src/cmd/internal/gc/cgen.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"
	"fmt"
)

/*
 * generate:
 *	res = n;
 * simplifies and calls Thearch.Gmove.
 * if wb is true, need to emit write barriers.
 */
func Cgen(n, res *Node) {
	cgen_wb(n, res, false)
}

func cgen_wb(n, res *Node, wb bool) {
	if Debug['g'] != 0 {
		op := "cgen"
		if wb {
			op = "cgen_wb"
		}
		Dump("\n"+op+"-n", n)
		Dump(op+"-res", res)
	}

	if n == nil || n.Type == nil {
		return
	}

	if res == nil || res.Type == nil {
		Fatal("cgen: res nil")
	}

	for n.Op == OCONVNOP {
		n = n.Left
	}

	switch n.Op {
	case OSLICE, OSLICEARR, OSLICESTR, OSLICE3, OSLICE3ARR:
		cgen_slice(n, res, wb)
		return

	case OEFACE:
		if res.Op != ONAME || !res.Addable || wb {
			var n1 Node
			Tempname(&n1, n.Type)
			Cgen_eface(n, &n1)
			cgen_wb(&n1, res, wb)
		} else {
			Cgen_eface(n, res)
		}
		return

	case ODOTTYPE:
		cgen_dottype(n, res, nil, wb)
		return

	case OAPPEND:
		cgen_append(n, res)
		return
	}

	if n.Ullman >= UINF {
		if n.Op == OINDREG {
			Fatal("cgen: this is going to miscompile")
		}
		if res.Ullman >= UINF {
			var n1 Node
			Tempname(&n1, n.Type)
			Cgen(n, &n1)
			cgen_wb(&n1, res, wb)
			return
		}
	}

	if Isfat(n.Type) {
		if n.Type.Width < 0 {
			Fatal("forgot to compute width for %v", n.Type)
		}
		sgen_wb(n, res, n.Type.Width, wb)
		return
	}

	if !res.Addable {
		if n.Ullman > res.Ullman {
			if Ctxt.Arch.Regsize == 4 && Is64(n.Type) {
				var n1 Node
				Tempname(&n1, n.Type)
				Cgen(n, &n1)
				cgen_wb(&n1, res, wb)
				return
			}

			var n1 Node
			Regalloc(&n1, n.Type, res)
			Cgen(n, &n1)
			if n1.Ullman > res.Ullman {
				Dump("n1", &n1)
				Dump("res", res)
				Fatal("loop in cgen")
			}

			cgen_wb(&n1, res, wb)
			Regfree(&n1)
			return
		}

		var f int
		if res.Ullman < UINF {
			if Complexop(n, res) {
				Complexgen(n, res)
				return
			}

			f = 1 // gen thru register
			switch n.Op {
			case OLITERAL:
				if Smallintconst(n) {
					f = 0
				}

			case OREGISTER:
				f = 0
			}

			if !Iscomplex[n.Type.Etype] && Ctxt.Arch.Regsize == 8 && !wb {
				a := Thearch.Optoas(OAS, res.Type)
				var addr obj.Addr
				if Thearch.Sudoaddable(a, res, &addr) {
					var p1 *obj.Prog
					if f != 0 {
						var n2 Node
						Regalloc(&n2, res.Type, nil)
						Cgen(n, &n2)
						p1 = Thearch.Gins(a, &n2, nil)
						Regfree(&n2)
					} else {
						p1 = Thearch.Gins(a, n, nil)
					}
					p1.To = addr
					if Debug['g'] != 0 {
						fmt.Printf("%v [ignore previous line]\n", p1)
					}
					Thearch.Sudoclean()
					return
				}
			}
		}

		if Ctxt.Arch.Thechar == '8' {
			// no registers to speak of
			var n1, n2 Node
			Tempname(&n1, n.Type)
			Cgen(n, &n1)
			Igen(res, &n2, nil)
			cgen_wb(&n1, &n2, wb)
			Regfree(&n2)
			return
		}

		var n1 Node
		Igen(res, &n1, nil)
		cgen_wb(n, &n1, wb)
		Regfree(&n1)
		return
	}

	// update addressability for string, slice
	// can't do in walk because n->left->addable
	// changes if n->left is an escaping local variable.
	switch n.Op {
	case OSPTR, OLEN:
		if Isslice(n.Left.Type) || Istype(n.Left.Type, TSTRING) {
			n.Addable = n.Left.Addable
		}

	case OCAP:
		if Isslice(n.Left.Type) {
			n.Addable = n.Left.Addable
		}

	case OITAB:
		n.Addable = n.Left.Addable
	}

	if wb {
		if int(Simtype[res.Type.Etype]) != Tptr {
			Fatal("cgen_wb of type %v", res.Type)
		}
		if n.Ullman >= UINF {
			var n1 Node
			Tempname(&n1, n.Type)
			Cgen(n, &n1)
			n = &n1
		}
		cgen_wbptr(n, res)
		return
	}

	// Write barrier now handled. Code below this line can ignore wb.

	if Ctxt.Arch.Thechar == '5' { // TODO(rsc): Maybe more often?
		// if both are addressable, move
		if n.Addable && res.Addable {
			if Is64(n.Type) || Is64(res.Type) || n.Op == OREGISTER || res.Op == OREGISTER || Iscomplex[n.Type.Etype] || Iscomplex[res.Type.Etype] {
				Thearch.Gmove(n, res)
			} else {
				var n1 Node
				Regalloc(&n1, n.Type, nil)
				Thearch.Gmove(n, &n1)
				Cgen(&n1, res)
				Regfree(&n1)
			}

			return
		}

		// if both are not addressable, use a temporary.
		if !n.Addable && !res.Addable {
			// could use regalloc here sometimes,
			// but have to check for ullman >= UINF.
			var n1 Node
			Tempname(&n1, n.Type)
			Cgen(n, &n1)
			Cgen(&n1, res)
			return
		}

		// if result is not addressable directly but n is,
		// compute its address and then store via the address.
		if !res.Addable {
			var n1 Node
			Igen(res, &n1, nil)
			Cgen(n, &n1)
			Regfree(&n1)
			return
		}
	}

	if Complexop(n, res) {
		Complexgen(n, res)
		return
	}

	if (Ctxt.Arch.Thechar == '6' || Ctxt.Arch.Thechar == '8') && n.Addable {
		Thearch.Gmove(n, res)
		return
	}

	if Ctxt.Arch.Thechar == '7' || Ctxt.Arch.Thechar == '9' {
		// if both are addressable, move
		if n.Addable {
			if n.Op == OREGISTER || res.Op == OREGISTER {
				Thearch.Gmove(n, res)
			} else {
				var n1 Node
				Regalloc(&n1, n.Type, nil)
				Thearch.Gmove(n, &n1)
				Cgen(&n1, res)
				Regfree(&n1)
			}
			return
		}
	}

	// if n is sudoaddable generate addr and move
	if Ctxt.Arch.Thechar == '5' && !Is64(n.Type) && !Is64(res.Type) && !Iscomplex[n.Type.Etype] && !Iscomplex[res.Type.Etype] {
		a := Thearch.Optoas(OAS, n.Type)
		var addr obj.Addr
		if Thearch.Sudoaddable(a, n, &addr) {
			if res.Op != OREGISTER {
				var n2 Node
				Regalloc(&n2, res.Type, nil)
				p1 := Thearch.Gins(a, nil, &n2)
				p1.From = addr
				if Debug['g'] != 0 {
					fmt.Printf("%v [ignore previous line]\n", p1)
				}
				Thearch.Gmove(&n2, res)
				Regfree(&n2)
			} else {
				p1 := Thearch.Gins(a, nil, res)
				p1.From = addr
				if Debug['g'] != 0 {
					fmt.Printf("%v [ignore previous line]\n", p1)
				}
			}
			Thearch.Sudoclean()
			return
		}
	}

	nl := n.Left
	nr := n.Right

	if nl != nil && nl.Ullman >= UINF {
		if nr != nil && nr.Ullman >= UINF {
			var n1 Node
			Tempname(&n1, nl.Type)
			Cgen(nl, &n1)
			n2 := *n
			n2.Left = &n1
			Cgen(&n2, res)
			return
		}
	}

