src/cmd/compile/internal/gc/walk.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 gc

import (
	"cmd/internal/obj"
	"cmd/internal/sys"
	"fmt"
	"strings"
)

// The constant is known to runtime.
const (
	tmpstringbufsize = 32
)

func walk(fn *Node) {
	Curfn = fn

	if Debug['W'] != 0 {
		s := fmt.Sprintf("\nbefore %v", Curfn.Func.Nname.Sym)
		dumplist(s, Curfn.Nbody)
	}

	lno := lineno

	// Final typecheck for any unused variables.
	// It's hard to be on the heap when not-used, but best to be consistent about &~PHEAP here and below.
	for i, ln := range fn.Func.Dcl {
		if ln.Op == ONAME && ln.Class&^PHEAP == PAUTO {
			ln = typecheck(ln, Erv|Easgn)
			fn.Func.Dcl[i] = ln
		}
	}

	// Propagate the used flag for typeswitch variables up to the NONAME in it's definition.
	for _, ln := range fn.Func.Dcl {
		if ln.Op == ONAME && ln.Class&^PHEAP == PAUTO && ln.Name.Defn != nil && ln.Name.Defn.Op == OTYPESW && ln.Used {
			ln.Name.Defn.Left.Used = true
		}
	}

	for _, ln := range fn.Func.Dcl {
		if ln.Op != ONAME || ln.Class&^PHEAP != PAUTO || ln.Sym.Name[0] == '&' || ln.Used {
			continue
		}
		if defn := ln.Name.Defn; defn != nil && defn.Op == OTYPESW {
			if defn.Left.Used {
				continue
			}
			lineno = defn.Left.Lineno
			Yyerror("%v declared and not used", ln.Sym)
			defn.Left.Used = true // suppress repeats
		} else {
			lineno = ln.Lineno
			Yyerror("%v declared and not used", ln.Sym)
		}
	}

	lineno = lno
	if nerrors != 0 {
		return
	}
	walkstmtlist(Curfn.Nbody.Slice())
	if Debug['W'] != 0 {
		s := fmt.Sprintf("after walk %v", Curfn.Func.Nname.Sym)
		dumplist(s, Curfn.Nbody)
	}

	heapmoves()
	if Debug['W'] != 0 && Curfn.Func.Enter.Len() > 0 {
		s := fmt.Sprintf("enter %v", Curfn.Func.Nname.Sym)
		dumplist(s, Curfn.Func.Enter)
	}
}

func walkstmtlist(s []*Node) {
	for i := range s {
		s[i] = walkstmt(s[i])
	}
}

func samelist(a, b []*Node) bool {
	if len(a) != len(b) {
		return false
	}
	for i, n := range a {
		if n != b[i] {
			return false
		}
	}
	return true
}

func paramoutheap(fn *Node) bool {
	for _, ln := range fn.Func.Dcl {
		switch ln.Class {
		case PPARAMOUT,
			PPARAMOUT | PHEAP:
			return ln.Addrtaken

			// stop early - parameters are over
		case PAUTO,
			PAUTO | PHEAP:
			return false
		}
	}

	return false
}

// adds "adjust" to all the argument locations for the call n.
// n must be a defer or go node that has already been walked.
func adjustargs(n *Node, adjust int) {
	var arg *Node
	var lhs *Node

	callfunc := n.Left
	for _, arg = range callfunc.List.Slice() {
		if arg.Op != OAS {
			Yyerror("call arg not assignment")
		}
		lhs = arg.Left
		if lhs.Op == ONAME {
			// This is a temporary introduced by reorder1.
			// The real store to the stack appears later in the arg list.
			continue
		}

		if lhs.Op != OINDREG {
			Yyerror("call argument store does not use OINDREG")
		}

		// can't really check this in machine-indep code.
		//if(lhs->val.u.reg != D_SP)
		//      yyerror("call arg assign not indreg(SP)");
		lhs.Xoffset += int64(adjust)
	}
}

// The result of walkstmt MUST be assigned back to n, e.g.
// 	n.Left = walkstmt(n.Left)
func walkstmt(n *Node) *Node {
	if n == nil {
		return n
	}
	if n.Dodata == 2 { // don't walk, generated by anylit.
		return n
	}

	setlineno(n)

	walkstmtlist(n.Ninit.Slice())

	switch n.Op {
	default:
		if n.Op == ONAME {
			Yyerror("%v is not a top level statement", n.Sym)
		} else {
			Yyerror("%v is not a top level statement", Oconv(n.Op, 0))
		}
		Dump("nottop", n)

	case OAS,
		OASOP,
		OAS2,
		OAS2DOTTYPE,
		OAS2RECV,
		OAS2FUNC,
		OAS2MAPR,
		OCLOSE,
		OCOPY,
		OCALLMETH,
		OCALLINTER,
		OCALL,
		OCALLFUNC,
		ODELETE,
		OSEND,
		OPRINT,
		OPRINTN,
		OPANIC,
		OEMPTY,
		ORECOVER,
		OGETG:
		if n.Typecheck == 0 {
			Fatalf("missing typecheck: %v", Nconv(n, FmtSign))
		}
		wascopy := n.Op == OCOPY
		init := n.Ninit
		n.Ninit.Set(nil)
		n = walkexpr(n, &init)
		n = addinit(n, init.Slice())
		if wascopy && n.Op == OCONVNOP {
			n.Op = OEMPTY // don't leave plain values as statements.
		}

		// special case for a receive where we throw away
	// the value received.
	case ORECV:
		if n.Typecheck == 0 {
			Fatalf("missing typecheck: %v", Nconv(n, FmtSign))
		}
		init := n.Ninit
		n.Ninit.Set(nil)

		n.Left = walkexpr(n.Left, &init)
		n = mkcall1(chanfn("chanrecv1", 2, n.Left.Type), nil, &init, typename(n.Left.Type), n.Left, nodnil())
		n = walkexpr(n, &init)

		n = addinit(n, init.Slice())

	case OBREAK,
		ODCL,
		OCONTINUE,
		OFALL,
		OGOTO,
		OLABEL,
		ODCLCONST,
		ODCLTYPE,
		OCHECKNIL,
		OVARKILL,
		OVARLIVE:
		break

	case OBLOCK:
		walkstmtlist(n.List.Slice())

	case OXCASE:
		Yyerror("case statement out of place")
		n.Op = OCASE
		fallthrough

	case OCASE:
		n.Right = walkstmt(n.Right)

	case ODEFER:
		hasdefer = true
		switch n.Left.Op {
		case OPRINT, OPRINTN:
			n.Left = walkprintfunc(n.Left, &n.Ninit)

		case OCOPY:
			n.Left = copyany(n.Left, &n.Ninit, true)

		default:
			n.Left = walkexpr(n.Left, &n.Ninit)
		}

		// make room for size & fn arguments.
		adjustargs(n, 2*Widthptr)

	case OFOR:
		if n.Left != nil {
			walkstmtlist(n.Left.Ninit.Slice())
			init := n.Left.Ninit
			n.Left.Ninit.Set(nil)
			n.Left = walkexpr(n.Left, &init)
			n.Left = addinit(n.Left, init.Slice())
		}

		n.Right = walkstmt(n.Right)
		walkstmtlist(n.Nbody.Slice())

	case OIF:
		n.Left = walkexpr(n.Left, &n.Ninit)
		walkstmtlist(n.Nbody.Slice())
		walkstmtlist(n.Rlist.Slice())

	case OPROC:
		switch n.Left.Op {
		case OPRINT, OPRINTN:
			n.Left = walkprintfunc(n.Left, &n.Ninit)

		case OCOPY:
			n.Left = copyany(n.Left, &n.Ninit, true)

		default:
			n.Left = walkexpr(n.Left, &n.Ninit)
		}

		// make room for size & fn arguments.
		adjustargs(n, 2*Widthptr)

	case ORETURN:
		walkexprlist(n.List.Slice(), &n.Ninit)
		if n.List.Len() == 0 {
			break
		}
		if (Curfn.Type.FuncType().Outnamed && n.List.Len() > 1) || paramoutheap(Curfn) {
			// assign to the function out parameters,
			// so that reorder3 can fix up conflicts
			var rl []*Node

			var cl Class
			for _, ln := range Curfn.Func.Dcl {
				cl = ln.Class &^ PHEAP
				if cl == PAUTO {
					break
				}
				if cl == PPARAMOUT {
					rl = append(rl, ln)
				}
			}

			if got, want := n.List.Len(), len(rl); got != want {
				// order should have rewritten multi-value function calls
				// with explicit OAS2FUNC nodes.
				Fatalf("expected %v return arguments, have %v", want, got)
			}

			if samelist(rl, n.List.Slice()) {
				// special return in disguise
				n.List.Set(nil)

				break
			}

			// move function calls out, to make reorder3's job easier.
			walkexprlistsafe(n.List.Slice(), &n.Ninit)

			ll := ascompatee(n.Op, rl, n.List.Slice(), &n.Ninit)
			n.List.Set(reorder3(ll))
			ls := n.List.Slice()
			for i, n := range ls {
				ls[i] = applywritebarrier(n)
			}
			break
		}

		ll := ascompatte(n.Op, nil, false, Curfn.Type.Results(), n.List.Slice(), 1, &n.Ninit)
		n.List.Set(ll)

	case ORETJMP:
		break

	case OSELECT:
		walkselect(n)

	case OSWITCH:
		walkswitch(n)

	case ORANGE:
		walkrange(n)

	case OXFALL:
		Yyerror("fallthrough statement out of place")
		n.Op = OFALL
	}

	if n.Op == ONAME {
		Fatalf("walkstmt ended up with name: %v", Nconv(n, FmtSign))
	}
	return n
}

func isSmallMakeSlice(n *Node) bool {
	if n.Op != OMAKESLICE {
		return false
	}
	l := n.Left
	r := n.Right
	if r == nil {
		r = l
	}
	t := n.Type

	return Smallintconst(l) && Smallintconst(r) && (t.Elem().Width == 0 || r.Int64() < (1<<16)/t.Elem().Width)
}

// walk the whole tree of the body of an
// expression or simple statement.
// the types expressions are calculated.
// compile-time constants are evaluated.
// complex side effects like statements are appended to init
func walkexprlist(s []*Node, init *Nodes) {
	for i := range s {
		s[i] = walkexpr(s[i], init)
	}
}

func walkexprlistsafe(s []*Node, init *Nodes) {
	for i, n := range s {
		s[i] = safeexpr(n, init)
		s[i] = walkexpr(s[i], init)
	}
}

func walkexprlistcheap(s []*Node, init *Nodes) {
	for i, n := range s {
		s[i] = cheapexpr(n, init)
		s[i] = walkexpr(s[i], init)
	}
}

// Build name of function: convI2E etc.
// Not all names are possible
// (e.g., we'll never generate convE2E or convE2I).
func convFuncName(from, to *Type) string {
	tkind := to.iet()
	switch from.iet() {
	case 'I':
		switch tkind {
		case 'E':
			return "convI2E"
		case 'I':
			return "convI2I"
		}
	case 'T':
		switch tkind {
		case 'E':
			return "convT2E"
		case 'I':
			return "convT2I"
		}
	}
	Fatalf("unknown conv func %c2%c", from.iet(), to.iet())
	panic("unreachable")
}

// Build name of function: assertI2E etc.
// If with2suffix is true, the form ending in "2" is returned".
func assertFuncName(from, to *Type, with2suffix bool) string {
	l := len("assertX2X2")
	if !with2suffix {
		l--
	}
	tkind := to.iet()
	switch from.iet() {
	case 'E':
		switch tkind {
		case 'I':
			return "assertE2I2"[:l]
		case 'E':
			return "assertE2E2"[:l]
		case 'T':
			return "assertE2T2"[:l]
		}
	case 'I':
		switch tkind {
		case 'I':
			return "assertI2I2"[:l]
		case 'E':
			return "assertI2E2"[:l]
		case 'T':
			return "assertI2T2"[:l]
		}
	}
	Fatalf("unknown assert func %c2%c", from.iet(), to.iet())
	panic("unreachable")
}

// The result of walkexpr MUST be assigned back to n, e.g.
// 	n.Left = walkexpr(n.Left, init)
func walkexpr(n *Node, init *Nodes) *Node {
	if n == nil {
		return n
	}

	if init == &n.Ninit {
		// not okay to use n->ninit when walking n,
		// because we might replace n with some other node
		// and would lose the init list.
		Fatalf("walkexpr init == &n->ninit")
	}

	if n.Ninit.Len() != 0 {
		walkstmtlist(n.Ninit.Slice())
		init.AppendNodes(&n.Ninit)
	}

	// annoying case - not typechecked
	if n.Op == OKEY {
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)
		return n
	}

	lno := setlineno(n)

	if Debug['w'] > 1 {
		Dump("walk-before", n)
	}

	if n.Typecheck != 1 {
		Fatalf("missed typecheck: %v\n", Nconv(n, FmtSign))
	}

opswitch:
	switch n.Op {
	default:
		Dump("walk", n)
		Fatalf("walkexpr: switch 1 unknown op %v", Nconv(n, FmtShort|FmtSign))

	case OTYPE,
		ONONAME,
		OINDREG,
		OEMPTY,
		OPARAM,
		OGETG:

	case ONOT,
		OMINUS,
		OPLUS,
		OCOM,
		OREAL,
		OIMAG,
		ODOTMETH,
		ODOTINTER:
		n.Left = walkexpr(n.Left, init)

	case OIND:
		n.Left = walkexpr(n.Left, init)

	case ODOT:
		usefield(n)
		n.Left = walkexpr(n.Left, init)

	case ODOTPTR:
		usefield(n)
		if n.Op == ODOTPTR && n.Left.Type.Elem().Width == 0 {
			// No actual copy will be generated, so emit an explicit nil check.
			n.Left = cheapexpr(n.Left, init)

			checknil(n.Left, init)
		}

		n.Left = walkexpr(n.Left, init)

	case OEFACE:
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)

	case OSPTR, OITAB:
		n.Left = walkexpr(n.Left, init)

	case OLEN, OCAP:
		n.Left = walkexpr(n.Left, init)

		// replace len(*[10]int) with 10.
		// delayed until now to preserve side effects.
		t := n.Left.Type

		if t.IsPtr() {
			t = t.Elem()
		}
		if t.IsArray() {
			safeexpr(n.Left, init)
			Nodconst(n, n.Type, t.NumElem())
			n.Typecheck = 1
		}

	case OLSH, ORSH:
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)
		t := n.Left.Type
		n.Bounded = bounded(n.Right, 8*t.Width)
		if Debug['m'] != 0 && n.Etype != 0 && !Isconst(n.Right, CTINT) {
			Warn("shift bounds check elided")
		}

