		if x.Left.Op == cc.Addr {
			x.Left = x.Left.Left
		}
		return true
	}
	if tryPrintf(curfn, x, "smprint", 0, "fmt.Sprintf") {
		x.XType = stringType
		return true
	}
	if tryPrintf(curfn, x, "print", 0, "fmt.Printf") {
		return true
	}
	if tryPrintf(curfn, x, "fprint", 1, "fmt.Fprintf") {
		if x.List[0].String() == "2" {
			x.List[0] = &cc.Expr{Op: cc.Name, Text: "os.Stderr"}
		}
		return true
	}
	if tryPrintf(curfn, x, "sysfatal", 0, "log.Fatalf") {
		return true
	}
	if tryPrintf(curfn, x, "fatal", 0, "") {
		return true
	}
	if tryPrintf(curfn, x, "ctxt->diag", 0, "") {
		return true
	}
	if tryPrintf(curfn, x, "diag", 0, "") {
		return true
	}
	if tryPrintf(curfn, x, "werrstr", 0, "") {
		return true
	}
	if tryPrintf(curfn, x, "yyerror", 0, "") {
		return true
	}
	if tryPrintf(curfn, x, "yyerrorl", 1, "") {
		forceConvert(curfn, x.List[0], x.List[0].XType, intType)
		return true
	}
	if tryPrintf(curfn, x, "onearg", 1, "") {
		return true
	}
	if tryPrintf(curfn, x, "warn", 0, "") {
		return true
	}
	if tryPrintf(curfn, x, "warnl", 1, "") {
		forceConvert(curfn, x.List[0], x.List[0].XType, intType)
		return true
	}
	if tryPrintf(curfn, x, "Bprint", 1, "fmt.Fprintf") {
		return true
	}

	if isCall(x, "exprfmt") && len(x.List) == 3 {
		// exprfmt(fp, x, y) becomes fp += exprfmt(x, y)
		x.Op = cc.AddEq
		x.Right = &cc.Expr{Op: cc.Call, Left: x.Left, List: x.List[1:]}
		x.Left = x.List[0]
		x.List = nil
		x.XType = stringType
		return true
//.........这里部分代码省略.........

func doSideEffects(x *cc.Expr, before, after *[]*cc.Stmt, mode int) {
	if x == nil {
		return
	}

	// Cannot hoist side effects from conditionally evaluated expressions
	// into unconditionally evaluated statement lists.
	// For now, detect but do not handle.
	switch x.Op {
	case cc.Cond:
		doSideEffects(x.List[0], before, after, mode&^sideStmt|sideNoAfter)
		checkNoSideEffects(x.List[1], 0)
		checkNoSideEffects(x.List[2], 0)

	case cc.AndAnd, cc.OrOr:
		doSideEffects(x.Left, before, after, mode&^sideStmt|sideNoAfter)
		checkNoSideEffects(x.Right, 0)

	case cc.Comma:
		var leftover []*cc.Expr
		for i, y := range x.List {
			m := mode | sideNoAfter
			if i+1 < len(x.List) {
				m |= sideStmt
			}
			doSideEffects(y, before, after, m)
			switch y.Op {
			case cc.PostInc, cc.PostDec, cc.Eq, cc.AddEq, cc.SubEq, cc.MulEq, cc.DivEq, cc.ModEq, cc.XorEq, cc.OrEq, cc.AndEq, cc.LshEq, cc.RshEq:
				*before = append(*before, &cc.Stmt{Op: cc.StmtExpr, Expr: y})
			default:
				leftover = append(leftover, y)
			}
		}
		x.List = leftover

	default:
		doSideEffects(x.Left, before, after, mode&^sideStmt)
		doSideEffects(x.Right, before, after, mode&^sideStmt)
		for _, y := range x.List {
			doSideEffects(y, before, after, mode&^sideStmt)
		}
	}

	if mode&sideStmt != 0 {
		// Expression as statement.
		// Can leave x++ alone, can rewrite ++x to x++, can leave x [op]= y alone.
		switch x.Op {
		case cc.PreInc:
			x.Op = cc.PostInc
			return
		case cc.PreDec:
			x.Op = cc.PostDec
			return
		case cc.PostInc, cc.PostDec:
			return
		case cc.Eq, cc.AddEq, cc.SubEq, cc.MulEq, cc.DivEq, cc.ModEq, cc.XorEq, cc.OrEq, cc.AndEq, cc.LshEq, cc.RshEq:
			return
		case cc.Call:
			return
		}
	}

	switch x.Op {
	case cc.Eq, cc.AddEq, cc.SubEq, cc.MulEq, cc.DivEq, cc.ModEq, cc.XorEq, cc.OrEq, cc.AndEq, cc.LshEq, cc.RshEq:
		x.Left = forceCheap(before, x.Left)
		old := copyExpr(x)
		*before = append(*before, &cc.Stmt{Op: cc.StmtExpr, Expr: old})
		fixMerge(x, x.Left)

	case cc.PreInc, cc.PreDec:
		x.Left = forceCheap(before, x.Left)
		old := copyExpr(x)
		old.SyntaxInfo = cc.SyntaxInfo{}
		if old.Op == cc.PreInc {
			old.Op = cc.PostInc
		} else {
			old.Op = cc.PostDec
		}
		*before = append(*before, &cc.Stmt{Op: cc.StmtExpr, Expr: old})
		fixMerge(x, x.Left)

	case cc.PostInc, cc.PostDec:
		x.Left = forceCheap(before, x.Left)
		if mode&sideNoAfter != 0 {
			// Not allowed to generate fixups afterward.
			d := &cc.Decl{
				Name: fmt.Sprintf("tmp%d", <-tmpGen),
				Type: x.Left.XType,
			}
			eq := &cc.Expr{
				Op:    ColonEq,
				Left:  &cc.Expr{Op: cc.Name, Text: d.Name, XDecl: d},
				Right: x.Left,
			}
			old := copyExpr(x.Left)
			old.SyntaxInfo = cc.SyntaxInfo{}
			*before = append(*before,
				&cc.Stmt{Op: cc.StmtExpr, Expr: eq},
				&cc.Stmt{Op: cc.StmtExpr, Expr: &cc.Expr{Op: x.Op, Left: old}},
			)
//.........这里部分代码省略.........