	// 64-bit ops are hard on 32-bit machine.
	if Ctxt.Arch.Regsize == 4 && (Is64(n.Type) || Is64(res.Type) || n.Left != nil && Is64(n.Left.Type)) {
		switch n.Op {
		// math goes to cgen64.
		case OMINUS,
			OCOM,
			OADD,
			OSUB,
			OMUL,
			OLROT,
			OLSH,
			ORSH,
			OAND,
			OOR,
			OXOR:
			Thearch.Cgen64(n, res)
			return
		}
	}

	if Thearch.Cgen_float != nil && nl != nil && Isfloat[n.Type.Etype] && Isfloat[nl.Type.Etype] {
		Thearch.Cgen_float(n, res)
		return
	}

	if !Iscomplex[n.Type.Etype] && Ctxt.Arch.Regsize == 8 {
		a := Thearch.Optoas(OAS, n.Type)
		var addr obj.Addr
		if Thearch.Sudoaddable(a, n, &addr) {
			if res.Op == OREGISTER {
				p1 := Thearch.Gins(a, nil, res)
				p1.From = addr
			} else {
				var n2 Node
				Regalloc(&n2, n.Type, nil)
				p1 := Thearch.Gins(a, nil, &n2)
				p1.From = addr
				Thearch.Gins(a, &n2, res)
				Regfree(&n2)
			}

			Thearch.Sudoclean()
			return
		}
	}

	var a int
	switch n.Op {
	default:
		Dump("cgen", n)
		Dump("cgen-res", res)
		Fatal("cgen: unknown op %v", Nconv(n, obj.FmtShort|obj.FmtSign))

	case OOROR, OANDAND,
		OEQ, ONE,
		OLT, OLE,
		OGE, OGT,
		ONOT:
		Bvgen(n, res, true)
		return

	case OPLUS:
		Cgen(nl, res)
		return

		// unary
	case OCOM:
		a := Thearch.Optoas(OXOR, nl.Type)

		var n1 Node
		Regalloc(&n1, nl.Type, nil)
		Cgen(nl, &n1)
		var n2 Node
		Nodconst(&n2, nl.Type, -1)
		Thearch.Gins(a, &n2, &n1)
		cgen_norm(n, &n1, res)
		return

	case OMINUS:
		if Isfloat[nl.Type.Etype] {
			nr = Nodintconst(-1)
			Convlit(&nr, n.Type)
			a = Thearch.Optoas(OMUL, nl.Type)
			goto sbop
		}

		a := Thearch.Optoas(int(n.Op), nl.Type)
		// unary
		var n1 Node
		Regalloc(&n1, nl.Type, res)

		Cgen(nl, &n1)
		if Ctxt.Arch.Thechar == '5' {
			var n2 Node
			Nodconst(&n2, nl.Type, 0)
			Thearch.Gins(a, &n2, &n1)
		} else if Ctxt.Arch.Thechar == '7' {
			Thearch.Gins(a, &n1, &n1)
		} else {
			Thearch.Gins(a, nil, &n1)
		}
		cgen_norm(n, &n1, res)
		return

	case OSQRT:
		var n1 Node
		Regalloc(&n1, nl.Type, res)
		Cgen(n.Left, &n1)
		Thearch.Gins(Thearch.Optoas(OSQRT, nl.Type), &n1, &n1)
		Thearch.Gmove(&n1, res)
		Regfree(&n1)
		return

	case OGETG:
		Thearch.Getg(res)
		return

		// symmetric binary
	case OAND,
		OOR,
		OXOR,
		OADD,
		OMUL:
		if n.Op == OMUL && Thearch.Cgen_bmul != nil && Thearch.Cgen_bmul(int(n.Op), nl, nr, res) {
			break
		}
		a = Thearch.Optoas(int(n.Op), nl.Type)
		goto sbop

		// asymmetric binary
	case OSUB:
		a = Thearch.Optoas(int(n.Op), nl.Type)
		goto abop

	case OHMUL:
		Thearch.Cgen_hmul(nl, nr, res)

	case OCONV:
		if Eqtype(n.Type, nl.Type) || Noconv(n.Type, nl.Type) {
			Cgen(nl, res)
			return
		}

		if Ctxt.Arch.Thechar == '8' {
			var n1 Node
			var n2 Node
			Tempname(&n2, n.Type)
			Mgen(nl, &n1, res)
			Thearch.Gmove(&n1, &n2)
			Thearch.Gmove(&n2, res)
			Mfree(&n1)
			break
		}

		var n1 Node
		var n2 Node
		if Ctxt.Arch.Thechar == '5' {
			if nl.Addable && !Is64(nl.Type) {
				Regalloc(&n1, nl.Type, res)
				Thearch.Gmove(nl, &n1)
			} else {
				if n.Type.Width > int64(Widthptr) || Is64(nl.Type) || Isfloat[nl.Type.Etype] {
					Tempname(&n1, nl.Type)
				} else {
					Regalloc(&n1, nl.Type, res)
				}
				Cgen(nl, &n1)
			}
			if n.Type.Width > int64(Widthptr) || Is64(n.Type) || Isfloat[n.Type.Etype] {
				Tempname(&n2, n.Type)
			} else {
				Regalloc(&n2, n.Type, nil)
			}
		} else {
			if n.Type.Width > nl.Type.Width {
				// If loading from memory, do conversion during load,
				// so as to avoid use of 8-bit register in, say, int(*byteptr).
				switch nl.Op {
				case ODOT, ODOTPTR, OINDEX, OIND, ONAME:
					Igen(nl, &n1, res)
					Regalloc(&n2, n.Type, res)
					Thearch.Gmove(&n1, &n2)
					Thearch.Gmove(&n2, res)
					Regfree(&n2)
					Regfree(&n1)
					return
				}
			}
			Regalloc(&n1, nl.Type, res)
			Regalloc(&n2, n.Type, &n1)
			Cgen(nl, &n1)
		}

		// if we do the conversion n1 -> n2 here
		// reusing the register, then gmove won't
		// have to allocate its own register.
		Thearch.Gmove(&n1, &n2)
		Thearch.Gmove(&n2, res)
		if n2.Op == OREGISTER {
			Regfree(&n2)
		}
		if n1.Op == OREGISTER {
			Regfree(&n1)
		}

	case ODOT,
		ODOTPTR,
		OINDEX,
		OIND,
		ONAME: // PHEAP or PPARAMREF var
		var n1 Node
		Igen(n, &n1, res)

		Thearch.Gmove(&n1, res)
		Regfree(&n1)

		// interface table is first word of interface value
	case OITAB:
		var n1 Node
		Igen(nl, &n1, res)

		n1.Type = n.Type
		Thearch.Gmove(&n1, res)
		Regfree(&n1)

	case OSPTR:
		// pointer is the first word of string or slice.
		if Isconst(nl, CTSTR) {
			var n1 Node
			Regalloc(&n1, Types[Tptr], res)
			p1 := Thearch.Gins(Thearch.Optoas(OAS, n1.Type), nil, &n1)
			Datastring(nl.Val.U.Sval, &p1.From)
			p1.From.Type = obj.TYPE_ADDR
			Thearch.Gmove(&n1, res)
			Regfree(&n1)
			break
		}

		var n1 Node
		Igen(nl, &n1, res)
		n1.Type = n.Type
		Thearch.Gmove(&n1, res)
		Regfree(&n1)

	case OLEN:
		if Istype(nl.Type, TMAP) || Istype(nl.Type, TCHAN) {
			// map and chan have len in the first int-sized word.
			// a zero pointer means zero length
			var n1 Node
			Regalloc(&n1, Types[Tptr], res)

			Cgen(nl, &n1)

			var n2 Node
			Nodconst(&n2, Types[Tptr], 0)
			p1 := Thearch.Ginscmp(OEQ, Types[Tptr], &n1, &n2, 0)

			n2 = n1
			n2.Op = OINDREG
			n2.Type = Types[Simtype[TINT]]
			Thearch.Gmove(&n2, &n1)

			Patch(p1, Pc)

			Thearch.Gmove(&n1, res)
			Regfree(&n1)
			break
		}

		if Istype(nl.Type, TSTRING) || Isslice(nl.Type) {
			// both slice and string have len one pointer into the struct.
			// a zero pointer means zero length
			var n1 Node
			Igen(nl, &n1, res)

			n1.Type = Types[Simtype[TUINT]]
			n1.Xoffset += int64(Array_nel)
			Thearch.Gmove(&n1, res)
			Regfree(&n1)
			break
		}

		Fatal("cgen: OLEN: unknown type %v", Tconv(nl.Type, obj.FmtLong))

	case OCAP:
		if Istype(nl.Type, TCHAN) {
			// chan has cap in the second int-sized word.
			// a zero pointer means zero length
			var n1 Node
			Regalloc(&n1, Types[Tptr], res)

			Cgen(nl, &n1)

			var n2 Node
			Nodconst(&n2, Types[Tptr], 0)
			p1 := Thearch.Ginscmp(OEQ, Types[Tptr], &n1, &n2, 0)

			n2 = n1
			n2.Op = OINDREG
			n2.Xoffset = int64(Widthint)
			n2.Type = Types[Simtype[TINT]]
			Thearch.Gmove(&n2, &n1)

			Patch(p1, Pc)