		// Use results from call expression as arguments for complex.
	case OAND,
		OSUB,
		OHMUL,
		OLT,
		OLE,
		OGE,
		OGT,
		OADD,
		OCOMPLEX,
		OLROT:
		if n.Op == OCOMPLEX && n.Left == nil && n.Right == nil {
			n.Left = n.List.First()
			n.Right = n.List.Second()
		}

		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)

	case OOR, OXOR:
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)
		n = walkrotate(n)

	case OEQ, ONE:
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)

		// Disable safemode while compiling this code: the code we
		// generate internally can refer to unsafe.Pointer.
		// In this case it can happen if we need to generate an ==
		// for a struct containing a reflect.Value, which itself has
		// an unexported field of type unsafe.Pointer.
		old_safemode := safemode
		safemode = false
		n = walkcompare(n, init)
		safemode = old_safemode

	case OANDAND, OOROR:
		n.Left = walkexpr(n.Left, init)

		// cannot put side effects from n.Right on init,
		// because they cannot run before n.Left is checked.
		// save elsewhere and store on the eventual n.Right.
		var ll Nodes

		n.Right = walkexpr(n.Right, &ll)
		n.Right = addinit(n.Right, ll.Slice())

	case OPRINT, OPRINTN:
		walkexprlist(n.List.Slice(), init)
		n = walkprint(n, init)

	case OPANIC:
		n = mkcall("gopanic", nil, init, n.Left)

	case ORECOVER:
		n = mkcall("gorecover", n.Type, init, Nod(OADDR, nodfp, nil))

	case OLITERAL:
		n.Addable = true

	case OCLOSUREVAR, OCFUNC:
		n.Addable = true

	case ONAME:
		if n.Class&PHEAP == 0 && n.Class != PPARAMREF {
			n.Addable = true
		}

	case OCALLINTER:
		usemethod(n)
		t := n.Left.Type
		if n.List.Len() != 0 && n.List.First().Op == OAS {
			break
		}
		n.Left = walkexpr(n.Left, init)
		walkexprlist(n.List.Slice(), init)
		ll := ascompatte(n.Op, n, n.Isddd, t.Params(), n.List.Slice(), 0, init)
		n.List.Set(reorder1(ll))

	case OCALLFUNC:
		if n.Left.Op == OCLOSURE {
			// Transform direct call of a closure to call of a normal function.
			// transformclosure already did all preparation work.

			// Prepend captured variables to argument list.
			n.List.Set(append(n.Left.Func.Enter.Slice(), n.List.Slice()...))

			n.Left.Func.Enter.Set(nil)

			// Replace OCLOSURE with ONAME/PFUNC.
			n.Left = n.Left.Func.Closure.Func.Nname

			// Update type of OCALLFUNC node.
			// Output arguments had not changed, but their offsets could.
			if n.Left.Type.Results().NumFields() == 1 {
				n.Type = n.Left.Type.Results().Field(0).Type
			} else {
				n.Type = n.Left.Type.Results()
			}
		}

		t := n.Left.Type
		if n.List.Len() != 0 && n.List.First().Op == OAS {
			break
		}

		n.Left = walkexpr(n.Left, init)
		walkexprlist(n.List.Slice(), init)

		if n.Left.Op == ONAME && n.Left.Sym.Name == "Sqrt" && n.Left.Sym.Pkg.Path == "math" {
			if Thearch.LinkArch.InFamily(sys.AMD64, sys.ARM, sys.ARM64, sys.PPC64, sys.S390X) {
				n.Op = OSQRT
				n.Left = n.List.First()
				n.List.Set(nil)
				break opswitch
			}
		}

		ll := ascompatte(n.Op, n, n.Isddd, t.Params(), n.List.Slice(), 0, init)
		n.List.Set(reorder1(ll))

	case OCALLMETH:
		t := n.Left.Type
		if n.List.Len() != 0 && n.List.First().Op == OAS {
			break
		}
		n.Left = walkexpr(n.Left, init)
		walkexprlist(n.List.Slice(), init)
		ll := ascompatte(n.Op, n, false, t.Recvs(), []*Node{n.Left.Left}, 0, init)
		lr := ascompatte(n.Op, n, n.Isddd, t.Params(), n.List.Slice(), 0, init)
		ll = append(ll, lr...)
		n.Left.Left = nil
		ullmancalc(n.Left)
		n.List.Set(reorder1(ll))

	case OAS:
		init.AppendNodes(&n.Ninit)

		n.Left = walkexpr(n.Left, init)
		n.Left = safeexpr(n.Left, init)

		if oaslit(n, init) {
			break
		}

		if n.Right == nil || iszero(n.Right) && !instrumenting {
			break
		}

		switch n.Right.Op {
		default:
			n.Right = walkexpr(n.Right, init)

		case ODOTTYPE:
			// TODO(rsc): The Isfat is for consistency with componentgen and orderexpr.
			// It needs to be removed in all three places.
			// That would allow inlining x.(struct{*int}) the same as x.(*int).
			if isdirectiface(n.Right.Type) && !Isfat(n.Right.Type) && !instrumenting {
				// handled directly during cgen
				n.Right = walkexpr(n.Right, init)
				break
			}

			// x = i.(T); n.Left is x, n.Right.Left is i.
			// orderstmt made sure x is addressable.
			n.Right.Left = walkexpr(n.Right.Left, init)

			n1 := Nod(OADDR, n.Left, nil)
			r := n.Right // i.(T)

			if Debug_typeassert > 0 {
				Warn("type assertion not inlined")
			}

			fn := syslook(assertFuncName(r.Left.Type, r.Type, false))
			fn = substArgTypes(fn, r.Left.Type, r.Type)

			n = mkcall1(fn, nil, init, typename(r.Type), r.Left, n1)
			n = walkexpr(n, init)
			break opswitch

		case ORECV:
			// x = <-c; n.Left is x, n.Right.Left is c.
			// orderstmt made sure x is addressable.
			n.Right.Left = walkexpr(n.Right.Left, init)

			n1 := Nod(OADDR, n.Left, nil)
			r := n.Right.Left // the channel
			n = mkcall1(chanfn("chanrecv1", 2, r.Type), nil, init, typename(r.Type), r, n1)
			n = walkexpr(n, init)
			break opswitch

		case OAPPEND:
			// x = append(...)
			r := n.Right
			if r.Isddd {
				r = appendslice(r, init) // also works for append(slice, string).
			} else {
				r = walkappend(r, init, n)
			}
			n.Right = r
			if r.Op == OAPPEND {
				// Left in place for back end.
				// Do not add a new write barrier.
				break opswitch
			}
			// Otherwise, lowered for race detector.
			// Treat as ordinary assignment.
		}

		if n.Left != nil && n.Right != nil {
			dd := n.Dodata
			n = convas(n, init)
			n.Dodata = dd
			n = applywritebarrier(n)
		}

	case OAS2:
		init.AppendNodes(&n.Ninit)
		walkexprlistsafe(n.List.Slice(), init)
		walkexprlistsafe(n.Rlist.Slice(), init)
		ll := ascompatee(OAS, n.List.Slice(), n.Rlist.Slice(), init)
		ll = reorder3(ll)
		for i, n := range ll {
			ll[i] = applywritebarrier(n)
		}
		n = liststmt(ll)

		// a,b,... = fn()
	case OAS2FUNC:
		init.AppendNodes(&n.Ninit)

		r := n.Rlist.First()
		walkexprlistsafe(n.List.Slice(), init)
		r = walkexpr(r, init)

		ll := ascompatet(n.Op, n.List, r.Type, 0, init)
		for i, n := range ll {
			ll[i] = applywritebarrier(n)
		}
		n = liststmt(append([]*Node{r}, ll...))

		// x, y = <-c
	// orderstmt made sure x is addressable.
	case OAS2RECV:
		init.AppendNodes(&n.Ninit)

		r := n.Rlist.First()
		walkexprlistsafe(n.List.Slice(), init)
		r.Left = walkexpr(r.Left, init)
		var n1 *Node
		if isblank(n.List.First()) {
			n1 = nodnil()
		} else {
			n1 = Nod(OADDR, n.List.First(), nil)
		}
		n1.Etype = 1 // addr does not escape
		fn := chanfn("chanrecv2", 2, r.Left.Type)
		r = mkcall1(fn, n.List.Second().Type, init, typename(r.Left.Type), r.Left, n1)
		n = Nod(OAS, n.List.Second(), r)
		n = typecheck(n, Etop)

		// a,b = m[i];
	case OAS2MAPR:
		init.AppendNodes(&n.Ninit)

		r := n.Rlist.First()
		walkexprlistsafe(n.List.Slice(), init)
		r.Left = walkexpr(r.Left, init)
		r.Right = walkexpr(r.Right, init)
		t := r.Left.Type
		p := ""
		if t.Val().Width <= 128 { // Check ../../runtime/hashmap.go:maxValueSize before changing.
			switch algtype(t.Key()) {
			case AMEM32:
				p = "mapaccess2_fast32"
			case AMEM64:
				p = "mapaccess2_fast64"
			case ASTRING:
				p = "mapaccess2_faststr"
			}
		}

		var key *Node
		if p != "" {
			// fast versions take key by value
			key = r.Right
		} else {
			// standard version takes key by reference
			// orderexpr made sure key is addressable.
			key = Nod(OADDR, r.Right, nil)

			p = "mapaccess2"
		}

		// from:
		//   a,b = m[i]
		// to:
		//   var,b = mapaccess2*(t, m, i)
		//   a = *var
		a := n.List.First()

		if w := t.Val().Width; w <= 1024 { // 1024 must match ../../../../runtime/hashmap.go:maxZero
			fn := mapfn(p, t)
			r = mkcall1(fn, fn.Type.Results(), init, typename(t), r.Left, key)
		} else {
			fn := mapfn("mapaccess2_fat", t)
			z := zeroaddr(w)
			r = mkcall1(fn, fn.Type.Results(), init, typename(t), r.Left, key, z)
		}

		// mapaccess2* returns a typed bool, but due to spec changes,
		// the boolean result of i.(T) is now untyped so we make it the
		// same type as the variable on the lhs.
		if !isblank(n.List.Second()) {
			r.Type.Field(1).Type = n.List.Second().Type
		}
		n.Rlist.Set1(r)
		n.Op = OAS2FUNC

		// don't generate a = *var if a is _
		if !isblank(a) {
			var_ := temp(Ptrto(t.Val()))
			var_.Typecheck = 1
			var_.NonNil = true // mapaccess always returns a non-nil pointer
			n.List.SetIndex(0, var_)
			n = walkexpr(n, init)
			init.Append(n)
			n = Nod(OAS, a, Nod(OIND, var_, nil))
		}

		n = typecheck(n, Etop)
		n = walkexpr(n, init)

	case ODELETE:
		init.AppendNodes(&n.Ninit)
		map_ := n.List.First()
		key := n.List.Second()
		map_ = walkexpr(map_, init)
		key = walkexpr(key, init)

		// orderstmt made sure key is addressable.
		key = Nod(OADDR, key, nil)

		t := map_.Type
		n = mkcall1(mapfndel("mapdelete", t), nil, init, typename(t), map_, key)

	case OAS2DOTTYPE:
		e := n.Rlist.First() // i.(T)
		// TODO(rsc): The Isfat is for consistency with componentgen and orderexpr.
		// It needs to be removed in all three places.
		// That would allow inlining x.(struct{*int}) the same as x.(*int).
		if isdirectiface(e.Type) && !Isfat(e.Type) && !instrumenting {
			// handled directly during gen.
			walkexprlistsafe(n.List.Slice(), init)
			e.Left = walkexpr(e.Left, init)
			break
		}

		// res, ok = i.(T)
		// orderstmt made sure a is addressable.
		init.AppendNodes(&n.Ninit)

		walkexprlistsafe(n.List.Slice(), init)
		e.Left = walkexpr(e.Left, init)
		t := e.Type    // T
		from := e.Left // i

		oktype := Types[TBOOL]
		ok := n.List.Second()
		if !isblank(ok) {
			oktype = ok.Type
		}

		fromKind := from.Type.iet()
		toKind := t.iet()

		// Avoid runtime calls in a few cases of the form _, ok := i.(T).
		// This is faster and shorter and allows the corresponding assertX2X2
		// routines to skip nil checks on their last argument.
		if isblank(n.List.First()) {
			var fast *Node
			switch {
			case fromKind == 'E' && toKind == 'T':
				tab := Nod(OITAB, from, nil) // type:eface::tab:iface
				typ := Nod(OCONVNOP, typename(t), nil)
				typ.Type = Ptrto(Types[TUINTPTR])
				fast = Nod(OEQ, tab, typ)
			case fromKind == 'I' && toKind == 'E',
				fromKind == 'E' && toKind == 'E':
				tab := Nod(OITAB, from, nil)
				fast = Nod(ONE, nodnil(), tab)
			}
			if fast != nil {
				if Debug_typeassert > 0 {
					Warn("type assertion (ok only) inlined")
				}
				n = Nod(OAS, ok, fast)
				n = typecheck(n, Etop)
				break
			}
		}

		var resptr *Node // &res
		if isblank(n.List.First()) {
			resptr = nodnil()
		} else {
			resptr = Nod(OADDR, n.List.First(), nil)
		}
		resptr.Etype = 1 // addr does not escape

		if Debug_typeassert > 0 {
			Warn("type assertion not inlined")
		}
		fn := syslook(assertFuncName(from.Type, t, true))
		fn = substArgTypes(fn, from.Type, t)
		call := mkcall1(fn, oktype, init, typename(t), from, resptr)
		n = Nod(OAS, ok, call)
		n = typecheck(n, Etop)

	case ODOTTYPE, ODOTTYPE2:
		if !isdirectiface(n.Type) || Isfat(n.Type) {
			Fatalf("walkexpr ODOTTYPE") // should see inside OAS only
		}
		n.Left = walkexpr(n.Left, init)

	case OCONVIFACE:
		n.Left = walkexpr(n.Left, init)