			Thearch.Gmove(&n1, res)
			Regfree(&n1)
			break
		}

		if Isslice(nl.Type) {
			var n1 Node
			Igen(nl, &n1, res)
			n1.Type = Types[Simtype[TUINT]]
			n1.Xoffset += int64(Array_cap)
			Thearch.Gmove(&n1, res)
			Regfree(&n1)
			break
		}

		Fatal("cgen: OCAP: unknown type %v", Tconv(nl.Type, obj.FmtLong))

	case OADDR:
		if n.Bounded { // let race detector avoid nil checks
			Disable_checknil++
		}
		Agen(nl, res)
		if n.Bounded {
			Disable_checknil--
		}

	case OCALLMETH:
		cgen_callmeth(n, 0)
		cgen_callret(n, res)

	case OCALLINTER:
		cgen_callinter(n, res, 0)
		cgen_callret(n, res)

	case OCALLFUNC:
		cgen_call(n, 0)
		cgen_callret(n, res)

	case OMOD, ODIV:
		if Isfloat[n.Type.Etype] || Thearch.Dodiv == nil {
			a = Thearch.Optoas(int(n.Op), nl.Type)
			goto abop
		}

		if nl.Ullman >= nr.Ullman {
			var n1 Node
			Regalloc(&n1, nl.Type, res)
			Cgen(nl, &n1)
			cgen_div(int(n.Op), &n1, nr, res)
			Regfree(&n1)
		} else {
			var n2 Node
			if !Smallintconst(nr) {
				Regalloc(&n2, nr.Type, res)
				Cgen(nr, &n2)
			} else {
				n2 = *nr
			}

			cgen_div(int(n.Op), nl, &n2, res)
			if n2.Op != OLITERAL {
				Regfree(&n2)
			}
		}

	case OLSH, ORSH, OLROT:
		Thearch.Cgen_shift(int(n.Op), n.Bounded, nl, nr, res)
	}

	return

	/*
	 * put simplest on right - we'll generate into left
	 * and then adjust it using the computation of right.
	 * constants and variables have the same ullman
	 * count, so look for constants specially.
	 *
	 * an integer constant we can use as an immediate
	 * is simpler than a variable - we can use the immediate
	 * in the adjustment instruction directly - so it goes
	 * on the right.
	 *
	 * other constants, like big integers or floating point
	 * constants, require a mov into a register, so those
	 * might as well go on the left, so we can reuse that
	 * register for the computation.
	 */
sbop: // symmetric binary
	if nl.Ullman < nr.Ullman || (nl.Ullman == nr.Ullman && (Smallintconst(nl) || (nr.Op == OLITERAL && !Smallintconst(nr)))) {
		r := nl
		nl = nr
		nr = r
	}

abop: // asymmetric binary
	var n1 Node
	var n2 Node
	if Ctxt.Arch.Thechar == '8' {
		// no registers, sigh
		if Smallintconst(nr) {
			var n1 Node
			Mgen(nl, &n1, res)
			var n2 Node
			Regalloc(&n2, nl.Type, &n1)
			Thearch.Gmove(&n1, &n2)
			Thearch.Gins(a, nr, &n2)
			Thearch.Gmove(&n2, res)
			Regfree(&n2)
			Mfree(&n1)
		} else if nl.Ullman >= nr.Ullman {
			var nt Node
			Tempname(&nt, nl.Type)
			Cgen(nl, &nt)
			var n2 Node
			Mgen(nr, &n2, nil)
			var n1 Node
			Regalloc(&n1, nl.Type, res)
			Thearch.Gmove(&nt, &n1)
			Thearch.Gins(a, &n2, &n1)
			Thearch.Gmove(&n1, res)
			Regfree(&n1)
			Mfree(&n2)
		} else {
			var n2 Node
			Regalloc(&n2, nr.Type, res)
			Cgen(nr, &n2)
			var n1 Node
			Regalloc(&n1, nl.Type, nil)
			Cgen(nl, &n1)
			Thearch.Gins(a, &n2, &n1)
			Regfree(&n2)
			Thearch.Gmove(&n1, res)
			Regfree(&n1)
		}
		return
	}

	if nl.Ullman >= nr.Ullman {
		Regalloc(&n1, nl.Type, res)
		Cgen(nl, &n1)

		if Smallintconst(nr) && Ctxt.Arch.Thechar != '5' && Ctxt.Arch.Thechar != '7' && Ctxt.Arch.Thechar != '9' { // TODO(rsc): Check opcode for arm
			n2 = *nr
		} else {
			Regalloc(&n2, nr.Type, nil)
			Cgen(nr, &n2)
		}
	} else {
		if Smallintconst(nr) && Ctxt.Arch.Thechar != '5' && Ctxt.Arch.Thechar != '7' && Ctxt.Arch.Thechar != '9' { // TODO(rsc): Check opcode for arm
			n2 = *nr
		} else {
			Regalloc(&n2, nr.Type, res)
			Cgen(nr, &n2)
		}

		Regalloc(&n1, nl.Type, nil)
		Cgen(nl, &n1)
	}

	Thearch.Gins(a, &n2, &n1)
	if n2.Op != OLITERAL {
		Regfree(&n2)
	}
	cgen_norm(n, &n1, res)
}

var sys_wbptr *Node

func cgen_wbptr(n, res *Node) {
	if Debug_wb > 0 {
		Warn("write barrier")
	}

	var dst, src Node
	Igen(res, &dst, nil)
	if n.Op == OREGISTER {
		src = *n
		Regrealloc(&src)
	} else {
		Cgenr(n, &src, nil)
	}

	wbEnabled := syslook("writeBarrierEnabled", 0)
	pbr := Thearch.Ginscmp(ONE, Types[TUINT8], wbEnabled, Nodintconst(0), -1)
	Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &src, &dst)
	pjmp := Gbranch(obj.AJMP, nil, 0)
	Patch(pbr, Pc)
	var adst Node
	Agenr(&dst, &adst, &dst)
	p := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &adst, nil)
	a := &p.To
	a.Type = obj.TYPE_MEM
	a.Reg = int16(Thearch.REGSP)
	a.Offset = 0
	if HasLinkRegister() {
		a.Offset += int64(Widthptr)
	}
	p2 := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &src, nil)
	p2.To = p.To
	p2.To.Offset += int64(Widthptr)
	Regfree(&adst)
	if sys_wbptr == nil {
		sys_wbptr = writebarrierfn("writebarrierptr", Types[Tptr], Types[Tptr])
	}
	Ginscall(sys_wbptr, 0)
	Patch(pjmp, Pc)

	Regfree(&dst)
	Regfree(&src)
}

func cgen_wbfat(n, res *Node) {
	if Debug_wb > 0 {
		Warn("write barrier")
	}
	needType := true
	funcName := "typedmemmove"
	var dst, src Node
	if n.Ullman >= res.Ullman {
		Agenr(n, &src, nil)
		Agenr(res, &dst, nil)
	} else {
		Agenr(res, &dst, nil)
		Agenr(n, &src, nil)
	}
	p := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &dst, nil)
	a := &p.To
	a.Type = obj.TYPE_MEM
	a.Reg = int16(Thearch.REGSP)
	a.Offset = 0
	if HasLinkRegister() {
		a.Offset += int64(Widthptr)
	}
	if needType {
		a.Offset += int64(Widthptr)
	}
	p2 := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &src, nil)
	p2.To = p.To
	p2.To.Offset += int64(Widthptr)
	Regfree(&dst)
	if needType {
		src.Type = Types[Tptr]
		Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), typename(n.Type), &src)
		p3 := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &src, nil)
		p3.To = p2.To
		p3.To.Offset -= 2 * int64(Widthptr)
	}
	Regfree(&src)
	Ginscall(writebarrierfn(funcName, Types[Tptr], Types[Tptr]), 0)
}

// cgen_norm moves n1 to res, truncating to expected type if necessary.
// n1 is a register, and cgen_norm frees it.
func cgen_norm(n, n1, res *Node) {
	switch Ctxt.Arch.Thechar {
	case '6', '8':
		// We use sized math, so the result is already truncated.
	default:
		switch n.Op {
		case OADD, OSUB, OMUL, ODIV, OCOM, OMINUS:
			// TODO(rsc): What about left shift?
			Thearch.Gins(Thearch.Optoas(OAS, n.Type), n1, n1)
		}
	}

	Thearch.Gmove(n1, res)
	Regfree(n1)
}

func Mgen(n *Node, n1 *Node, rg *Node) {
	n1.Op = OEMPTY

	if n.Addable {
		*n1 = *n
		if n1.Op == OREGISTER || n1.Op == OINDREG {
			reg[n.Reg-int16(Thearch.REGMIN)]++
		}
		return
	}

	Tempname(n1, n.Type)
	Cgen(n, n1)
	if n.Type.Width <= int64(Widthptr) || Isfloat[n.Type.Etype] {
		n2 := *n1
		Regalloc(n1, n.Type, rg)
		Thearch.Gmove(&n2, n1)
	}
}

func Mfree(n *Node) {
	if n.Op == OREGISTER {
		Regfree(n)
	}
}

/*
 * allocate a register (reusing res if possible) and generate
 *  a = n
 * The caller must call Regfree(a).
 */
func Cgenr(n *Node, a *Node, res *Node) {
	if Debug['g'] != 0 {
		Dump("cgenr-n", n)
	}

	if Isfat(n.Type) {
		Fatal("cgenr on fat node")
	}

	if n.Addable {
		Regalloc(a, n.Type, res)
		Thearch.Gmove(n, a)
		return
	}

	switch n.Op {
	case ONAME,
		ODOT,
		ODOTPTR,
		OINDEX,
		OCALLFUNC,
		OCALLMETH,
		OCALLINTER:
		var n1 Node
		Igen(n, &n1, res)
		Regalloc(a, Types[Tptr], &n1)
		Thearch.Gmove(&n1, a)
		Regfree(&n1)

	default:
		Regalloc(a, n.Type, res)
		Cgen(n, a)
	}
}

/*
 * allocate a register (reusing res if possible) and generate
 * a = &n
 * The caller must call Regfree(a).
 * The generated code checks that the result is not nil.
 */
func Agenr(n *Node, a *Node, res *Node) {
	if Debug['g'] != 0 {
		Dump("\nagenr-n", n)
	}

	nl := n.Left
	nr := n.Right

	switch n.Op {
	case ODOT, ODOTPTR, OCALLFUNC, OCALLMETH, OCALLINTER:
		var n1 Node
		Igen(n, &n1, res)
		Regalloc(a, Types[Tptr], &n1)
		Agen(&n1, a)
		Regfree(&n1)

	case OIND:
		Cgenr(n.Left, a, res)
		Cgen_checknil(a)

	case OINDEX:
		if Ctxt.Arch.Thechar == '5' {
			var p2 *obj.Prog // to be patched to panicindex.
			w := uint32(n.Type.Width)
			bounded := Debug['B'] != 0 || n.Bounded
			var n1 Node
			var n3 Node
			if nr.Addable {
				var tmp Node
				if !Isconst(nr, CTINT) {
					Tempname(&tmp, Types[TINT32])
				}
				if !Isconst(nl, CTSTR) {
					Agenr(nl, &n3, res)
				}
				if !Isconst(nr, CTINT) {
					p2 = Thearch.Cgenindex(nr, &tmp, bounded)
					Regalloc(&n1, tmp.Type, nil)
					Thearch.Gmove(&tmp, &n1)
				}
			} else if nl.Addable {
				if !Isconst(nr, CTINT) {
					var tmp Node
					Tempname(&tmp, Types[TINT32])
					p2 = Thearch.Cgenindex(nr, &tmp, bounded)
					Regalloc(&n1, tmp.Type, nil)
					Thearch.Gmove(&tmp, &n1)
				}

				if !Isconst(nl, CTSTR) {
					Agenr(nl, &n3, res)
				}
			} else {
				var tmp Node
				Tempname(&tmp, Types[TINT32])
				p2 = Thearch.Cgenindex(nr, &tmp, bounded)
				nr = &tmp
				if !Isconst(nl, CTSTR) {
					Agenr(nl, &n3, res)
				}
				Regalloc(&n1, tmp.Type, nil)
				Thearch.Gins(Thearch.Optoas(OAS, tmp.Type), &tmp, &n1)
			}

			// &a is in &n3 (allocated in res)
			// i is in &n1 (if not constant)
			// w is width

			// constant index
			if Isconst(nr, CTINT) {
				if Isconst(nl, CTSTR) {
					Fatal("constant string constant index")
				}
				v := uint64(Mpgetfix(nr.Val.U.Xval))
				var n2 Node
				if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
					if Debug['B'] == 0 && !n.Bounded {
						n1 = n3
						n1.Op = OINDREG
						n1.Type = Types[Tptr]
						n1.Xoffset = int64(Array_nel)
						Nodconst(&n2, Types[TUINT32], int64(v))
						p1 := Thearch.Ginscmp(OGT, Types[TUINT32], &n1, &n2, +1)
						Ginscall(Panicindex, -1)
						Patch(p1, Pc)
					}

					n1 = n3
					n1.Op = OINDREG
					n1.Type = Types[Tptr]
					n1.Xoffset = int64(Array_array)
					Thearch.Gmove(&n1, &n3)
				}

				Nodconst(&n2, Types[Tptr], int64(v*uint64(w)))
				Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n3)
				*a = n3
				break
			}

			var n2 Node
			Regalloc(&n2, Types[TINT32], &n1) // i
			Thearch.Gmove(&n1, &n2)
			Regfree(&n1)

			var n4 Node
			if Debug['B'] == 0 && !n.Bounded {
				// check bounds
				if Isconst(nl, CTSTR) {
					Nodconst(&n4, Types[TUINT32], int64(len(nl.Val.U.Sval)))
				} else if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
					n1 = n3
					n1.Op = OINDREG
					n1.Type = Types[Tptr]
					n1.Xoffset = int64(Array_nel)
					Regalloc(&n4, Types[TUINT32], nil)
					Thearch.Gmove(&n1, &n4)
				} else {
					Nodconst(&n4, Types[TUINT32], nl.Type.Bound)
				}
				p1 := Thearch.Ginscmp(OLT, Types[TUINT32], &n2, &n4, +1)
				if n4.Op == OREGISTER {
					Regfree(&n4)
				}
				if p2 != nil {
					Patch(p2, Pc)
				}
				Ginscall(Panicindex, -1)
				Patch(p1, Pc)
			}

			if Isconst(nl, CTSTR) {
				Regalloc(&n3, Types[Tptr], res)
				p1 := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), nil, &n3)
				Datastring(nl.Val.U.Sval, &p1.From)
				p1.From.Type = obj.TYPE_ADDR
			} else if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
				n1 = n3
				n1.Op = OINDREG
				n1.Type = Types[Tptr]
				n1.Xoffset = int64(Array_array)
				Thearch.Gmove(&n1, &n3)
			}

			if w == 0 {
				// nothing to do
			} else if Thearch.AddIndex != nil && Thearch.AddIndex(&n2, int64(w), &n3) {
				// done by back end
			} else if w == 1 {
				Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n3)
			} else {
				if w&(w-1) == 0 {
					// Power of 2.  Use shift.
					Thearch.Ginscon(Thearch.Optoas(OLSH, Types[TUINT32]), int64(log2(uint64(w))), &n2)
				} else {
					// Not a power of 2.  Use multiply.
					Regalloc(&n4, Types[TUINT32], nil)
					Nodconst(&n1, Types[TUINT32], int64(w))
					Thearch.Gmove(&n1, &n4)
					Thearch.Gins(Thearch.Optoas(OMUL, Types[TUINT32]), &n4, &n2)
					Regfree(&n4)
				}
				Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n3)
			}
			*a = n3
			Regfree(&n2)
			break
		}
		if Ctxt.Arch.Thechar == '8' {
			var p2 *obj.Prog // to be patched to panicindex.
			w := uint32(n.Type.Width)
			bounded := Debug['B'] != 0 || n.Bounded
			var n3 Node
			var tmp Node
			var n1 Node
			if nr.Addable {
				// Generate &nl first, and move nr into register.
				if !Isconst(nl, CTSTR) {
					Igen(nl, &n3, res)
				}
				if !Isconst(nr, CTINT) {
					p2 = Thearch.Igenindex(nr, &tmp, bounded)
					Regalloc(&n1, tmp.Type, nil)
					Thearch.Gmove(&tmp, &n1)
				}
			} else if nl.Addable {
				// Generate nr first, and move &nl into register.
				if !Isconst(nr, CTINT) {
					p2 = Thearch.Igenindex(nr, &tmp, bounded)
					Regalloc(&n1, tmp.Type, nil)
					Thearch.Gmove(&tmp, &n1)
				}

				if !Isconst(nl, CTSTR) {
					Igen(nl, &n3, res)
				}
			} else {
				p2 = Thearch.Igenindex(nr, &tmp, bounded)
				nr = &tmp
				if !Isconst(nl, CTSTR) {
					Igen(nl, &n3, res)
				}
				Regalloc(&n1, tmp.Type, nil)
				Thearch.Gins(Thearch.Optoas(OAS, tmp.Type), &tmp, &n1)
			}

			// For fixed array we really want the pointer in n3.
			var n2 Node
			if Isfixedarray(nl.Type) {
				Regalloc(&n2, Types[Tptr], &n3)
				Agen(&n3, &n2)
				Regfree(&n3)
				n3 = n2
			}

			// &a[0] is in n3 (allocated in res)
			// i is in n1 (if not constant)
			// len(a) is in nlen (if needed)
			// w is width