		// Optimize convT2E or convT2I as a two-word copy when T is pointer-shaped.
		if isdirectiface(n.Left.Type) {
			var t *Node
			if n.Type.IsEmptyInterface() {
				t = typename(n.Left.Type)
			} else {
				t = itabname(n.Left.Type, n.Type)
			}
			l := Nod(OEFACE, t, n.Left)
			l.Type = n.Type
			l.Typecheck = n.Typecheck
			n = l
			break
		}

		var ll []*Node
		if n.Type.IsEmptyInterface() {
			if !n.Left.Type.IsInterface() {
				ll = append(ll, typename(n.Left.Type))
			}
		} else {
			if n.Left.Type.IsInterface() {
				ll = append(ll, typename(n.Type))
			} else {
				ll = append(ll, itabname(n.Left.Type, n.Type))
			}
		}

		if n.Left.Type.IsInterface() {
			ll = append(ll, n.Left)
		} else {
			// regular types are passed by reference to avoid C vararg calls
			// orderexpr arranged for n.Left to be a temporary for all
			// the conversions it could see. comparison of an interface
			// with a non-interface, especially in a switch on interface value
			// with non-interface cases, is not visible to orderstmt, so we
			// have to fall back on allocating a temp here.
			if islvalue(n.Left) {
				ll = append(ll, Nod(OADDR, n.Left, nil))
			} else {
				ll = append(ll, Nod(OADDR, copyexpr(n.Left, n.Left.Type, init), nil))
			}
			dowidth(n.Left.Type)
			r := nodnil()
			if n.Esc == EscNone && n.Left.Type.Width <= 1024 {
				// Allocate stack buffer for value stored in interface.
				r = temp(n.Left.Type)
				r = Nod(OAS, r, nil) // zero temp
				r = typecheck(r, Etop)
				init.Append(r)
				r = Nod(OADDR, r.Left, nil)
				r = typecheck(r, Erv)
			}
			ll = append(ll, r)
		}

		fn := syslook(convFuncName(n.Left.Type, n.Type))
		if !n.Left.Type.IsInterface() {
			fn = substArgTypes(fn, n.Left.Type, n.Left.Type, n.Type)
		} else {
			fn = substArgTypes(fn, n.Left.Type, n.Type)
		}
		dowidth(fn.Type)
		n = Nod(OCALL, fn, nil)
		n.List.Set(ll)
		n = typecheck(n, Erv)
		n = walkexpr(n, init)

	case OCONV, OCONVNOP:
		if Thearch.LinkArch.Family == sys.ARM {
			if n.Left.Type.IsFloat() {
				if n.Type.Etype == TINT64 {
					n = mkcall("float64toint64", n.Type, init, conv(n.Left, Types[TFLOAT64]))
					break
				}

				if n.Type.Etype == TUINT64 {
					n = mkcall("float64touint64", n.Type, init, conv(n.Left, Types[TFLOAT64]))
					break
				}
			}

			if n.Type.IsFloat() {
				if n.Left.Type.Etype == TINT64 {
					n = mkcall("int64tofloat64", n.Type, init, conv(n.Left, Types[TINT64]))
					break
				}

				if n.Left.Type.Etype == TUINT64 {
					n = mkcall("uint64tofloat64", n.Type, init, conv(n.Left, Types[TUINT64]))
					break
				}
			}
		}

		n.Left = walkexpr(n.Left, init)

	case OANDNOT:
		n.Left = walkexpr(n.Left, init)
		n.Op = OAND
		n.Right = Nod(OCOM, n.Right, nil)
		n.Right = typecheck(n.Right, Erv)
		n.Right = walkexpr(n.Right, init)

	case OMUL:
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)
		n = walkmul(n, init)

	case ODIV, OMOD:
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)

		// rewrite complex div into function call.
		et := n.Left.Type.Etype

		if Iscomplex[et] && n.Op == ODIV {
			t := n.Type
			n = mkcall("complex128div", Types[TCOMPLEX128], init, conv(n.Left, Types[TCOMPLEX128]), conv(n.Right, Types[TCOMPLEX128]))
			n = conv(n, t)
			break
		}

		// Nothing to do for float divisions.
		if Isfloat[et] {
			break
		}

		// Try rewriting as shifts or magic multiplies.
		n = walkdiv(n, init)

		// rewrite 64-bit div and mod into function calls
		// on 32-bit architectures.
		switch n.Op {
		case OMOD, ODIV:
			if Widthreg >= 8 || (et != TUINT64 && et != TINT64) {
				break opswitch
			}
			var fn string
			if et == TINT64 {
				fn = "int64"
			} else {
				fn = "uint64"
			}
			if n.Op == ODIV {
				fn += "div"
			} else {
				fn += "mod"
			}
			n = mkcall(fn, n.Type, init, conv(n.Left, Types[et]), conv(n.Right, Types[et]))
		}

	case OINDEX:
		n.Left = walkexpr(n.Left, init)

		// save the original node for bounds checking elision.
		// If it was a ODIV/OMOD walk might rewrite it.
		r := n.Right

		n.Right = walkexpr(n.Right, init)

		// if range of type cannot exceed static array bound,
		// disable bounds check.
		if n.Bounded {
			break
		}
		t := n.Left.Type
		if t != nil && t.IsPtr() {
			t = t.Elem()
		}
		if t.IsArray() {
			n.Bounded = bounded(r, t.NumElem())
			if Debug['m'] != 0 && n.Bounded && !Isconst(n.Right, CTINT) {
				Warn("index bounds check elided")
			}
			if Smallintconst(n.Right) && !n.Bounded {
				Yyerror("index out of bounds")
			}
		} else if Isconst(n.Left, CTSTR) {
			n.Bounded = bounded(r, int64(len(n.Left.Val().U.(string))))
			if Debug['m'] != 0 && n.Bounded && !Isconst(n.Right, CTINT) {
				Warn("index bounds check elided")
			}
			if Smallintconst(n.Right) {
				if !n.Bounded {
					Yyerror("index out of bounds")
				} else {
					// replace "abc"[1] with 'b'.
					// delayed until now because "abc"[1] is not
					// an ideal constant.
					v := n.Right.Int64()

					Nodconst(n, n.Type, int64(n.Left.Val().U.(string)[v]))
					n.Typecheck = 1
				}
			}
		}

		if Isconst(n.Right, CTINT) {
			if n.Right.Val().U.(*Mpint).CmpInt64(0) < 0 || n.Right.Val().U.(*Mpint).Cmp(Maxintval[TINT]) > 0 {
				Yyerror("index out of bounds")
			}
		}

	case OINDEXMAP:
		if n.Etype == 1 {
			break
		}
		n.Left = walkexpr(n.Left, init)
		n.Right = walkexpr(n.Right, init)

		t := n.Left.Type
		p := ""
		if t.Val().Width <= 128 { // Check ../../runtime/hashmap.go:maxValueSize before changing.
			switch algtype(t.Key()) {
			case AMEM32:
				p = "mapaccess1_fast32"
			case AMEM64:
				p = "mapaccess1_fast64"
			case ASTRING:
				p = "mapaccess1_faststr"
			}
		}

		var key *Node
		if p != "" {
			// fast versions take key by value
			key = n.Right
		} else {
			// standard version takes key by reference.
			// orderexpr made sure key is addressable.
			key = Nod(OADDR, n.Right, nil)
			p = "mapaccess1"
		}

		if w := t.Val().Width; w <= 1024 { // 1024 must match ../../../../runtime/hashmap.go:maxZero
			n = mkcall1(mapfn(p, t), Ptrto(t.Val()), init, typename(t), n.Left, key)
		} else {
			p = "mapaccess1_fat"
			z := zeroaddr(w)
			n = mkcall1(mapfn(p, t), Ptrto(t.Val()), init, typename(t), n.Left, key, z)
		}
		n.NonNil = true // mapaccess always returns a non-nil pointer
		n = Nod(OIND, n, nil)
		n.Type = t.Val()
		n.Typecheck = 1

	case ORECV:
		Fatalf("walkexpr ORECV") // should see inside OAS only

	case OSLICE, OSLICEARR, OSLICESTR:
		n.Left = walkexpr(n.Left, init)
		n.Right.Left = walkexpr(n.Right.Left, init)
		if n.Right.Left != nil && iszero(n.Right.Left) {
			// Reduce x[0:j] to x[:j].
			n.Right.Left = nil
		}
		n.Right.Right = walkexpr(n.Right.Right, init)
		n = reduceSlice(n)

	case OSLICE3, OSLICE3ARR:
		n.Left = walkexpr(n.Left, init)
		n.Right.Left = walkexpr(n.Right.Left, init)
		if n.Right.Left != nil && iszero(n.Right.Left) {
			// Reduce x[0:j:k] to x[:j:k].
			n.Right.Left = nil
		}
		n.Right.Right.Left = walkexpr(n.Right.Right.Left, init)
		n.Right.Right.Right = walkexpr(n.Right.Right.Right, init)

		r := n.Right.Right.Right
		if r != nil && r.Op == OCAP && samesafeexpr(n.Left, r.Left) {
			// Reduce x[i:j:cap(x)] to x[i:j].
			n.Right.Right = n.Right.Right.Left
			if n.Op == OSLICE3 {
				n.Op = OSLICE
			} else {
				n.Op = OSLICEARR
			}
			n = reduceSlice(n)
		}

	case OADDR:
		n.Left = walkexpr(n.Left, init)

	case ONEW:
		if n.Esc == EscNone {
			if n.Type.Elem().Width >= 1<<16 {
				Fatalf("large ONEW with EscNone: %v", n)
			}
			r := temp(n.Type.Elem())
			r = Nod(OAS, r, nil) // zero temp
			r = typecheck(r, Etop)
			init.Append(r)
			r = Nod(OADDR, r.Left, nil)
			r = typecheck(r, Erv)
			n = r
		} else {
			n = callnew(n.Type.Elem())
		}

		// If one argument to the comparison is an empty string,
	// comparing the lengths instead will yield the same result
	// without the function call.
	case OCMPSTR:
		if (Isconst(n.Left, CTSTR) && len(n.Left.Val().U.(string)) == 0) || (Isconst(n.Right, CTSTR) && len(n.Right.Val().U.(string)) == 0) {
			// TODO(marvin): Fix Node.EType type union.
			r := Nod(Op(n.Etype), Nod(OLEN, n.Left, nil), Nod(OLEN, n.Right, nil))
			r = typecheck(r, Erv)
			r = walkexpr(r, init)
			r.Type = n.Type
			n = r
			break
		}

		// s + "badgerbadgerbadger" == "badgerbadgerbadger"
		if (Op(n.Etype) == OEQ || Op(n.Etype) == ONE) && Isconst(n.Right, CTSTR) && n.Left.Op == OADDSTR && n.Left.List.Len() == 2 && Isconst(n.Left.List.Second(), CTSTR) && strlit(n.Right) == strlit(n.Left.List.Second()) {
			// TODO(marvin): Fix Node.EType type union.
			r := Nod(Op(n.Etype), Nod(OLEN, n.Left.List.First(), nil), Nodintconst(0))
			r = typecheck(r, Erv)
			r = walkexpr(r, init)
			r.Type = n.Type
			n = r
			break
		}

		var r *Node
		// TODO(marvin): Fix Node.EType type union.
		if Op(n.Etype) == OEQ || Op(n.Etype) == ONE {
			// prepare for rewrite below
			n.Left = cheapexpr(n.Left, init)

			n.Right = cheapexpr(n.Right, init)

			r = mkcall("eqstring", Types[TBOOL], init, conv(n.Left, Types[TSTRING]), conv(n.Right, Types[TSTRING]))

			// quick check of len before full compare for == or !=
			// eqstring assumes that the lengths are equal
			// TODO(marvin): Fix Node.EType type union.
			if Op(n.Etype) == OEQ {
				// len(left) == len(right) && eqstring(left, right)
				r = Nod(OANDAND, Nod(OEQ, Nod(OLEN, n.Left, nil), Nod(OLEN, n.Right, nil)), r)
			} else {
				// len(left) != len(right) || !eqstring(left, right)
				r = Nod(ONOT, r, nil)

				r = Nod(OOROR, Nod(ONE, Nod(OLEN, n.Left, nil), Nod(OLEN, n.Right, nil)), r)
			}

			r = typecheck(r, Erv)
			r = walkexpr(r, nil)
		} else {
			// sys_cmpstring(s1, s2) :: 0
			r = mkcall("cmpstring", Types[TINT], init, conv(n.Left, Types[TSTRING]), conv(n.Right, Types[TSTRING]))

			// TODO(marvin): Fix Node.EType type union.
			r = Nod(Op(n.Etype), r, Nodintconst(0))
		}

		r = typecheck(r, Erv)
		if !n.Type.IsBoolean() {
			Fatalf("cmp %v", n.Type)
		}
		r.Type = n.Type
		n = r

	case OADDSTR:
		n = addstr(n, init)

	case OAPPEND:
		// order should make sure we only see OAS(node, OAPPEND), which we handle above.
		Fatalf("append outside assignment")

	case OCOPY:
		n = copyany(n, init, instrumenting)

		// cannot use chanfn - closechan takes any, not chan any
	case OCLOSE:
		fn := syslook("closechan")

		fn = substArgTypes(fn, n.Left.Type)
		n = mkcall1(fn, nil, init, n.Left)

	case OMAKECHAN:
		n = mkcall1(chanfn("makechan", 1, n.Type), n.Type, init, typename(n.Type), conv(n.Left, Types[TINT64]))

	case OMAKEMAP:
		t := n.Type

		a := nodnil() // hmap buffer
		r := nodnil() // bucket buffer
		if n.Esc == EscNone {
			// Allocate hmap buffer on stack.
			var_ := temp(hmap(t))

			a = Nod(OAS, var_, nil) // zero temp
			a = typecheck(a, Etop)
			init.Append(a)
			a = Nod(OADDR, var_, nil)

			// Allocate one bucket on stack.
			// Maximum key/value size is 128 bytes, larger objects
			// are stored with an indirection. So max bucket size is 2048+eps.
			var_ = temp(mapbucket(t))

			r = Nod(OAS, var_, nil) // zero temp
			r = typecheck(r, Etop)
			init.Append(r)
			r = Nod(OADDR, var_, nil)
		}

		fn := syslook("makemap")
		fn = substArgTypes(fn, hmap(t), mapbucket(t), t.Key(), t.Val())
		n = mkcall1(fn, n.Type, init, typename(n.Type), conv(n.Left, Types[TINT64]), a, r)

	case OMAKESLICE:
		l := n.Left
		r := n.Right
		if r == nil {
			r = safeexpr(l, init)
			l = r
		}
		t := n.Type
		if n.Esc == EscNone {
			if !isSmallMakeSlice(n) {
				Fatalf("non-small OMAKESLICE with EscNone: %v", n)
			}
			// var arr [r]T
			// n = arr[:l]
			t = aindex(r, t.Elem()) // [r]T
			var_ := temp(t)
			a := Nod(OAS, var_, nil) // zero temp
			a = typecheck(a, Etop)
			init.Append(a)
			r := Nod(OSLICE, var_, Nod(OKEY, nil, l)) // arr[:l]
			r = conv(r, n.Type)                       // in case n.Type is named.
			r = typecheck(r, Erv)
			r = walkexpr(r, init)
			n = r
		} else {
			// makeslice(et *Type, nel int64, max int64) (ary []any)
			fn := syslook("makeslice")

			fn = substArgTypes(fn, t.Elem()) // any-1
			n = mkcall1(fn, n.Type, init, typename(t.Elem()), conv(l, Types[TINT64]), conv(r, Types[TINT64]))
		}

	case ORUNESTR:
		a := nodnil()
		if n.Esc == EscNone {
			t := aindex(Nodintconst(4), Types[TUINT8])
			var_ := temp(t)
			a = Nod(OADDR, var_, nil)
		}

		// intstring(*[4]byte, rune)
		n = mkcall("intstring", n.Type, init, a, conv(n.Left, Types[TINT64]))

	case OARRAYBYTESTR:
		a := nodnil()
		if n.Esc == EscNone {
			// Create temporary buffer for string on stack.
			t := aindex(Nodintconst(tmpstringbufsize), Types[TUINT8])

			a = Nod(OADDR, temp(t), nil)
		}

		// slicebytetostring(*[32]byte, []byte) string;
		n = mkcall("slicebytetostring", n.Type, init, a, n.Left)

		// slicebytetostringtmp([]byte) string;
	case OARRAYBYTESTRTMP:
		n = mkcall("slicebytetostringtmp", n.Type, init, n.Left)

		// slicerunetostring(*[32]byte, []rune) string;
	case OARRAYRUNESTR:
		a := nodnil()

		if n.Esc == EscNone {
			// Create temporary buffer for string on stack.
			t := aindex(Nodintconst(tmpstringbufsize), Types[TUINT8])

			a = Nod(OADDR, temp(t), nil)
		}

		n = mkcall("slicerunetostring", n.Type, init, a, n.Left)

		// stringtoslicebyte(*32[byte], string) []byte;
	case OSTRARRAYBYTE:
		a := nodnil()

		if n.Esc == EscNone {
			// Create temporary buffer for slice on stack.
			t := aindex(Nodintconst(tmpstringbufsize), Types[TUINT8])

			a = Nod(OADDR, temp(t), nil)
		}

		n = mkcall("stringtoslicebyte", n.Type, init, a, conv(n.Left, Types[TSTRING]))

		// stringtoslicebytetmp(string) []byte;
	case OSTRARRAYBYTETMP:
		n = mkcall("stringtoslicebytetmp", n.Type, init, conv(n.Left, Types[TSTRING]))

		// stringtoslicerune(*[32]rune, string) []rune
	case OSTRARRAYRUNE:
		a := nodnil()

		if n.Esc == EscNone {
			// Create temporary buffer for slice on stack.
			t := aindex(Nodintconst(tmpstringbufsize), Types[TINT32])

			a = Nod(OADDR, temp(t), nil)
		}

		n = mkcall("stringtoslicerune", n.Type, init, a, n.Left)

		// ifaceeq(i1 any-1, i2 any-2) (ret bool);
	case OCMPIFACE:
		if !Eqtype(n.Left.Type, n.Right.Type) {
			Fatalf("ifaceeq %v %v %v", Oconv(n.Op, 0), n.Left.Type, n.Right.Type)
		}
		var fn *Node
		if n.Left.Type.IsEmptyInterface() {
			fn = syslook("efaceeq")
		} else {
			fn = syslook("ifaceeq")
		}

		n.Right = cheapexpr(n.Right, init)
		n.Left = cheapexpr(n.Left, init)
		fn = substArgTypes(fn, n.Right.Type, n.Left.Type)
		r := mkcall1(fn, n.Type, init, n.Left, n.Right)
		// TODO(marvin): Fix Node.EType type union.
		if Op(n.Etype) == ONE {
			r = Nod(ONOT, r, nil)
		}

		// check itable/type before full compare.
		// TODO(marvin): Fix Node.EType type union.
		if Op(n.Etype) == OEQ {
			r = Nod(OANDAND, Nod(OEQ, Nod(OITAB, n.Left, nil), Nod(OITAB, n.Right, nil)), r)
		} else {
			r = Nod(OOROR, Nod(ONE, Nod(OITAB, n.Left, nil), Nod(OITAB, n.Right, nil)), r)
		}
		r = typecheck(r, Erv)
		r = walkexpr(r, init)
		r.Type = n.Type
		n = r

	case OARRAYLIT, OMAPLIT, OSTRUCTLIT, OPTRLIT:
		if isStaticCompositeLiteral(n) {
			// n can be directly represented in the read-only data section.
			// Make direct reference to the static data. See issue 12841.
			vstat := staticname(n.Type, 0)
			if n.Op == OSTRUCTLIT {
				structlit(0, 1, n, vstat, init)
			} else {
				arraylit(0, 1, n, vstat, init)
			}
			n = vstat
			n = typecheck(n, Erv)
			break
		}
		var_ := temp(n.Type)
		anylit(0, n, var_, init)
		n = var_

	case OSEND:
		n1 := n.Right
		n1 = assignconv(n1, n.Left.Type.Elem(), "chan send")
		n1 = walkexpr(n1, init)
		n1 = Nod(OADDR, n1, nil)
		n = mkcall1(chanfn("chansend1", 2, n.Left.Type), nil, init, typename(n.Left.Type), n.Left, n1)

	case OCLOSURE:
		n = walkclosure(n, init)

	case OCALLPART:
		n = walkpartialcall(n, init)
	}

	// Expressions that are constant at run time but not
	// considered const by the language spec are not turned into
	// constants until walk. For example, if n is y%1 == 0, the
	// walk of y%1 may have replaced it by 0.
	// Check whether n with its updated args is itself now a constant.
	t := n.Type

	evconst(n)
	n.Type = t
	if n.Op == OLITERAL {
		n = typecheck(n, Erv)
	}

	ullmancalc(n)

	if Debug['w'] != 0 && n != nil {
		Dump("walk", n)
	}

	lineno = lno
	return n
}

func reduceSlice(n *Node) *Node {
	r := n.Right.Right
	if r != nil && r.Op == OLEN && samesafeexpr(n.Left, r.Left) {
		// Reduce x[i:len(x)] to x[i:].
		n.Right.Right = nil
	}
	if (n.Op == OSLICE || n.Op == OSLICESTR) && n.Right.Left == nil && n.Right.Right == nil {
		// Reduce x[:] to x.
		if Debug_slice > 0 {
			Warn("slice: omit slice operation")
		}
		return n.Left
	}
	return n
}

func ascompatee1(op Op, l *Node, r *Node, init *Nodes) *Node {
	// convas will turn map assigns into function calls,
	// making it impossible for reorder3 to work.
	n := Nod(OAS, l, r)

	if l.Op == OINDEXMAP {
		return n
	}

	return convas(n, init)
}

func ascompatee(op Op, nl, nr []*Node, init *Nodes) []*Node {
	// check assign expression list to
	// a expression list. called in
	//	expr-list = expr-list

	// ensure order of evaluation for function calls
	for i := range nl {
		nl[i] = safeexpr(nl[i], init)
	}
	for i1 := range nr {
		nr[i1] = safeexpr(nr[i1], init)
	}

	var nn []*Node
	i := 0
	for ; i < len(nl); i++ {
		if i >= len(nr) {
			break
		}
		// Do not generate 'x = x' during return. See issue 4014.
		if op == ORETURN && nl[i] == nr[i] {
			continue
		}
		nn = append(nn, ascompatee1(op, nl[i], nr[i], init))
	}

	// cannot happen: caller checked that lists had same length
	if i < len(nl) || i < len(nr) {
		var nln, nrn Nodes
		nln.Set(nl)
		nrn.Set(nr)
		Yyerror("error in shape across %v %v %v / %d %d [%s]", Hconv(nln, FmtSign), Oconv(op, 0), Hconv(nrn, FmtSign), len(nl), len(nr), Curfn.Func.Nname.Sym.Name)
	}
	return nn
}

// l is an lv and rt is the type of an rv
// return 1 if this implies a function call
// evaluating the lv or a function call
// in the conversion of the types
func fncall(l *Node, rt *Type) bool {
	if l.Ullman >= UINF || l.Op == OINDEXMAP {
		return true
	}
	var r Node
	if needwritebarrier(l, &r) {
		return true
	}
	if Eqtype(l.Type, rt) {
		return false
	}
	return true
}

// check assign type list to
// a expression list. called in
//	expr-list = func()
func ascompatet(op Op, nl Nodes, nr *Type, fp int, init *Nodes) []*Node {
	r, saver := IterFields(nr)

	var nn, mm []*Node
	var ullmanOverflow bool
	var i int
	for i = 0; i < nl.Len(); i++ {
		if r == nil {
			break
		}
		l := nl.Index(i)
		if isblank(l) {
			r = saver.Next()
			continue
		}

		// any lv that causes a fn call must be
		// deferred until all the return arguments
		// have been pulled from the output arguments
		if fncall(l, r.Type) {
			tmp := temp(r.Type)
			tmp = typecheck(tmp, Erv)
			a := Nod(OAS, l, tmp)
			a = convas(a, init)
			mm = append(mm, a)
			l = tmp
		}

		a := Nod(OAS, l, nodarg(r, fp))
		a = convas(a, init)
		ullmancalc(a)
		if a.Ullman >= UINF {
			Dump("ascompatet ucount", a)
			ullmanOverflow = true
		}

		nn = append(nn, a)
		r = saver.Next()
	}

	if i < nl.Len() || r != nil {
		Yyerror("ascompatet: assignment count mismatch: %d = %d", nl.Len(), nr.NumFields())
	}

	if ullmanOverflow {
		Fatalf("ascompatet: too many function calls evaluating parameters")
	}
	return append(nn, mm...)
}

// package all the arguments that match a ... T parameter into a []T.
func mkdotargslice(lr0, nn []*Node, l *Field, fp int, init *Nodes, ddd *Node) []*Node {
	esc := uint16(EscUnknown)
	if ddd != nil {
		esc = ddd.Esc
	}

	tslice := typSlice(l.Type.Elem())
	tslice.Noalg = true

	var n *Node
	if len(lr0) == 0 {
		n = nodnil()
		n.Type = tslice
	} else {
		n = Nod(OCOMPLIT, nil, typenod(tslice))
		if ddd != nil && prealloc[ddd] != nil {
			prealloc[n] = prealloc[ddd] // temporary to use
		}
		n.List.Set(lr0)
		n.Esc = esc
		n = typecheck(n, Erv)
		if n.Type == nil {
			Fatalf("mkdotargslice: typecheck failed")
		}
		n = walkexpr(n, init)
	}

	a := Nod(OAS, nodarg(l, fp), n)
	nn = append(nn, convas(a, init))
	return nn
}

// helpers for shape errors
func dumptypes(nl *Type, what string) string {
	s := ""
	for _, l := range nl.Fields().Slice() {
		if s != "" {
			s += ", "
		}
		s += Fldconv(l, 0)
	}
	if s == "" {
		s = fmt.Sprintf("[no arguments %s]", what)
	}
	return s
}

func dumpnodetypes(l []*Node, what string) string {
	s := ""
	for _, r := range l {
		if s != "" {
			s += ", "
		}
		s += Tconv(r.Type, 0)
	}
	if s == "" {
		s = fmt.Sprintf("[no arguments %s]", what)
	}
	return s
}

// check assign expression list to
// a type list. called in
//	return expr-list
//	func(expr-list)
func ascompatte(op Op, call *Node, isddd bool, nl *Type, lr []*Node, fp int, init *Nodes) []*Node {
	lr0 := lr
	l, savel := IterFields(nl)
	var r *Node
	if len(lr) > 0 {
		r = lr[0]
	}
	var nn []*Node

	// f(g()) where g has multiple return values
	if r != nil && len(lr) <= 1 && r.Type.IsFuncArgStruct() {
		// optimization - can do block copy
		if eqtypenoname(r.Type, nl) {
			arg := nodarg(nl, fp)
			r = Nod(OCONVNOP, r, nil)
			r.Type = arg.Type
			nn = []*Node{convas(Nod(OAS, arg, r), init)}
			goto ret
		}

		// conversions involved.
		// copy into temporaries.
		var alist []*Node

		for _, l := range r.Type.Fields().Slice() {
			tmp := temp(l.Type)
			alist = append(alist, tmp)
		}

		a := Nod(OAS2, nil, nil)
		a.List.Set(alist)
		a.Rlist.Set(lr)
		a = typecheck(a, Etop)
		a = walkstmt(a)
		init.Append(a)
		lr = alist
		r = lr[0]
		l, savel = IterFields(nl)
	}

	for {
		if l != nil && l.Isddd {
			// the ddd parameter must be last
			ll := savel.Next()

			if ll != nil {
				Yyerror("... must be last argument")
			}

			// special case --
			// only if we are assigning a single ddd
			// argument to a ddd parameter then it is
			// passed through unencapsulated
			if r != nil && len(lr) <= 1 && isddd && Eqtype(l.Type, r.Type) {
				a := Nod(OAS, nodarg(l, fp), r)
				a = convas(a, init)
				nn = append(nn, a)
				break
			}