			// constant index
			if Isconst(nr, CTINT) {
				if Isconst(nl, CTSTR) {
					Fatal("constant string constant index") // front end should handle
				}
				v := uint64(Mpgetfix(nr.Val.U.Xval))
				if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
					if Debug['B'] == 0 && !n.Bounded {
						nlen := n3
						nlen.Type = Types[TUINT32]
						nlen.Xoffset += int64(Array_nel)
						Nodconst(&n2, Types[TUINT32], int64(v))
						p1 := Thearch.Ginscmp(OGT, Types[TUINT32], &nlen, &n2, +1)
						Ginscall(Panicindex, -1)
						Patch(p1, Pc)
					}
				}

				// Load base pointer in n2 = n3.
				Regalloc(&n2, Types[Tptr], &n3)

				n3.Type = Types[Tptr]
				n3.Xoffset += int64(Array_array)
				Thearch.Gmove(&n3, &n2)
				Regfree(&n3)
				if v*uint64(w) != 0 {
					Nodconst(&n1, Types[Tptr], int64(v*uint64(w)))
					Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n1, &n2)
				}
				*a = n2
				break
			}

			// i is in register n1, extend to 32 bits.
			t := Types[TUINT32]

			if Issigned[n1.Type.Etype] {
				t = Types[TINT32]
			}

			Regalloc(&n2, t, &n1) // i
			Thearch.Gmove(&n1, &n2)
			Regfree(&n1)

			if Debug['B'] == 0 && !n.Bounded {
				// check bounds
				t := Types[TUINT32]

				var nlen Node
				if Isconst(nl, CTSTR) {
					Nodconst(&nlen, t, int64(len(nl.Val.U.Sval)))
				} else if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
					nlen = n3
					nlen.Type = t
					nlen.Xoffset += int64(Array_nel)
				} else {
					Nodconst(&nlen, t, nl.Type.Bound)
				}

				p1 := Thearch.Ginscmp(OLT, t, &n2, &nlen, +1)
				if p2 != nil {
					Patch(p2, Pc)
				}
				Ginscall(Panicindex, -1)
				Patch(p1, Pc)
			}

			if Isconst(nl, CTSTR) {
				Regalloc(&n3, Types[Tptr], res)
				p1 := Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), nil, &n3)
				Datastring(nl.Val.U.Sval, &p1.From)
				p1.From.Type = obj.TYPE_ADDR
				Thearch.Gins(Thearch.Optoas(OADD, n3.Type), &n2, &n3)
				goto indexdone1
			}

			// Load base pointer in n3.
			Regalloc(&tmp, Types[Tptr], &n3)

			if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
				n3.Type = Types[Tptr]
				n3.Xoffset += int64(Array_array)
				Thearch.Gmove(&n3, &tmp)
			}

			Regfree(&n3)
			n3 = tmp

			if w == 0 {
				// nothing to do
			} else if Thearch.AddIndex != nil && Thearch.AddIndex(&n2, int64(w), &n3) {
				// done by back end
			} else if w == 1 {
				Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n3)
			} else {
				if w&(w-1) == 0 {
					// Power of 2.  Use shift.
					Thearch.Ginscon(Thearch.Optoas(OLSH, Types[TUINT32]), int64(log2(uint64(w))), &n2)
				} else {
					// Not a power of 2.  Use multiply.
					Thearch.Ginscon(Thearch.Optoas(OMUL, Types[TUINT32]), int64(w), &n2)
				}
				Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n3)
			}

		indexdone1:
			*a = n3
			Regfree(&n2)
			break
		}

		freelen := 0
		w := uint64(n.Type.Width)

		// Generate the non-addressable child first.
		var n3 Node
		var nlen Node
		var tmp Node
		var n1 Node
		if nr.Addable {
			goto irad
		}
		if nl.Addable {
			Cgenr(nr, &n1, nil)
			if !Isconst(nl, CTSTR) {
				if Isfixedarray(nl.Type) {
					Agenr(nl, &n3, res)
				} else {
					Igen(nl, &nlen, res)
					freelen = 1
					nlen.Type = Types[Tptr]
					nlen.Xoffset += int64(Array_array)
					Regalloc(&n3, Types[Tptr], res)
					Thearch.Gmove(&nlen, &n3)
					nlen.Type = Types[Simtype[TUINT]]
					nlen.Xoffset += int64(Array_nel) - int64(Array_array)
				}
			}

			goto index
		}

		Tempname(&tmp, nr.Type)
		Cgen(nr, &tmp)
		nr = &tmp

	irad:
		if !Isconst(nl, CTSTR) {
			if Isfixedarray(nl.Type) {
				Agenr(nl, &n3, res)
			} else {
				if !nl.Addable {
					if res != nil && res.Op == OREGISTER { // give up res, which we don't need yet.
						Regfree(res)
					}

					// igen will need an addressable node.
					var tmp2 Node
					Tempname(&tmp2, nl.Type)
					Cgen(nl, &tmp2)
					nl = &tmp2

					if res != nil && res.Op == OREGISTER { // reacquire res
						Regrealloc(res)
					}
				}

				Igen(nl, &nlen, res)
				freelen = 1
				nlen.Type = Types[Tptr]
				nlen.Xoffset += int64(Array_array)
				Regalloc(&n3, Types[Tptr], res)
				Thearch.Gmove(&nlen, &n3)
				nlen.Type = Types[Simtype[TUINT]]
				nlen.Xoffset += int64(Array_nel) - int64(Array_array)
			}
		}

		if !Isconst(nr, CTINT) {
			Cgenr(nr, &n1, nil)
		}

		goto index

		// &a is in &n3 (allocated in res)
		// i is in &n1 (if not constant)
		// len(a) is in nlen (if needed)
		// w is width

		// constant index
	index:
		if Isconst(nr, CTINT) {
			if Isconst(nl, CTSTR) {
				Fatal("constant string constant index") // front end should handle
			}
			v := uint64(Mpgetfix(nr.Val.U.Xval))
			if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
				if Debug['B'] == 0 && !n.Bounded {
					p1 := Thearch.Ginscmp(OGT, Types[Simtype[TUINT]], &nlen, Nodintconst(int64(v)), +1)
					Ginscall(Panicindex, -1)
					Patch(p1, Pc)
				}

				Regfree(&nlen)
			}

			if v*w != 0 {
				Thearch.Ginscon(Thearch.Optoas(OADD, Types[Tptr]), int64(v*w), &n3)
			}
			*a = n3
			break
		}

		// type of the index
		t := Types[TUINT64]

		if Issigned[n1.Type.Etype] {
			t = Types[TINT64]
		}

		var n2 Node
		Regalloc(&n2, t, &n1) // i
		Thearch.Gmove(&n1, &n2)
		Regfree(&n1)

		if Debug['B'] == 0 && !n.Bounded {
			// check bounds
			t = Types[Simtype[TUINT]]

			if Is64(nr.Type) {
				t = Types[TUINT64]
			}
			if Isconst(nl, CTSTR) {
				Nodconst(&nlen, t, int64(len(nl.Val.U.Sval)))
			} else if Isslice(nl.Type) || nl.Type.Etype == TSTRING {
				// nlen already initialized
			} else {
				Nodconst(&nlen, t, nl.Type.Bound)
			}

			p1 := Thearch.Ginscmp(OLT, t, &n2, &nlen, +1)
			Ginscall(Panicindex, -1)
			Patch(p1, Pc)
		}

		if Isconst(nl, CTSTR) {
			Regalloc(&n3, Types[Tptr], res)
			p1 := Thearch.Gins(Thearch.Optoas(OAS, n3.Type), nil, &n3) // XXX was LEAQ!
			Datastring(nl.Val.U.Sval, &p1.From)
			p1.From.Type = obj.TYPE_ADDR
			Thearch.Gins(Thearch.Optoas(OADD, n3.Type), &n2, &n3)
			goto indexdone
		}

		if w == 0 {
			// nothing to do
		} else if Thearch.AddIndex != nil && Thearch.AddIndex(&n2, int64(w), &n3) {
			// done by back end
		} else if w == 1 {
			Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n3)
		} else {
			if w&(w-1) == 0 {
				// Power of 2.  Use shift.
				Thearch.Ginscon(Thearch.Optoas(OLSH, t), int64(log2(w)), &n2)
			} else {
				// Not a power of 2.  Use multiply.
				Thearch.Ginscon(Thearch.Optoas(OMUL, t), int64(w), &n2)
			}
			Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n3)
		}

	indexdone:
		*a = n3
		Regfree(&n2)
		if freelen != 0 {
			Regfree(&nlen)
		}

	default:
		Regalloc(a, Types[Tptr], res)
		Agen(n, a)
	}
}

// log2 returns the logarithm base 2 of n.  n must be a power of 2.
func log2(n uint64) int {
	x := 0
	for n>>uint(x) != 1 {
		x++
	}
	return x
}