			// normal case -- make a slice of all
			// remaining arguments and pass it to
			// the ddd parameter.
			nn = mkdotargslice(lr, nn, l, fp, init, call.Right)

			break
		}

		if l == nil || r == nil {
			if l != nil || r != nil {
				l1 := dumptypes(nl, "expected")
				l2 := dumpnodetypes(lr0, "given")
				if l != nil {
					Yyerror("not enough arguments to %v\n\t%s\n\t%s", Oconv(op, 0), l1, l2)
				} else {
					Yyerror("too many arguments to %v\n\t%s\n\t%s", Oconv(op, 0), l1, l2)
				}
			}

			break
		}

		a := Nod(OAS, nodarg(l, fp), r)
		a = convas(a, init)
		nn = append(nn, a)

		l = savel.Next()
		r = nil
		lr = lr[1:]
		if len(lr) > 0 {
			r = lr[0]
		}
	}

ret:
	for _, n := range nn {
		n.Typecheck = 1
	}
	return nn
}

// generate code for print
func walkprint(nn *Node, init *Nodes) *Node {
	var r *Node
	var n *Node
	var on *Node
	var t *Type
	var et EType

	op := nn.Op
	all := nn.List
	var calls []*Node
	notfirst := false

	// Hoist all the argument evaluation up before the lock.
	walkexprlistcheap(all.Slice(), init)

	calls = append(calls, mkcall("printlock", nil, init))
	for i1, n1 := range all.Slice() {
		if notfirst {
			calls = append(calls, mkcall("printsp", nil, init))
		}

		notfirst = op == OPRINTN

		n = n1
		if n.Op == OLITERAL {
			switch n.Val().Ctype() {
			case CTRUNE:
				n = defaultlit(n, runetype)

			case CTINT:
				n = defaultlit(n, Types[TINT64])

			case CTFLT:
				n = defaultlit(n, Types[TFLOAT64])
			}
		}

		if n.Op != OLITERAL && n.Type != nil && n.Type.Etype == TIDEAL {
			n = defaultlit(n, Types[TINT64])
		}
		n = defaultlit(n, nil)
		all.SetIndex(i1, n)
		if n.Type == nil || n.Type.Etype == TFORW {
			continue
		}

		t = n.Type
		et = n.Type.Etype
		if n.Type.IsInterface() {
			if n.Type.IsEmptyInterface() {
				on = syslook("printeface")
			} else {
				on = syslook("printiface")
			}
			on = substArgTypes(on, n.Type) // any-1
		} else if n.Type.IsPtr() || et == TCHAN || et == TMAP || et == TFUNC || et == TUNSAFEPTR {
			on = syslook("printpointer")
			on = substArgTypes(on, n.Type) // any-1
		} else if n.Type.IsSlice() {
			on = syslook("printslice")
			on = substArgTypes(on, n.Type) // any-1
		} else if Isint[et] {
			if et == TUINT64 {
				if (t.Sym.Pkg == Runtimepkg || compiling_runtime) && t.Sym.Name == "hex" {
					on = syslook("printhex")
				} else {
					on = syslook("printuint")
				}
			} else {
				on = syslook("printint")
			}
		} else if Isfloat[et] {
			on = syslook("printfloat")
		} else if Iscomplex[et] {
			on = syslook("printcomplex")
		} else if et == TBOOL {
			on = syslook("printbool")
		} else if et == TSTRING {
			on = syslook("printstring")
		} else {
			badtype(OPRINT, n.Type, nil)
			continue
		}

		t = on.Type.Params().Field(0).Type

		if !Eqtype(t, n.Type) {
			n = Nod(OCONV, n, nil)
			n.Type = t
		}

		r = Nod(OCALL, on, nil)
		r.List.Append(n)
		calls = append(calls, r)
	}

	if op == OPRINTN {
		calls = append(calls, mkcall("printnl", nil, nil))
	}

	calls = append(calls, mkcall("printunlock", nil, init))

	typecheckslice(calls, Etop)
	walkexprlist(calls, init)

	r = Nod(OEMPTY, nil, nil)
	r = typecheck(r, Etop)
	r = walkexpr(r, init)
	r.Ninit.Set(calls)
	return r
}

func callnew(t *Type) *Node {
	dowidth(t)
	fn := syslook("newobject")
	fn = substArgTypes(fn, t)
	v := mkcall1(fn, Ptrto(t), nil, typename(t))
	v.NonNil = true
	return v
}

func iscallret(n *Node) bool {
	n = outervalue(n)
	return n.Op == OINDREG && n.Reg == int16(Thearch.REGSP)
}

func isstack(n *Node) bool {
	n = outervalue(n)

	// If n is *autotmp and autotmp = &foo, replace n with foo.
	// We introduce such temps when initializing struct literals.
	if n.Op == OIND && n.Left.Op == ONAME && strings.HasPrefix(n.Left.Sym.Name, "autotmp_") {
		defn := n.Left.Name.Defn
		if defn != nil && defn.Op == OAS && defn.Right.Op == OADDR {
			n = defn.Right.Left
		}
	}

	switch n.Op {
	case OINDREG:
		return n.Reg == int16(Thearch.REGSP)

	case ONAME:
		switch n.Class {
		case PAUTO, PPARAM, PPARAMOUT:
			return true
		}
	}

	return false
}

func isglobal(n *Node) bool {
	n = outervalue(n)

	switch n.Op {
	case ONAME:
		switch n.Class {
		case PEXTERN:
			return true
		}
	}

	return false
}

// Do we need a write barrier for the assignment l = r?
func needwritebarrier(l *Node, r *Node) bool {
	if !use_writebarrier {
		return false
	}

	if l == nil || isblank(l) {
		return false
	}

	// No write barrier for write of non-pointers.
	dowidth(l.Type)

	if !haspointers(l.Type) {
		return false
	}

	// No write barrier for write to stack.
	if isstack(l) {
		return false
	}

	// No write barrier for implicit zeroing.
	if r == nil {
		return false
	}

	// Ignore no-op conversions when making decision.
	// Ensures that xp = unsafe.Pointer(&x) is treated
	// the same as xp = &x.
	for r.Op == OCONVNOP {
		r = r.Left
	}

	// No write barrier for zeroing or initialization to constant.
	if iszero(r) || r.Op == OLITERAL {
		return false
	}

	// No write barrier for storing static (read-only) data.
	if r.Op == ONAME && strings.HasPrefix(r.Sym.Name, "statictmp_") {
		return false
	}

	// No write barrier for storing address of stack values,
	// which are guaranteed only to be written to the stack.
	if r.Op == OADDR && isstack(r.Left) {
		return false
	}

	// No write barrier for storing address of global, which
	// is live no matter what.
	if r.Op == OADDR && isglobal(r.Left) {
		return false
	}

	// No write barrier for storing global function, which is live
	// no matter what.
	if r.Op == ONAME && r.Class == PFUNC {
		return false
	}

	// Otherwise, be conservative and use write barrier.
	return true
}

// TODO(rsc): Perhaps componentgen should run before this.

func applywritebarrier(n *Node) *Node {
	if n.Left != nil && n.Right != nil && needwritebarrier(n.Left, n.Right) {
		if Debug_wb > 1 {
			Warnl(n.Lineno, "marking %v for barrier", Nconv(n.Left, 0))
		}
		n.Op = OASWB
		return n
	}
	return n
}

func convas(n *Node, init *Nodes) *Node {
	if n.Op != OAS {
		Fatalf("convas: not OAS %v", Oconv(n.Op, 0))
	}

	n.Typecheck = 1

	var lt *Type
	var rt *Type
	if n.Left == nil || n.Right == nil {
		goto out
	}

	lt = n.Left.Type
	rt = n.Right.Type
	if lt == nil || rt == nil {
		goto out
	}

	if isblank(n.Left) {
		n.Right = defaultlit(n.Right, nil)
		goto out
	}

	if n.Left.Op == OINDEXMAP {
		map_ := n.Left.Left
		key := n.Left.Right
		val := n.Right
		map_ = walkexpr(map_, init)
		key = walkexpr(key, init)
		val = walkexpr(val, init)

		// orderexpr made sure key and val are addressable.
		key = Nod(OADDR, key, nil)

		val = Nod(OADDR, val, nil)
		n = mkcall1(mapfn("mapassign1", map_.Type), nil, init, typename(map_.Type), map_, key, val)
		goto out
	}

	if !Eqtype(lt, rt) {
		n.Right = assignconv(n.Right, lt, "assignment")
		n.Right = walkexpr(n.Right, init)
	}

out:
	ullmancalc(n)
	return n
}

// from ascompat[te]
// evaluating actual function arguments.
//	f(a,b)
// if there is exactly one function expr,
// then it is done first. otherwise must
// make temp variables
func reorder1(all []*Node) []*Node {
	c := 0 // function calls
	t := 0 // total parameters

	for _, n := range all {
		t++
		ullmancalc(n)
		if n.Ullman >= UINF {
			c++
		}
	}

	if c == 0 || t == 1 {
		return all
	}

	var g []*Node // fncalls assigned to tempnames
	var f *Node   // last fncall assigned to stack
	var r []*Node // non fncalls and tempnames assigned to stack
	d := 0
	var a *Node
	for _, n := range all {
		if n.Ullman < UINF {
			r = append(r, n)
			continue
		}

		d++
		if d == c {
			f = n
			continue
		}

		// make assignment of fncall to tempname
		a = temp(n.Right.Type)

		a = Nod(OAS, a, n.Right)
		g = append(g, a)

		// put normal arg assignment on list
		// with fncall replaced by tempname
		n.Right = a.Left

		r = append(r, n)
	}

	if f != nil {
		g = append(g, f)
	}
	return append(g, r...)
}

// from ascompat[ee]
//	a,b = c,d
// simultaneous assignment. there cannot
// be later use of an earlier lvalue.
//
// function calls have been removed.
func reorder3(all []*Node) []*Node {
	var l *Node

	// If a needed expression may be affected by an
	// earlier assignment, make an early copy of that
	// expression and use the copy instead.
	var early []*Node

	var mapinit Nodes
	for i, n := range all {
		l = n.Left

		// Save subexpressions needed on left side.
		// Drill through non-dereferences.
		for {
			if l.Op == ODOT || l.Op == OPAREN {
				l = l.Left
				continue
			}

			if l.Op == OINDEX && l.Left.Type.IsArray() {
				l.Right = reorder3save(l.Right, all, i, &early)
				l = l.Left
				continue
			}

			break
		}

		switch l.Op {
		default:
			Fatalf("reorder3 unexpected lvalue %v", Oconv(l.Op, FmtSharp))

		case ONAME:
			break

		case OINDEX, OINDEXMAP:
			l.Left = reorder3save(l.Left, all, i, &early)
			l.Right = reorder3save(l.Right, all, i, &early)
			if l.Op == OINDEXMAP {
				all[i] = convas(all[i], &mapinit)
			}

		case OIND, ODOTPTR:
			l.Left = reorder3save(l.Left, all, i, &early)
		}

		// Save expression on right side.
		all[i].Right = reorder3save(all[i].Right, all, i, &early)
	}

	early = append(mapinit.Slice(), early...)
	return append(early, all...)
}

// if the evaluation of *np would be affected by the
// assignments in all up to but not including the ith assignment,
// copy into a temporary during *early and
// replace *np with that temp.
// The result of reorder3save MUST be assigned back to n, e.g.
// 	n.Left = reorder3save(n.Left, all, i, early)
func reorder3save(n *Node, all []*Node, i int, early *[]*Node) *Node {
	if !aliased(n, all, i) {
		return n
	}

	q := temp(n.Type)
	q = Nod(OAS, q, n)
	q = typecheck(q, Etop)
	*early = append(*early, q)
	return q.Left
}

// what's the outer value that a write to n affects?
// outer value means containing struct or array.
func outervalue(n *Node) *Node {
	for {
		if n.Op == OXDOT {
			Fatalf("OXDOT in walk")
		}
		if n.Op == ODOT || n.Op == OPAREN || n.Op == OCONVNOP {
			n = n.Left
			continue
		}

		if n.Op == OINDEX && n.Left.Type != nil && n.Left.Type.IsArray() {
			n = n.Left
			continue
		}

		break
	}

	return n
}

// Is it possible that the computation of n might be
// affected by writes in as up to but not including the ith element?
func aliased(n *Node, all []*Node, i int) bool {
	if n == nil {
		return false
	}

	// Treat all fields of a struct as referring to the whole struct.
	// We could do better but we would have to keep track of the fields.
	for n.Op == ODOT {
		n = n.Left
	}

	// Look for obvious aliasing: a variable being assigned
	// during the all list and appearing in n.
	// Also record whether there are any writes to main memory.
	// Also record whether there are any writes to variables
	// whose addresses have been taken.
	memwrite := 0

	varwrite := 0
	var a *Node
	for _, an := range all[:i] {
		a = outervalue(an.Left)

		for a.Op == ODOT {
			a = a.Left
		}

		if a.Op != ONAME {
			memwrite = 1
			continue
		}

		switch n.Class {
		default:
			varwrite = 1
			continue

		case PAUTO, PPARAM, PPARAMOUT:
			if n.Addrtaken {
				varwrite = 1
				continue
			}

			if vmatch2(a, n) {
				// Direct hit.
				return true
			}
		}
	}

	// The variables being written do not appear in n.
	// However, n might refer to computed addresses
	// that are being written.

	// If no computed addresses are affected by the writes, no aliasing.
	if memwrite == 0 && varwrite == 0 {
		return false
	}

	// If n does not refer to computed addresses
	// (that is, if n only refers to variables whose addresses
	// have not been taken), no aliasing.
	if varexpr(n) {
		return false
	}

	// Otherwise, both the writes and n refer to computed memory addresses.
	// Assume that they might conflict.
	return true
}

// does the evaluation of n only refer to variables
// whose addresses have not been taken?
// (and no other memory)
func varexpr(n *Node) bool {
	if n == nil {
		return true
	}

	switch n.Op {
	case OLITERAL:
		return true

	case ONAME:
		switch n.Class {
		case PAUTO, PPARAM, PPARAMOUT:
			if !n.Addrtaken {
				return true
			}
		}

		return false

	case OADD,
		OSUB,
		OOR,
		OXOR,
		OMUL,
		ODIV,
		OMOD,
		OLSH,
		ORSH,
		OAND,
		OANDNOT,
		OPLUS,
		OMINUS,
		OCOM,
		OPAREN,
		OANDAND,
		OOROR,
		OCONV,
		OCONVNOP,
		OCONVIFACE,
		ODOTTYPE:
		return varexpr(n.Left) && varexpr(n.Right)

	case ODOT: // but not ODOTPTR
		// Should have been handled in aliased.
		Fatalf("varexpr unexpected ODOT")
	}

	// Be conservative.
	return false
}

// is the name l mentioned in r?
func vmatch2(l *Node, r *Node) bool {
	if r == nil {
		return false
	}
	switch r.Op {
	// match each right given left
	case ONAME:
		return l == r

	case OLITERAL:
		return false
	}

	if vmatch2(l, r.Left) {
		return true
	}
	if vmatch2(l, r.Right) {
		return true
	}
	for _, n := range r.List.Slice() {
		if vmatch2(l, n) {
			return true
		}
	}
	return false
}

// is any name mentioned in l also mentioned in r?
// called by sinit.go
func vmatch1(l *Node, r *Node) bool {
	// isolate all left sides
	if l == nil || r == nil {
		return false
	}
	switch l.Op {
	case ONAME:
		switch l.Class {
		case PPARAM, PPARAMREF, PAUTO:
			break

			// assignment to non-stack variable
		// must be delayed if right has function calls.
		default:
			if r.Ullman >= UINF {
				return true
			}
		}

		return vmatch2(l, r)

	case OLITERAL:
		return false
	}

	if vmatch1(l.Left, r) {
		return true
	}
	if vmatch1(l.Right, r) {
		return true
	}
	for _, n := range l.List.Slice() {
		if vmatch1(n, r) {
			return true
		}
	}
	return false
}

// paramstoheap returns code to allocate memory for heap-escaped parameters
// and to copy non-result prameters' values from the stack.
// If out is true, then code is also produced to zero-initialize their
// stack memory addresses.
func paramstoheap(params *Type, out bool) []*Node {
	var nn []*Node
	for _, t := range params.Fields().Slice() {
		v := t.Nname
		if v != nil && v.Sym != nil && strings.HasPrefix(v.Sym.Name, "~r") { // unnamed result
			v = nil
		}

		// For precise stacks, the garbage collector assumes results
		// are always live, so zero them always.
		if out {
			// Defer might stop a panic and show the
			// return values as they exist at the time of panic.
			// Make sure to zero them on entry to the function.
			nn = append(nn, Nod(OAS, nodarg(t, -1), nil))
		}

		if v == nil || v.Class&PHEAP == 0 {
			continue
		}

		// generate allocation & copying code
		if compiling_runtime {
			Yyerror("%v escapes to heap, not allowed in runtime.", v)
		}
		if prealloc[v] == nil {
			prealloc[v] = callnew(v.Type)
		}
		nn = append(nn, Nod(OAS, v.Name.Heapaddr, prealloc[v]))
		if v.Class&^PHEAP != PPARAMOUT {
			as := Nod(OAS, v, v.Name.Param.Stackparam)
			v.Name.Param.Stackparam.Typecheck = 1
			as = typecheck(as, Etop)
			as = applywritebarrier(as)
			nn = append(nn, as)
		}
	}

	return nn
}

// returnsfromheap returns code to copy values for heap-escaped parameters
// back to the stack.
func returnsfromheap(params *Type) []*Node {
	var nn []*Node
	for _, t := range params.Fields().Slice() {
		v := t.Nname
		if v == nil || v.Class != PHEAP|PPARAMOUT {
			continue
		}
		nn = append(nn, Nod(OAS, v.Name.Param.Stackparam, v))
	}

	return nn
}

// heapmoves generates code to handle migrating heap-escaped parameters
// between the stack and the heap. The generated code is added to Curfn's
// Enter and Exit lists.
func heapmoves() {
	lno := lineno
	lineno = Curfn.Lineno
	nn := paramstoheap(Curfn.Type.Recvs(), false)
	nn = append(nn, paramstoheap(Curfn.Type.Params(), false)...)
	nn = append(nn, paramstoheap(Curfn.Type.Results(), true)...)
	Curfn.Func.Enter.Append(nn...)
	lineno = Curfn.Func.Endlineno
	Curfn.Func.Exit.Append(returnsfromheap(Curfn.Type.Results())...)
	lineno = lno
}

func vmkcall(fn *Node, t *Type, init *Nodes, va []*Node) *Node {
	if fn.Type == nil || fn.Type.Etype != TFUNC {
		Fatalf("mkcall %v %v", fn, fn.Type)
	}

	n := fn.Type.Params().NumFields()

	r := Nod(OCALL, fn, nil)
	r.List.Set(va[:n])
	if fn.Type.Results().NumFields() > 0 {
		r = typecheck(r, Erv|Efnstruct)
	} else {
		r = typecheck(r, Etop)
	}
	r = walkexpr(r, init)
	r.Type = t
	return r
}

func mkcall(name string, t *Type, init *Nodes, args ...*Node) *Node {
	return vmkcall(syslook(name), t, init, args)
}

func mkcall1(fn *Node, t *Type, init *Nodes, args ...*Node) *Node {
	return vmkcall(fn, t, init, args)
}

func conv(n *Node, t *Type) *Node {
	if Eqtype(n.Type, t) {
		return n
	}
	n = Nod(OCONV, n, nil)
	n.Type = t
	n = typecheck(n, Erv)
	return n
}

func chanfn(name string, n int, t *Type) *Node {
	if !t.IsChan() {
		Fatalf("chanfn %v", t)
	}
	fn := syslook(name)
	switch n {
	default:
		Fatalf("chanfn %d", n)
	case 1:
		fn = substArgTypes(fn, t.Elem())
	case 2:
		fn = substArgTypes(fn, t.Elem(), t.Elem())
	}
	return fn
}

func mapfn(name string, t *Type) *Node {
	if !t.IsMap() {
		Fatalf("mapfn %v", t)
	}
	fn := syslook(name)
	fn = substArgTypes(fn, t.Key(), t.Val(), t.Key(), t.Val())
	return fn
}

func mapfndel(name string, t *Type) *Node {
	if !t.IsMap() {
		Fatalf("mapfn %v", t)
	}
	fn := syslook(name)
	fn = substArgTypes(fn, t.Key(), t.Val(), t.Key())
	return fn
}

func writebarrierfn(name string, l *Type, r *Type) *Node {
	fn := syslook(name)
	fn = substArgTypes(fn, l, r)
	return fn
}

func addstr(n *Node, init *Nodes) *Node {
	// orderexpr rewrote OADDSTR to have a list of strings.
	c := n.List.Len()

	if c < 2 {
		Yyerror("addstr count %d too small", c)
	}

	buf := nodnil()
	if n.Esc == EscNone {
		sz := int64(0)
		for _, n1 := range n.List.Slice() {
			if n1.Op == OLITERAL {
				sz += int64(len(n1.Val().U.(string)))
			}
		}

		// Don't allocate the buffer if the result won't fit.
		if sz < tmpstringbufsize {
			// Create temporary buffer for result string on stack.
			t := aindex(Nodintconst(tmpstringbufsize), Types[TUINT8])

			buf = Nod(OADDR, temp(t), nil)
		}
	}

	// build list of string arguments
	args := []*Node{buf}
	for _, n2 := range n.List.Slice() {
		args = append(args, conv(n2, Types[TSTRING]))
	}

	var fn string
	if c <= 5 {
		// small numbers of strings use direct runtime helpers.
		// note: orderexpr knows this cutoff too.
		fn = fmt.Sprintf("concatstring%d", c)
	} else {
		// large numbers of strings are passed to the runtime as a slice.
		fn = "concatstrings"

		t := typSlice(Types[TSTRING])
		slice := Nod(OCOMPLIT, nil, typenod(t))
		if prealloc[n] != nil {
			prealloc[slice] = prealloc[n]
		}
		slice.List.Set(args[1:]) // skip buf arg
		args = []*Node{buf, slice}
		slice.Esc = EscNone
	}

	cat := syslook(fn)
	r := Nod(OCALL, cat, nil)
	r.List.Set(args)
	r = typecheck(r, Erv)
	r = walkexpr(r, init)
	r.Type = n.Type

	return r
}

// expand append(l1, l2...) to
//   init {
//     s := l1
//     n := len(s) + len(l2)
//     // Compare as uint so growslice can panic on overflow.
//     if uint(n) > uint(cap(s)) {
//       s = growslice(s, n)
//     }
//     s = s[:n]
//     memmove(&s[len(l1)], &l2[0], len(l2)*sizeof(T))
//   }
//   s
//
// l2 is allowed to be a string.
func appendslice(n *Node, init *Nodes) *Node {
	walkexprlistsafe(n.List.Slice(), init)

	// walkexprlistsafe will leave OINDEX (s[n]) alone if both s
	// and n are name or literal, but those may index the slice we're
	// modifying here. Fix explicitly.
	ls := n.List.Slice()
	for i1, n1 := range ls {
		ls[i1] = cheapexpr(n1, init)
	}

	l1 := n.List.First()
	l2 := n.List.Second()

	var l []*Node

	// var s []T
	s := temp(l1.Type)
	l = append(l, Nod(OAS, s, l1)) // s = l1

	// n := len(s) + len(l2)
	nn := temp(Types[TINT])
	l = append(l, Nod(OAS, nn, Nod(OADD, Nod(OLEN, s, nil), Nod(OLEN, l2, nil))))

	// if uint(n) > uint(cap(s))
	nif := Nod(OIF, nil, nil)
	nif.Left = Nod(OGT, Nod(OCONV, nn, nil), Nod(OCONV, Nod(OCAP, s, nil), nil))
	nif.Left.Left.Type = Types[TUINT]
	nif.Left.Right.Type = Types[TUINT]

	// instantiate growslice(Type*, []any, int) []any
	fn := syslook("growslice")
	fn = substArgTypes(fn, s.Type.Elem(), s.Type.Elem())

	// s = growslice(T, s, n)
	nif.Nbody.Set1(Nod(OAS, s, mkcall1(fn, s.Type, &nif.Ninit, typename(s.Type.Elem()), s, nn)))
	l = append(l, nif)

	// s = s[:n]
	nt := Nod(OSLICE, s, Nod(OKEY, nil, nn))
	nt.Etype = 1
	l = append(l, Nod(OAS, s, nt))

	if haspointers(l1.Type.Elem()) {
		// copy(s[len(l1):], l2)
		nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), nil))

		nptr1.Etype = 1
		nptr2 := l2
		fn := syslook("typedslicecopy")
		fn = substArgTypes(fn, l1.Type, l2.Type)
		var ln Nodes
		ln.Set(l)
		nt := mkcall1(fn, Types[TINT], &ln, typename(l1.Type.Elem()), nptr1, nptr2)
		l = append(ln.Slice(), nt)
	} else if instrumenting {
		// rely on runtime to instrument copy.
		// copy(s[len(l1):], l2)
		nptr1 := Nod(OSLICE, s, Nod(OKEY, Nod(OLEN, l1, nil), nil))

		nptr1.Etype = 1
		nptr2 := l2
		var fn *Node
		if l2.Type.IsString() {
			fn = syslook("slicestringcopy")
		} else {
			fn = syslook("slicecopy")
		}
		fn = substArgTypes(fn, l1.Type, l2.Type)
		var ln Nodes
		ln.Set(l)
		nt := mkcall1(fn, Types[TINT], &ln, nptr1, nptr2, Nodintconst(s.Type.Elem().Width))
		l = append(ln.Slice(), nt)
	} else {
		// memmove(&s[len(l1)], &l2[0], len(l2)*sizeof(T))
		nptr1 := Nod(OINDEX, s, Nod(OLEN, l1, nil))
		nptr1.Bounded = true

		nptr1 = Nod(OADDR, nptr1, nil)

		nptr2 := Nod(OSPTR, l2, nil)

		fn := syslook("memmove")
		fn = substArgTypes(fn, s.Type.Elem(), s.Type.Elem())

		var ln Nodes
		ln.Set(l)
		nwid := cheapexpr(conv(Nod(OLEN, l2, nil), Types[TUINTPTR]), &ln)

		nwid = Nod(OMUL, nwid, Nodintconst(s.Type.Elem().Width))
		nt := mkcall1(fn, nil, &ln, nptr1, nptr2, nwid)
		l = append(ln.Slice(), nt)
	}

	typecheckslice(l, Etop)
	walkstmtlist(l)
	init.Append(l...)
	return s
}

// Rewrite append(src, x, y, z) so that any side effects in
// x, y, z (including runtime panics) are evaluated in
// initialization statements before the append.
// For normal code generation, stop there and leave the
// rest to cgen_append.
//
// For race detector, expand append(src, a [, b]* ) to
//
//   init {
//     s := src
//     const argc = len(args) - 1
//     if cap(s) - len(s) < argc {
//	    s = growslice(s, len(s)+argc)
//     }
//     n := len(s)
//     s = s[:n+argc]
//     s[n] = a
//     s[n+1] = b
//     ...
//   }
//   s
func walkappend(n *Node, init *Nodes, dst *Node) *Node {
	if !samesafeexpr(dst, n.List.First()) {
		n.List.SetIndex(0, safeexpr(n.List.Index(0), init))
		n.List.SetIndex(0, walkexpr(n.List.Index(0), init))
	}
	walkexprlistsafe(n.List.Slice()[1:], init)