/*
 * generate:
 *	res = &n;
 * The generated code checks that the result is not nil.
 */
func Agen(n *Node, res *Node) {
	if Debug['g'] != 0 {
		Dump("\nagen-res", res)
		Dump("agen-r", n)
	}

	if n == nil || n.Type == nil {
		return
	}

	for n.Op == OCONVNOP {
		n = n.Left
	}

	if Isconst(n, CTNIL) && n.Type.Width > int64(Widthptr) {
		// Use of a nil interface or nil slice.
		// Create a temporary we can take the address of and read.
		// The generated code is just going to panic, so it need not
		// be terribly efficient. See issue 3670.
		var n1 Node
		Tempname(&n1, n.Type)

		Gvardef(&n1)
		Thearch.Clearfat(&n1)
		var n2 Node
		Regalloc(&n2, Types[Tptr], res)
		var n3 Node
		n3.Op = OADDR
		n3.Left = &n1
		Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &n3, &n2)
		Thearch.Gmove(&n2, res)
		Regfree(&n2)
		return
	}

	if n.Op == OINDREG && n.Xoffset == 0 {
		// Generate MOVW R0, R1 instead of MOVW $0(R0), R1.
		// This allows better move propagation in the back ends
		// (and maybe it helps the processor).
		n1 := *n
		n1.Op = OREGISTER
		n1.Type = res.Type
		Thearch.Gmove(&n1, res)
		return
	}

	if n.Addable {
		if n.Op == OREGISTER {
			Fatal("agen OREGISTER")
		}
		var n1 Node
		n1.Op = OADDR
		n1.Left = n
		var n2 Node
		Regalloc(&n2, Types[Tptr], res)
		Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &n1, &n2)
		Thearch.Gmove(&n2, res)
		Regfree(&n2)
		return
	}

	nl := n.Left

	switch n.Op {
	default:
		Fatal("agen: unknown op %v", Nconv(n, obj.FmtShort|obj.FmtSign))

	case OCALLMETH:
		cgen_callmeth(n, 0)
		cgen_aret(n, res)

	case OCALLINTER:
		cgen_callinter(n, res, 0)
		cgen_aret(n, res)

	case OCALLFUNC:
		cgen_call(n, 0)
		cgen_aret(n, res)

	case OEFACE, ODOTTYPE, OSLICE, OSLICEARR, OSLICESTR, OSLICE3, OSLICE3ARR:
		var n1 Node
		Tempname(&n1, n.Type)
		Cgen(n, &n1)
		Agen(&n1, res)

	case OINDEX:
		var n1 Node
		Agenr(n, &n1, res)
		Thearch.Gmove(&n1, res)
		Regfree(&n1)

	case ONAME:
		// should only get here with names in this func.
		if n.Funcdepth > 0 && n.Funcdepth != Funcdepth {
			Dump("bad agen", n)
			Fatal("agen: bad ONAME funcdepth %d != %d", n.Funcdepth, Funcdepth)
		}

		// should only get here for heap vars or paramref
		if n.Class&PHEAP == 0 && n.Class != PPARAMREF {
			Dump("bad agen", n)
			Fatal("agen: bad ONAME class %#x", n.Class)
		}

		Cgen(n.Heapaddr, res)
		if n.Xoffset != 0 {
			addOffset(res, n.Xoffset)
		}

	case OIND:
		Cgen(nl, res)
		Cgen_checknil(res)

	case ODOT:
		Agen(nl, res)
		if n.Xoffset != 0 {
			addOffset(res, n.Xoffset)
		}

	case ODOTPTR:
		Cgen(nl, res)
		Cgen_checknil(res)
		if n.Xoffset != 0 {
			addOffset(res, n.Xoffset)
		}
	}
}

func addOffset(res *Node, offset int64) {
	if Ctxt.Arch.Thechar == '6' || Ctxt.Arch.Thechar == '8' {
		Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), Nodintconst(offset), res)
		return
	}

	var n1, n2 Node
	Regalloc(&n1, Types[Tptr], nil)
	Thearch.Gmove(res, &n1)
	Regalloc(&n2, Types[Tptr], nil)
	Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), Nodintconst(offset), &n2)
	Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &n2, &n1)
	Thearch.Gmove(&n1, res)
	Regfree(&n1)
	Regfree(&n2)
}

// Igen computes the address &n, stores it in a register r,
// and rewrites a to refer to *r. The chosen r may be the
// stack pointer, it may be borrowed from res, or it may
// be a newly allocated register. The caller must call Regfree(a)
// to free r when the address is no longer needed.
// The generated code ensures that &n is not nil.
func Igen(n *Node, a *Node, res *Node) {
	if Debug['g'] != 0 {
		Dump("\nigen-n", n)
	}

	switch n.Op {
	case ONAME:
		if (n.Class&PHEAP != 0) || n.Class == PPARAMREF {
			break
		}
		*a = *n
		return

	case OINDREG:
		// Increase the refcount of the register so that igen's caller
		// has to call Regfree.
		if n.Reg != int16(Thearch.REGSP) {
			reg[n.Reg-int16(Thearch.REGMIN)]++
		}
		*a = *n
		return

	case ODOT:
		Igen(n.Left, a, res)
		a.Xoffset += n.Xoffset
		a.Type = n.Type
		Fixlargeoffset(a)
		return

	case ODOTPTR:
		Cgenr(n.Left, a, res)
		Cgen_checknil(a)
		a.Op = OINDREG
		a.Xoffset += n.Xoffset
		a.Type = n.Type
		Fixlargeoffset(a)
		return

	case OCALLFUNC, OCALLMETH, OCALLINTER:
		switch n.Op {
		case OCALLFUNC:
			cgen_call(n, 0)

		case OCALLMETH:
			cgen_callmeth(n, 0)

		case OCALLINTER:
			cgen_callinter(n, nil, 0)
		}

		var flist Iter
		fp := Structfirst(&flist, Getoutarg(n.Left.Type))
		*a = Node{}
		a.Op = OINDREG
		a.Reg = int16(Thearch.REGSP)
		a.Addable = true
		a.Xoffset = fp.Width
		if HasLinkRegister() {
			a.Xoffset += int64(Ctxt.Arch.Ptrsize)
		}
		a.Type = n.Type
		return

		// Index of fixed-size array by constant can
	// put the offset in the addressing.
	// Could do the same for slice except that we need
	// to use the real index for the bounds checking.
	case OINDEX:
		if Isfixedarray(n.Left.Type) || (Isptr[n.Left.Type.Etype] && Isfixedarray(n.Left.Left.Type)) {
			if Isconst(n.Right, CTINT) {
				// Compute &a.
				if !Isptr[n.Left.Type.Etype] {
					Igen(n.Left, a, res)
				} else {
					var n1 Node
					Igen(n.Left, &n1, res)
					Cgen_checknil(&n1)
					Regalloc(a, Types[Tptr], res)
					Thearch.Gmove(&n1, a)
					Regfree(&n1)
					a.Op = OINDREG
				}

				// Compute &a[i] as &a + i*width.
				a.Type = n.Type

				a.Xoffset += Mpgetfix(n.Right.Val.U.Xval) * n.Type.Width
				Fixlargeoffset(a)
				return
			}
		}
	}

	Agenr(n, a, res)
	a.Op = OINDREG
	a.Type = n.Type
}

// Bgen generates code for branches:
//
// 	if n == wantTrue {
// 		goto to
// 	}
func Bgen(n *Node, wantTrue bool, likely int, to *obj.Prog) {
	bgenx(n, nil, wantTrue, likely, to)
}

// Bvgen generates code for calculating boolean values:
// 	res = n == wantTrue
func Bvgen(n, res *Node, wantTrue bool) {
	if Thearch.Ginsboolval == nil {
		// Direct value generation not implemented for this architecture.
		// Implement using jumps.
		bvgenjump(n, res, wantTrue, true)
		return
	}
	bgenx(n, res, wantTrue, 0, nil)
}

// bvgenjump implements boolean value generation using jumps:
// 	if n == wantTrue {
// 		res = 1
// 	} else {
// 		res = 0
// 	}
// geninit controls whether n's Ninit is generated.
func bvgenjump(n, res *Node, wantTrue, geninit bool) {
	init := n.Ninit
	if !geninit {
		n.Ninit = nil
	}
	p1 := Gbranch(obj.AJMP, nil, 0)
	p2 := Pc
	Thearch.Gmove(Nodbool(true), res)
	p3 := Gbranch(obj.AJMP, nil, 0)
	Patch(p1, Pc)
	Bgen(n, wantTrue, 0, p2)
	Thearch.Gmove(Nodbool(false), res)
	Patch(p3, Pc)
	n.Ninit = init
}