	// walkexprlistsafe will leave OINDEX (s[n]) alone if both s
	// and n are name or literal, but those may index the slice we're
	// modifying here. Fix explicitly.
	// Using cheapexpr also makes sure that the evaluation
	// of all arguments (and especially any panics) happen
	// before we begin to modify the slice in a visible way.
	ls := n.List.Slice()[1:]
	for i, n := range ls {
		ls[i] = cheapexpr(n, init)
	}

	nsrc := n.List.First()

	argc := n.List.Len() - 1
	if argc < 1 {
		return nsrc
	}

	// General case, with no function calls left as arguments.
	// Leave for gen, except that instrumentation requires old form.
	if !instrumenting {
		return n
	}

	var l []*Node

	ns := temp(nsrc.Type)
	l = append(l, Nod(OAS, ns, nsrc)) // s = src

	na := Nodintconst(int64(argc)) // const argc
	nx := Nod(OIF, nil, nil)       // if cap(s) - len(s) < argc
	nx.Left = Nod(OLT, Nod(OSUB, Nod(OCAP, ns, nil), Nod(OLEN, ns, nil)), na)

	fn := syslook("growslice") //   growslice(<type>, old []T, mincap int) (ret []T)
	fn = substArgTypes(fn, ns.Type.Elem(), ns.Type.Elem())

	nx.Nbody.Set1(Nod(OAS, ns,
		mkcall1(fn, ns.Type, &nx.Ninit, typename(ns.Type.Elem()), ns,
			Nod(OADD, Nod(OLEN, ns, nil), na))))

	l = append(l, nx)

	nn := temp(Types[TINT])
	l = append(l, Nod(OAS, nn, Nod(OLEN, ns, nil))) // n = len(s)

	nx = Nod(OSLICE, ns, Nod(OKEY, nil, Nod(OADD, nn, na))) // ...s[:n+argc]
	nx.Etype = 1
	l = append(l, Nod(OAS, ns, nx)) // s = s[:n+argc]

	ls = n.List.Slice()[1:]
	for i, n := range ls {
		nx = Nod(OINDEX, ns, nn) // s[n] ...
		nx.Bounded = true
		l = append(l, Nod(OAS, nx, n)) // s[n] = arg
		if i+1 < len(ls) {
			l = append(l, Nod(OAS, nn, Nod(OADD, nn, Nodintconst(1)))) // n = n + 1
		}
	}

	typecheckslice(l, Etop)
	walkstmtlist(l)
	init.Append(l...)
	return ns
}

// Lower copy(a, b) to a memmove call or a runtime call.
//
// init {
//   n := len(a)
//   if n > len(b) { n = len(b) }
//   memmove(a.ptr, b.ptr, n*sizeof(elem(a)))
// }
// n;
//
// Also works if b is a string.
//
func copyany(n *Node, init *Nodes, runtimecall bool) *Node {
	if haspointers(n.Left.Type.Elem()) {
		fn := writebarrierfn("typedslicecopy", n.Left.Type, n.Right.Type)
		return mkcall1(fn, n.Type, init, typename(n.Left.Type.Elem()), n.Left, n.Right)
	}

	if runtimecall {
		var fn *Node
		if n.Right.Type.IsString() {
			fn = syslook("slicestringcopy")
		} else {
			fn = syslook("slicecopy")
		}
		fn = substArgTypes(fn, n.Left.Type, n.Right.Type)
		return mkcall1(fn, n.Type, init, n.Left, n.Right, Nodintconst(n.Left.Type.Elem().Width))
	}

	n.Left = walkexpr(n.Left, init)
	n.Right = walkexpr(n.Right, init)
	nl := temp(n.Left.Type)
	nr := temp(n.Right.Type)
	var l []*Node
	l = append(l, Nod(OAS, nl, n.Left))
	l = append(l, Nod(OAS, nr, n.Right))

	nfrm := Nod(OSPTR, nr, nil)
	nto := Nod(OSPTR, nl, nil)

	nlen := temp(Types[TINT])

	// n = len(to)
	l = append(l, Nod(OAS, nlen, Nod(OLEN, nl, nil)))

	// if n > len(frm) { n = len(frm) }
	nif := Nod(OIF, nil, nil)

	nif.Left = Nod(OGT, nlen, Nod(OLEN, nr, nil))
	nif.Nbody.Append(Nod(OAS, nlen, Nod(OLEN, nr, nil)))
	l = append(l, nif)

	// Call memmove.
	fn := syslook("memmove")

	fn = substArgTypes(fn, nl.Type.Elem(), nl.Type.Elem())
	nwid := temp(Types[TUINTPTR])
	l = append(l, Nod(OAS, nwid, conv(nlen, Types[TUINTPTR])))
	nwid = Nod(OMUL, nwid, Nodintconst(nl.Type.Elem().Width))
	l = append(l, mkcall1(fn, nil, init, nto, nfrm, nwid))

	typecheckslice(l, Etop)
	walkstmtlist(l)
	init.Append(l...)
	return nlen
}

func eqfor(t *Type, needsize *int) *Node {
	// Should only arrive here with large memory or
	// a struct/array containing a non-memory field/element.
	// Small memory is handled inline, and single non-memory
	// is handled during type check (OCMPSTR etc).
	switch a, _ := algtype1(t); a {
	case AMEM:
		n := syslook("memequal")
		n = substArgTypes(n, t, t)
		*needsize = 1
		return n
	case ASPECIAL:
		sym := typesymprefix(".eq", t)
		n := newname(sym)
		n.Class = PFUNC
		ntype := Nod(OTFUNC, nil, nil)
		ntype.List.Append(Nod(ODCLFIELD, nil, typenod(Ptrto(t))))
		ntype.List.Append(Nod(ODCLFIELD, nil, typenod(Ptrto(t))))
		ntype.Rlist.Append(Nod(ODCLFIELD, nil, typenod(Types[TBOOL])))
		ntype = typecheck(ntype, Etype)
		n.Type = ntype.Type
		*needsize = 0
		return n
	}
	Fatalf("eqfor %v", t)
	return nil
}

// The result of walkcompare MUST be assigned back to n, e.g.
// 	n.Left = walkcompare(n.Left, init)
func walkcompare(n *Node, init *Nodes) *Node {
	// Given interface value l and concrete value r, rewrite
	//   l == r
	// to
	//   x, ok := l.(type(r)); ok && x == r
	// Handle != similarly.
	// This avoids the allocation that would be required
	// to convert r to l for comparison.
	var l *Node

	var r *Node
	if n.Left.Type.IsInterface() && !n.Right.Type.IsInterface() {
		l = n.Left
		r = n.Right
	} else if !n.Left.Type.IsInterface() && n.Right.Type.IsInterface() {
		l = n.Right
		r = n.Left
	}

	if l != nil {
		x := temp(r.Type)
		if haspointers(r.Type) {
			a := Nod(OAS, x, nil)
			a = typecheck(a, Etop)
			init.Append(a)
		}
		ok := temp(Types[TBOOL])

		// l.(type(r))
		a := Nod(ODOTTYPE, l, nil)

		a.Type = r.Type

		// x, ok := l.(type(r))
		expr := Nod(OAS2, nil, nil)

		expr.List.Append(x)
		expr.List.Append(ok)
		expr.Rlist.Append(a)
		expr = typecheck(expr, Etop)
		expr = walkexpr(expr, init)

		if n.Op == OEQ {
			r = Nod(OANDAND, ok, Nod(OEQ, x, r))
		} else {
			r = Nod(OOROR, Nod(ONOT, ok, nil), Nod(ONE, x, r))
		}
		init.Append(expr)
		n = finishcompare(n, r, init)
		return n
	}

	// Must be comparison of array or struct.
	// Otherwise back end handles it.
	t := n.Left.Type

	switch t.Etype {
	default:
		return n

	case TARRAY, TSTRUCT:
		break
	}

	cmpl := n.Left
	for cmpl != nil && cmpl.Op == OCONVNOP {
		cmpl = cmpl.Left
	}
	cmpr := n.Right
	for cmpr != nil && cmpr.Op == OCONVNOP {
		cmpr = cmpr.Left
	}

	if !islvalue(cmpl) || !islvalue(cmpr) {
		Fatalf("arguments of comparison must be lvalues - %v %v", cmpl, cmpr)
	}

	l = temp(Ptrto(t))
	a := Nod(OAS, l, Nod(OADDR, cmpl, nil))
	a.Right.Etype = 1 // addr does not escape
	a = typecheck(a, Etop)
	init.Append(a)

	r = temp(Ptrto(t))
	a = Nod(OAS, r, Nod(OADDR, cmpr, nil))
	a.Right.Etype = 1 // addr does not escape
	a = typecheck(a, Etop)
	init.Append(a)

	var andor Op = OANDAND
	if n.Op == ONE {
		andor = OOROR
	}

	var expr *Node
	if t.Etype == TARRAY && t.NumElem() <= 4 && issimple[t.Elem().Etype] {
		// Four or fewer elements of a basic type.
		// Unroll comparisons.
		var li *Node
		var ri *Node
		for i := 0; int64(i) < t.NumElem(); i++ {
			li = Nod(OINDEX, l, Nodintconst(int64(i)))
			ri = Nod(OINDEX, r, Nodintconst(int64(i)))
			a = Nod(n.Op, li, ri)
			if expr == nil {
				expr = a
			} else {
				expr = Nod(andor, expr, a)
			}
		}

		if expr == nil {
			expr = Nodbool(n.Op == OEQ)
		}
		n = finishcompare(n, expr, init)
		return n
	}

	if t.Etype == TARRAY {
		// Zero- or single-element array, of any type.
		switch t.NumElem() {
		case 0:
			n = finishcompare(n, Nodbool(n.Op == OEQ), init)
			return n
		case 1:
			l0 := Nod(OINDEX, l, Nodintconst(0))
			r0 := Nod(OINDEX, r, Nodintconst(0))
			a := Nod(n.Op, l0, r0)
			n = finishcompare(n, a, init)
			return n
		}
	}

	if t.IsStruct() && t.NumFields() <= 4 {
		// Struct of four or fewer fields.
		// Inline comparisons.
		var li *Node
		var ri *Node
		for _, t1 := range t.Fields().Slice() {
			if isblanksym(t1.Sym) {
				continue
			}
			li = NodSym(OXDOT, l, t1.Sym)
			ri = NodSym(OXDOT, r, t1.Sym)
			a = Nod(n.Op, li, ri)
			if expr == nil {
				expr = a
			} else {
				expr = Nod(andor, expr, a)
			}
		}

		if expr == nil {
			expr = Nodbool(n.Op == OEQ)
		}
		n = finishcompare(n, expr, init)
		return n
	}

	// Chose not to inline. Call equality function directly.
	var needsize int
	call := Nod(OCALL, eqfor(t, &needsize), nil)

	call.List.Append(l)
	call.List.Append(r)
	if needsize != 0 {
		call.List.Append(Nodintconst(t.Width))
	}
	r = call
	if n.Op != OEQ {
		r = Nod(ONOT, r, nil)
	}

	n = finishcompare(n, r, init)
	return n
}

// The result of finishcompare MUST be assigned back to n, e.g.
// 	n.Left = finishcompare(n.Left, x, r, init)
func finishcompare(n, r *Node, init *Nodes) *Node {
	// Use nn here to avoid passing r to typecheck.
	nn := r
	nn = typecheck(nn, Erv)
	nn = walkexpr(nn, init)
	r = nn
	if r.Type != n.Type {
		r = Nod(OCONVNOP, r, nil)
		r.Type = n.Type
		r.Typecheck = 1
		nn = r
	}
	return nn
}

func samecheap(a *Node, b *Node) bool {
	var ar *Node
	var br *Node
	for a != nil && b != nil && a.Op == b.Op {
		switch a.Op {
		default:
			return false

		case ONAME:
			return a == b

		case ODOT, ODOTPTR:
			if a.Sym != b.Sym {
				return false
			}

		case OINDEX:
			ar = a.Right
			br = b.Right
			if !Isconst(ar, CTINT) || !Isconst(br, CTINT) || ar.Val().U.(*Mpint).Cmp(br.Val().U.(*Mpint)) != 0 {
				return false
			}
		}

		a = a.Left
		b = b.Left
	}

	return false
}

// The result of walkrotate MUST be assigned back to n, e.g.
// 	n.Left = walkrotate(n.Left)
func walkrotate(n *Node) *Node {
	if Thearch.LinkArch.InFamily(sys.MIPS64, sys.ARM64, sys.PPC64) {
		return n
	}

	// Want << | >> or >> | << or << ^ >> or >> ^ << on unsigned value.
	l := n.Left

	r := n.Right
	if (n.Op != OOR && n.Op != OXOR) || (l.Op != OLSH && l.Op != ORSH) || (r.Op != OLSH && r.Op != ORSH) || n.Type == nil || n.Type.IsSigned() || l.Op == r.Op {
		return n
	}

	// Want same, side effect-free expression on lhs of both shifts.
	if !samecheap(l.Left, r.Left) {
		return n
	}

	// Constants adding to width?
	w := int(l.Type.Width * 8)

	if Thearch.LinkArch.Family == sys.S390X && w != 32 && w != 64 {
		// only supports 32-bit and 64-bit rotates
		return n
	}

	if Smallintconst(l.Right) && Smallintconst(r.Right) {
		sl := int(l.Right.Int64())
		if sl >= 0 {
			sr := int(r.Right.Int64())
			if sr >= 0 && sl+sr == w {
				// Rewrite left shift half to left rotate.
				if l.Op == OLSH {
					n = l
				} else {
					n = r
				}
				n.Op = OLROT

				// Remove rotate 0 and rotate w.
				s := int(n.Right.Int64())

				if s == 0 || s == w {
					n = n.Left
				}
				return n
			}
		}
		return n
	}

	// TODO: Could allow s and 32-s if s is bounded (maybe s&31 and 32-s&31).
	return n
}

// walkmul rewrites integer multiplication by powers of two as shifts.
// The result of walkmul MUST be assigned back to n, e.g.
// 	n.Left = walkmul(n.Left, init)
func walkmul(n *Node, init *Nodes) *Node {
	if !n.Type.IsInteger() {
		return n
	}

	var nr *Node
	var nl *Node
	if n.Right.Op == OLITERAL {
		nl = n.Left
		nr = n.Right
	} else if n.Left.Op == OLITERAL {
		nl = n.Right
		nr = n.Left
	} else {
		return n
	}

	neg := 0

	// x*0 is 0 (and side effects of x).
	var pow int
	var w int
	if nr.Int64() == 0 {
		cheapexpr(nl, init)
		Nodconst(n, n.Type, 0)
		goto ret
	}

	// nr is a constant.
	pow = powtwo(nr)

	if pow < 0 {
		return n
	}
	if pow >= 1000 {
		// negative power of 2, like -16
		neg = 1

		pow -= 1000
	}

	w = int(nl.Type.Width * 8)
	if pow+1 >= w { // too big, shouldn't happen
		return n
	}

	nl = cheapexpr(nl, init)

	if pow == 0 {
		// x*1 is x
		n = nl

		goto ret
	}

	n = Nod(OLSH, nl, Nodintconst(int64(pow)))

ret:
	if neg != 0 {
		n = Nod(OMINUS, n, nil)
	}

	n = typecheck(n, Erv)
	n = walkexpr(n, init)
	return n
}

// walkdiv rewrites division by a constant as less expensive
// operations.
// The result of walkdiv MUST be assigned back to n, e.g.
// 	n.Left = walkdiv(n.Left, init)
func walkdiv(n *Node, init *Nodes) *Node {
	// if >= 0, nr is 1<<pow // 1 if nr is negative.

	// TODO(minux)
	if Thearch.LinkArch.InFamily(sys.MIPS64, sys.ARM64, sys.PPC64) {
		return n
	}

	if n.Right.Op != OLITERAL {
		return n
	}

	// nr is a constant.
	nl := cheapexpr(n.Left, init)

	nr := n.Right

	// special cases of mod/div
	// by a constant
	w := int(nl.Type.Width * 8)

	s := 0            // 1 if nr is negative.
	pow := powtwo(nr) // if >= 0, nr is 1<<pow
	if pow >= 1000 {
		// negative power of 2
		s = 1

		pow -= 1000
	}

	if pow+1 >= w {
		// divisor too large.
		return n
	}

	if pow < 0 {
		// try to do division by multiply by (2^w)/d
		// see hacker's delight chapter 10
		// TODO: support 64-bit magic multiply here.
		var m Magic
		m.W = w

		if nl.Type.IsSigned() {
			m.Sd = nr.Int64()
			Smagic(&m)
		} else {
			m.Ud = uint64(nr.Int64())
			Umagic(&m)
		}

		if m.Bad != 0 {
			return n
		}

		// We have a quick division method so use it
		// for modulo too.
		if n.Op == OMOD {
			// rewrite as A%B = A - (A/B*B).
			n1 := Nod(ODIV, nl, nr)

			n2 := Nod(OMUL, n1, nr)
			n = Nod(OSUB, nl, n2)
			goto ret
		}

		switch Simtype[nl.Type.Etype] {
		default:
			return n

			// n1 = nl * magic >> w (HMUL)
		case TUINT8, TUINT16, TUINT32:
			var nc Node

			Nodconst(&nc, nl.Type, int64(m.Um))
			n1 := Nod(OHMUL, nl, &nc)
			n1 = typecheck(n1, Erv)
			if m.Ua != 0 {
				// Select a Go type with (at least) twice the width.
				var twide *Type
				switch Simtype[nl.Type.Etype] {
				default:
					return n

				case TUINT8, TUINT16:
					twide = Types[TUINT32]

				case TUINT32:
					twide = Types[TUINT64]

				case TINT8, TINT16:
					twide = Types[TINT32]

				case TINT32:
					twide = Types[TINT64]
				}

				// add numerator (might overflow).
				// n2 = (n1 + nl)
				n2 := Nod(OADD, conv(n1, twide), conv(nl, twide))

				// shift by m.s
				var nc Node

				Nodconst(&nc, Types[TUINT], int64(m.S))
				n = conv(Nod(ORSH, n2, &nc), nl.Type)
			} else {
				// n = n1 >> m.s
				var nc Node

				Nodconst(&nc, Types[TUINT], int64(m.S))
				n = Nod(ORSH, n1, &nc)
			}

			// n1 = nl * magic >> w
		case TINT8, TINT16, TINT32:
			var nc Node

			Nodconst(&nc, nl.Type, m.Sm)
			n1 := Nod(OHMUL, nl, &nc)
			n1 = typecheck(n1, Erv)
			if m.Sm < 0 {
				// add the numerator.
				n1 = Nod(OADD, n1, nl)
			}

			// shift by m.s
			var ns Node

			Nodconst(&ns, Types[TUINT], int64(m.S))
			n2 := conv(Nod(ORSH, n1, &ns), nl.Type)

			// add 1 iff n1 is negative.
			var nneg Node

			Nodconst(&nneg, Types[TUINT], int64(w)-1)
			n3 := Nod(ORSH, nl, &nneg) // n4 = -1 iff n1 is negative.
			n = Nod(OSUB, n2, n3)

			// apply sign.
			if m.Sd < 0 {
				n = Nod(OMINUS, n, nil)
			}
		}

		goto ret
	}

	switch pow {
	case 0:
		if n.Op == OMOD {
			// nl % 1 is zero.
			Nodconst(n, n.Type, 0)
		} else if s != 0 {
			// divide by -1
			n.Op = OMINUS

			n.Right = nil
		} else {
			// divide by 1
			n = nl
		}

	default:
		if n.Type.IsSigned() {
			if n.Op == OMOD {
				// signed modulo 2^pow is like ANDing
				// with the last pow bits, but if nl < 0,
				// nl & (2^pow-1) is (nl+1)%2^pow - 1.
				var nc Node

				Nodconst(&nc, Types[Simtype[TUINT]], int64(w)-1)
				n1 := Nod(ORSH, nl, &nc) // n1 = -1 iff nl < 0.
				if pow == 1 {
					n1 = typecheck(n1, Erv)
					n1 = cheapexpr(n1, init)

					// n = (nl+ε)&1 -ε where ε=1 iff nl<0.
					n2 := Nod(OSUB, nl, n1)

					var nc Node
					Nodconst(&nc, nl.Type, 1)
					n3 := Nod(OAND, n2, &nc)
					n = Nod(OADD, n3, n1)
				} else {
					// n = (nl+ε)&(nr-1) - ε where ε=2^pow-1 iff nl<0.
					var nc Node

					Nodconst(&nc, nl.Type, (1<<uint(pow))-1)
					n2 := Nod(OAND, n1, &nc) // n2 = 2^pow-1 iff nl<0.
					n2 = typecheck(n2, Erv)
					n2 = cheapexpr(n2, init)

					n3 := Nod(OADD, nl, n2)
					n4 := Nod(OAND, n3, &nc)
					n = Nod(OSUB, n4, n2)
				}

				break
			} else {
				// arithmetic right shift does not give the correct rounding.
				// if nl >= 0, nl >> n == nl / nr
				// if nl < 0, we want to add 2^n-1 first.
				var nc Node

				Nodconst(&nc, Types[Simtype[TUINT]], int64(w)-1)
				n1 := Nod(ORSH, nl, &nc) // n1 = -1 iff nl < 0.
				if pow == 1 {
					// nl+1 is nl-(-1)
					n.Left = Nod(OSUB, nl, n1)
				} else {
					// Do a logical right right on -1 to keep pow bits.
					var nc Node

					Nodconst(&nc, Types[Simtype[TUINT]], int64(w)-int64(pow))
					n2 := Nod(ORSH, conv(n1, tounsigned(nl.Type)), &nc)
					n.Left = Nod(OADD, nl, conv(n2, nl.Type))
				}

				// n = (nl + 2^pow-1) >> pow
				n.Op = ORSH

				var n2 Node
				Nodconst(&n2, Types[Simtype[TUINT]], int64(pow))
				n.Right = &n2
				n.Typecheck = 0
			}

			if s != 0 {
				n = Nod(OMINUS, n, nil)
			}
			break
		}

		var nc Node
		if n.Op == OMOD {
			// n = nl & (nr-1)
			n.Op = OAND

			Nodconst(&nc, nl.Type, nr.Int64()-1)
		} else {
			// n = nl >> pow
			n.Op = ORSH

			Nodconst(&nc, Types[Simtype[TUINT]], int64(pow))
		}

		n.Typecheck = 0
		n.Right = &nc
	}

	goto ret

ret:
	n = typecheck(n, Erv)
	n = walkexpr(n, init)
	return n
}

// return 1 if integer n must be in range [0, max), 0 otherwise
func bounded(n *Node, max int64) bool {
	if n.Type == nil || !n.Type.IsInteger() {
		return false
	}

	sign := n.Type.IsSigned()
	bits := int32(8 * n.Type.Width)

	if Smallintconst(n) {
		v := n.Int64()
		return 0 <= v && v < max
	}

	switch n.Op {
	case OAND:
		v := int64(-1)
		if Smallintconst(n.Left) {
			v = n.Left.Int64()
		} else if Smallintconst(n.Right) {
			v = n.Right.Int64()
		}

		if 0 <= v && v < max {
			return true
		}

	case OMOD:
		if !sign && Smallintconst(n.Right) {
			v := n.Right.Int64()
			if 0 <= v && v <= max {
				return true
			}
		}

	case ODIV:
		if !sign && Smallintconst(n.Right) {
			v := n.Right.Int64()
			for bits > 0 && v >= 2 {
				bits--
				v >>= 1
			}
		}

	case ORSH:
		if !sign && Smallintconst(n.Right) {
			v := n.Right.Int64()
			if v > int64(bits) {
				return true
			}
			bits -= int32(v)
		}
	}

	if !sign && bits <= 62 && 1<<uint(bits) <= max {
		return true
	}

	return false
}

// usemethod check interface method calls for uses of reflect.Type.Method.
func usemethod(n *Node) {
	t := n.Left.Type

	// Looking for either of:
	//	Method(int) reflect.Method
	//	MethodByName(string) (reflect.Method, bool)
	//
	// TODO(crawshaw): improve precision of match by working out
	//                 how to check the method name.
	if n := t.Params().NumFields(); n != 1 {
		return
	}
	if n := t.Results().NumFields(); n != 1 && n != 2 {
		return
	}
	p0 := t.Params().Field(0)
	res0 := t.Results().Field(0)
	var res1 *Field
	if t.Results().NumFields() == 2 {
		res1 = t.Results().Field(1)
	}

	if res1 == nil {
		if p0.Type.Etype != TINT {
			return
		}
	} else {
		if !p0.Type.IsString() {
			return
		}
		if !res1.Type.IsBoolean() {
			return
		}
	}
	if Tconv(res0.Type, 0) != "reflect.Method" {
		return
	}

	Curfn.Func.ReflectMethod = true
}

func usefield(n *Node) {
	if obj.Fieldtrack_enabled == 0 {
		return
	}

	switch n.Op {
	default:
		Fatalf("usefield %v", Oconv(n.Op, 0))

	case ODOT, ODOTPTR:
		break
	}
	if n.Sym == nil {
		// No field name.  This DOTPTR was built by the compiler for access
		// to runtime data structures.  Ignore.
		return
	}

	t := n.Left.Type
	if t.IsPtr() {
		t = t.Elem()
	}
	field := dotField[typeSym{t.Orig, n.Sym}]
	if field == nil {
		Fatalf("usefield %v %v without paramfld", n.Left.Type, n.Sym)
	}
	if field.Note == nil || !strings.Contains(*field.Note, "go:\"track\"") {
		return
	}

	outer := n.Left.Type
	if outer.IsPtr() {
		outer = outer.Elem()
	}
	if outer.Sym == nil {
		Yyerror("tracked field must be in named struct type")
	}
	if !exportname(field.Sym.Name) {
		Yyerror("tracked field must be exported (upper case)")
	}

	sym := tracksym(outer, field)
	if Curfn.Func.FieldTrack == nil {
		Curfn.Func.FieldTrack = make(map[*Sym]struct{})
	}
	Curfn.Func.FieldTrack[sym] = struct{}{}
}

func candiscardlist(l Nodes) bool {
	for _, n := range l.Slice() {
		if !candiscard(n) {
			return false
		}
	}
	return true
}

func candiscard(n *Node) bool {
	if n == nil {
		return true
	}

	switch n.Op {
	default:
		return false

		// Discardable as long as the subpieces are.
	case ONAME,
		ONONAME,
		OTYPE,
		OPACK,
		OLITERAL,
		OADD,
		OSUB,
		OOR,
		OXOR,
		OADDSTR,
		OADDR,
		OANDAND,
		OARRAYBYTESTR,
		OARRAYRUNESTR,
		OSTRARRAYBYTE,
		OSTRARRAYRUNE,
		OCAP,
		OCMPIFACE,
		OCMPSTR,
		OCOMPLIT,
		OMAPLIT,
		OSTRUCTLIT,
		OARRAYLIT,
		OPTRLIT,
		OCONV,
		OCONVIFACE,
		OCONVNOP,
		ODOT,
		OEQ,
		ONE,
		OLT,
		OLE,
		OGT,
		OGE,
		OKEY,
		OLEN,
		OMUL,
		OLSH,
		ORSH,
		OAND,
		OANDNOT,
		ONEW,
		ONOT,
		OCOM,
		OPLUS,
		OMINUS,
		OOROR,
		OPAREN,
		ORUNESTR,
		OREAL,
		OIMAG,
		OCOMPLEX:
		break

		// Discardable as long as we know it's not division by zero.
	case ODIV, OMOD:
		if Isconst(n.Right, CTINT) && n.Right.Val().U.(*Mpint).CmpInt64(0) != 0 {
			break
		}
		if Isconst(n.Right, CTFLT) && n.Right.Val().U.(*Mpflt).CmpFloat64(0) != 0 {
			break
		}
		return false

		// Discardable as long as we know it won't fail because of a bad size.
	case OMAKECHAN, OMAKEMAP:
		if Isconst(n.Left, CTINT) && n.Left.Val().U.(*Mpint).CmpInt64(0) == 0 {
			break
		}
		return false

		// Difficult to tell what sizes are okay.
	case OMAKESLICE:
		return false
	}

	if !candiscard(n.Left) || !candiscard(n.Right) || !candiscardlist(n.Ninit) || !candiscardlist(n.Nbody) || !candiscardlist(n.List) || !candiscardlist(n.Rlist) {
		return false
	}

	return true
}

// rewrite
//	print(x, y, z)
// into
//	func(a1, a2, a3) {
//		print(a1, a2, a3)
//	}(x, y, z)
// and same for println.

var walkprintfunc_prgen int

// The result of walkprintfunc MUST be assigned back to n, e.g.
// 	n.Left = walkprintfunc(n.Left, init)
func walkprintfunc(n *Node, init *Nodes) *Node {
	if n.Ninit.Len() != 0 {
		walkstmtlist(n.Ninit.Slice())
		init.AppendNodes(&n.Ninit)
	}

	t := Nod(OTFUNC, nil, nil)
	num := 0
	var printargs []*Node
	var a *Node
	var buf string
	for _, n1 := range n.List.Slice() {
		buf = fmt.Sprintf("a%d", num)
		num++
		a = Nod(ODCLFIELD, newname(Lookup(buf)), typenod(n1.Type))
		t.List.Append(a)
		printargs = append(printargs, a.Left)
	}

	fn := Nod(ODCLFUNC, nil, nil)
	walkprintfunc_prgen++
	buf = fmt.Sprintf("print·%d", walkprintfunc_prgen)
	fn.Func.Nname = newname(Lookup(buf))
	fn.Func.Nname.Name.Defn = fn
	fn.Func.Nname.Name.Param.Ntype = t
	declare(fn.Func.Nname, PFUNC)

	oldfn := Curfn
	Curfn = nil
	funchdr(fn)

	a = Nod(n.Op, nil, nil)
	a.List.Set(printargs)
	a = typecheck(a, Etop)
	a = walkstmt(a)

	fn.Nbody.Set1(a)

	funcbody(fn)

	fn = typecheck(fn, Etop)
	typecheckslice(fn.Nbody.Slice(), Etop)
	xtop = append(xtop, fn)
	Curfn = oldfn

	a = Nod(OCALL, nil, nil)
	a.Left = fn.Func.Nname
	a.List.Set(n.List.Slice())
	a = typecheck(a, Etop)
	a = walkexpr(a, init)
	return a
}