// bgenx is the backend for Bgen and Bvgen.
// If res is nil, it generates a branch.
// Otherwise, it generates a boolean value.
func bgenx(n, res *Node, wantTrue bool, likely int, to *obj.Prog) {
	if Debug['g'] != 0 {
		fmt.Printf("\nbgenx wantTrue=%t likely=%d to=%v\n", wantTrue, likely, to)
		Dump("n", n)
		Dump("res", res)
	}

	genval := res != nil

	if n == nil {
		n = Nodbool(true)
	}

	Genlist(n.Ninit)

	if n.Type == nil {
		Convlit(&n, Types[TBOOL])
		if n.Type == nil {
			return
		}
	}

	if n.Type.Etype != TBOOL {
		Fatal("bgen: bad type %v for %v", n.Type, Oconv(int(n.Op), 0))
	}

	for n.Op == OCONVNOP {
		n = n.Left
		Genlist(n.Ninit)
	}

	if Thearch.Bgen_float != nil && n.Left != nil && Isfloat[n.Left.Type.Etype] {
		if genval {
			bvgenjump(n, res, wantTrue, false)
			return
		}
		Thearch.Bgen_float(n, wantTrue, likely, to)
		return
	}

	switch n.Op {
	default:
		if genval {
			Cgen(n, res)
			if !wantTrue {
				Thearch.Gins(Thearch.Optoas(OXOR, Types[TUINT8]), Nodintconst(1), res)
			}
			return
		}

		var tmp Node
		Regalloc(&tmp, n.Type, nil)
		Cgen(n, &tmp)
		bgenNonZero(&tmp, nil, wantTrue, likely, to)
		Regfree(&tmp)
		return

	case ONAME:
		if genval {
			// 5g, 7g, and 9g might need a temporary or other help here,
			// but they don't support direct generation of a bool value yet.
			// We can fix that as we go.
			switch Ctxt.Arch.Thechar {
			case '5', '7', '9':
				Fatal("genval 5g, 7g, 9g ONAMES not fully implemented")
			}
			Cgen(n, res)
			if !wantTrue {
				Thearch.Gins(Thearch.Optoas(OXOR, Types[TUINT8]), Nodintconst(1), res)
			}
			return
		}

		if n.Addable && Ctxt.Arch.Thechar != '5' && Ctxt.Arch.Thechar != '7' && Ctxt.Arch.Thechar != '9' {
			// no need for a temporary
			bgenNonZero(n, nil, wantTrue, likely, to)
			return
		}
		var tmp Node
		Regalloc(&tmp, n.Type, nil)
		Cgen(n, &tmp)
		bgenNonZero(&tmp, nil, wantTrue, likely, to)
		Regfree(&tmp)
		return

	case OLITERAL:
		// n is a constant.
		if !Isconst(n, CTBOOL) {
			Fatal("bgen: non-bool const %v\n", Nconv(n, obj.FmtLong))
		}
		if genval {
			Cgen(Nodbool(wantTrue == n.Val.U.Bval), res)
			return
		}
		// If n == wantTrue, jump; otherwise do nothing.
		if wantTrue == n.Val.U.Bval {
			Patch(Gbranch(obj.AJMP, nil, likely), to)
		}
		return

	case OANDAND, OOROR:
		and := (n.Op == OANDAND) == wantTrue
		if genval {
			p1 := Gbranch(obj.AJMP, nil, 0)
			p2 := Gbranch(obj.AJMP, nil, 0)
			Patch(p2, Pc)
			Cgen(Nodbool(!and), res)
			p3 := Gbranch(obj.AJMP, nil, 0)
			Patch(p1, Pc)
			Bgen(n.Left, wantTrue != and, 0, p2)
			Bvgen(n.Right, res, wantTrue)
			Patch(p3, Pc)
			return
		}

		if and {
			p1 := Gbranch(obj.AJMP, nil, 0)
			p2 := Gbranch(obj.AJMP, nil, 0)
			Patch(p1, Pc)
			Bgen(n.Left, !wantTrue, -likely, p2)
			Bgen(n.Right, !wantTrue, -likely, p2)
			p1 = Gbranch(obj.AJMP, nil, 0)
			Patch(p1, to)
			Patch(p2, Pc)
		} else {
			Bgen(n.Left, wantTrue, likely, to)
			Bgen(n.Right, wantTrue, likely, to)
		}
		return

	case ONOT: // unary
		if n.Left == nil || n.Left.Type == nil {
			return
		}
		bgenx(n.Left, res, !wantTrue, likely, to)
		return

	case OEQ, ONE, OLT, OGT, OLE, OGE:
		if n.Left == nil || n.Left.Type == nil || n.Right == nil || n.Right.Type == nil {
			return
		}
	}

	// n.Op is one of OEQ, ONE, OLT, OGT, OLE, OGE
	nl := n.Left
	nr := n.Right
	a := int(n.Op)

	if !wantTrue {
		if Isfloat[nr.Type.Etype] {
			// Brcom is not valid on floats when NaN is involved.
			ll := n.Ninit // avoid re-genning Ninit
			n.Ninit = nil
			if genval {
				bgenx(n, res, true, likely, to)
				Thearch.Gins(Thearch.Optoas(OXOR, Types[TUINT8]), Nodintconst(1), res) // res = !res
				n.Ninit = ll
				return
			}
			p1 := Gbranch(obj.AJMP, nil, 0)
			p2 := Gbranch(obj.AJMP, nil, 0)
			Patch(p1, Pc)
			bgenx(n, res, true, -likely, p2)
			Patch(Gbranch(obj.AJMP, nil, 0), to)
			Patch(p2, Pc)
			n.Ninit = ll
			return
		}

		a = Brcom(a)
	}
	wantTrue = true

	// make simplest on right
	if nl.Op == OLITERAL || (nl.Ullman < nr.Ullman && nl.Ullman < UINF) {
		a = Brrev(a)
		nl, nr = nr, nl
	}

	if Isslice(nl.Type) || Isinter(nl.Type) {
		// front end should only leave cmp to literal nil
		if (a != OEQ && a != ONE) || nr.Op != OLITERAL {
			if Isslice(nl.Type) {
				Yyerror("illegal slice comparison")
			} else {
				Yyerror("illegal interface comparison")
			}
			return
		}

		var ptr Node
		Igen(nl, &ptr, nil)
		if Isslice(nl.Type) {
			ptr.Xoffset += int64(Array_array)
		}
		ptr.Type = Types[Tptr]
		var tmp Node
		Regalloc(&tmp, ptr.Type, &ptr)
		Cgen(&ptr, &tmp)
		Regfree(&ptr)
		bgenNonZero(&tmp, res, a == OEQ != wantTrue, likely, to)
		Regfree(&tmp)
		return
	}

	if Iscomplex[nl.Type.Etype] {
		complexbool(a, nl, nr, res, wantTrue, likely, to)
		return
	}

	if Ctxt.Arch.Regsize == 4 && Is64(nr.Type) {
		if genval {
			// TODO: Teach Cmp64 to generate boolean values and remove this.
			bvgenjump(n, res, wantTrue, false)
			return
		}
		if !nl.Addable || Isconst(nl, CTINT) {
			nl = CgenTemp(nl)
		}
		if !nr.Addable {
			nr = CgenTemp(nr)
		}
		Thearch.Cmp64(nl, nr, a, likely, to)
		return
	}

	if nr.Ullman >= UINF {
		var n1 Node
		Regalloc(&n1, nl.Type, nil)
		Cgen(nl, &n1)

		var tmp Node
		Tempname(&tmp, nl.Type)
		Thearch.Gmove(&n1, &tmp)
		Regfree(&n1)

		var n2 Node
		Regalloc(&n2, nr.Type, nil)
		Cgen(nr, &n2)
		Regfree(&n2)

		Regalloc(&n1, nl.Type, nil)
		Cgen(&tmp, &n1)
		Regfree(&n1)
	} else {
		var n1 Node
		if !nl.Addable && Ctxt.Arch.Thechar == '8' {
			Tempname(&n1, nl.Type)
		} else {
			Regalloc(&n1, nl.Type, nil)
			defer Regfree(&n1)
		}
		Cgen(nl, &n1)
		nl = &n1

		if Smallintconst(nr) && Ctxt.Arch.Thechar != '9' {
			Thearch.Gins(Thearch.Optoas(OCMP, nr.Type), nl, nr)
			bins(nr.Type, res, a, likely, to)
			return
		}

		if !nr.Addable && Ctxt.Arch.Thechar == '8' {
			nr = CgenTemp(nr)
		}

		var n2 Node
		Regalloc(&n2, nr.Type, nil)
		Cgen(nr, &n2)
		nr = &n2
		Regfree(&n2)
	}

	l, r := nl, nr

	// On x86, only < and <= work right with NaN; reverse if needed
	if Ctxt.Arch.Thechar == '6' && Isfloat[nl.Type.Etype] && (a == OGT || a == OGE) {
		l, r = r, l
		a = Brrev(a)
	}

	// Do the comparison.
	Thearch.Gins(Thearch.Optoas(OCMP, nr.Type), l, r)

	// Handle floating point special cases.
	// Note that 8g has Bgen_float and is handled above.
	if Isfloat[nl.Type.Etype] {
		switch Ctxt.Arch.Thechar {
		case '5':
			if genval {
				Fatal("genval 5g Isfloat special cases not implemented")
			}
			switch n.Op {
			case ONE:
				Patch(Gbranch(Thearch.Optoas(OPS, nr.Type), nr.Type, likely), to)
				Patch(Gbranch(Thearch.Optoas(a, nr.Type), nr.Type, likely), to)
			default:
				p := Gbranch(Thearch.Optoas(OPS, nr.Type), nr.Type, -likely)
				Patch(Gbranch(Thearch.Optoas(a, nr.Type), nr.Type, likely), to)
				Patch(p, Pc)
			}
			return
		case '6':
			switch n.Op {
			case OEQ:
				// neither NE nor P
				if genval {
					var reg Node
					Regalloc(&reg, Types[TBOOL], nil)
					Thearch.Ginsboolval(Thearch.Optoas(OEQ, nr.Type), &reg)
					Thearch.Ginsboolval(Thearch.Optoas(OPC, nr.Type), res)
					Thearch.Gins(Thearch.Optoas(OAND, Types[TBOOL]), &reg, res)
					Regfree(&reg)
				} else {
					p1 := Gbranch(Thearch.Optoas(ONE, nr.Type), nil, -likely)
					p2 := Gbranch(Thearch.Optoas(OPS, nr.Type), nil, -likely)
					Patch(Gbranch(obj.AJMP, nil, 0), to)
					Patch(p1, Pc)
					Patch(p2, Pc)
				}
				return
			case ONE:
				// either NE or P
				if genval {
					var reg Node
					Regalloc(&reg, Types[TBOOL], nil)
					Thearch.Ginsboolval(Thearch.Optoas(ONE, nr.Type), &reg)
					Thearch.Ginsboolval(Thearch.Optoas(OPS, nr.Type), res)
					Thearch.Gins(Thearch.Optoas(OOR, Types[TBOOL]), &reg, res)
					Regfree(&reg)
				} else {
					Patch(Gbranch(Thearch.Optoas(ONE, nr.Type), nil, likely), to)
					Patch(Gbranch(Thearch.Optoas(OPS, nr.Type), nil, likely), to)
				}
				return
			}
		case '7', '9':
			if genval {
				Fatal("genval 7g, 9g Isfloat special cases not implemented")
			}
			switch n.Op {
			// On arm64 and ppc64, <= and >= mishandle NaN. Must decompose into < or > and =.
			// TODO(josh): Convert a <= b to b > a instead?
			case OLE, OGE:
				if a == OLE {
					a = OLT
				} else {
					a = OGT
				}
				Patch(Gbranch(Thearch.Optoas(a, nr.Type), nr.Type, likely), to)
				Patch(Gbranch(Thearch.Optoas(OEQ, nr.Type), nr.Type, likely), to)
				return
			}
		}
	}

	// Not a special case. Insert the conditional jump or value gen.
	bins(nr.Type, res, a, likely, to)
}

func bgenNonZero(n, res *Node, wantTrue bool, likely int, to *obj.Prog) {
	// TODO: Optimize on systems that can compare to zero easily.
	a := ONE
	if !wantTrue {
		a = OEQ
	}
	var zero Node
	Nodconst(&zero, n.Type, 0)
	Thearch.Gins(Thearch.Optoas(OCMP, n.Type), n, &zero)
	bins(n.Type, res, a, likely, to)
}

// bins inserts an instruction to handle the result of a compare.
// If res is non-nil, it inserts appropriate value generation instructions.
// If res is nil, it inserts a branch to to.
func bins(typ *Type, res *Node, a, likely int, to *obj.Prog) {
	a = Thearch.Optoas(a, typ)
	if res != nil {
		// value gen
		Thearch.Ginsboolval(a, res)
	} else {
		// jump
		Patch(Gbranch(a, typ, likely), to)
	}
}

/*
 * n is on stack, either local variable
 * or return value from function call.
 * return n's offset from SP.
 */
func stkof(n *Node) int64 {
	switch n.Op {
	case OINDREG:
		return n.Xoffset

	case ODOT:
		t := n.Left.Type
		if Isptr[t.Etype] {
			break
		}
		off := stkof(n.Left)
		if off == -1000 || off == 1000 {
			return off
		}
		return off + n.Xoffset

	case OINDEX:
		t := n.Left.Type
		if !Isfixedarray(t) {
			break
		}
		off := stkof(n.Left)
		if off == -1000 || off == 1000 {
			return off
		}
		if Isconst(n.Right, CTINT) {
			return off + t.Type.Width*Mpgetfix(n.Right.Val.U.Xval)
		}
		return 1000

	case OCALLMETH, OCALLINTER, OCALLFUNC:
		t := n.Left.Type
		if Isptr[t.Etype] {
			t = t.Type
		}

		var flist Iter
		t = Structfirst(&flist, Getoutarg(t))
		if t != nil {
			w := t.Width
			if HasLinkRegister() {
				w += int64(Ctxt.Arch.Ptrsize)
			}
			return w
		}
	}

	// botch - probably failing to recognize address
	// arithmetic on the above. eg INDEX and DOT
	return -1000
}

/*
 * block copy:
 *	memmove(&ns, &n, w);
 * if wb is true, needs write barrier.
 */
func sgen_wb(n *Node, ns *Node, w int64, wb bool) {
	if Debug['g'] != 0 {
		op := "sgen"
		if wb {
			op = "sgen-wb"
		}
		fmt.Printf("\n%s w=%d\n", op, w)
		Dump("r", n)
		Dump("res", ns)
	}

	if n.Ullman >= UINF && ns.Ullman >= UINF {
		Fatal("sgen UINF")
	}

	if w < 0 {
		Fatal("sgen copy %d", w)
	}

	// If copying .args, that's all the results, so record definition sites
	// for them for the liveness analysis.
	if ns.Op == ONAME && ns.Sym.Name == ".args" {
		for l := Curfn.Func.Dcl; l != nil; l = l.Next {
			if l.N.Class == PPARAMOUT {
				Gvardef(l.N)
			}
		}
	}

	// Avoid taking the address for simple enough types.
	if componentgen_wb(n, ns, wb) {
		return
	}

	if w == 0 {
		// evaluate side effects only
		var nodr Node
		Regalloc(&nodr, Types[Tptr], nil)
		Agen(ns, &nodr)
		Agen(n, &nodr)
		Regfree(&nodr)
		return
	}

	// offset on the stack
	osrc := stkof(n)
	odst := stkof(ns)

	if odst != -1000 {
		// on stack, write barrier not needed after all
		wb = false
	}

	if osrc != -1000 && odst != -1000 && (osrc == 1000 || odst == 1000) || wb && osrc != -1000 {
		// osrc and odst both on stack, and at least one is in
		// an unknown position.  Could generate code to test
		// for forward/backward copy, but instead just copy
		// to a temporary location first.
		//
		// OR: write barrier needed and source is on stack.
		// Invoking the write barrier will use the stack to prepare its call.
		// Copy to temporary.
		var tmp Node
		Tempname(&tmp, n.Type)
		sgen_wb(n, &tmp, w, false)
		sgen_wb(&tmp, ns, w, wb)
		return
	}

	if wb {
		cgen_wbfat(n, ns)
		return
	}

	Thearch.Blockcopy(n, ns, osrc, odst, w)
}

/*
 * generate:
 *	call f
 *	proc=-1	normal call but no return
 *	proc=0	normal call
 *	proc=1	goroutine run in new proc
 *	proc=2	defer call save away stack
  *	proc=3	normal call to C pointer (not Go func value)
*/
func Ginscall(f *Node, proc int) {
	if f.Type != nil {
		extra := int32(0)
		if proc == 1 || proc == 2 {
			extra = 2 * int32(Widthptr)
		}
		Setmaxarg(f.Type, extra)
	}

	switch proc {
	default:
		Fatal("Ginscall: bad proc %d", proc)

	case 0, // normal call
		-1: // normal call but no return
		if f.Op == ONAME && f.Class == PFUNC {
			if f == Deferreturn {
				// Deferred calls will appear to be returning to
				// the CALL deferreturn(SB) that we are about to emit.
				// However, the stack trace code will show the line
				// of the instruction byte before the return PC.
				// To avoid that being an unrelated instruction,
				// insert an actual hardware NOP that will have the right line number.
				// This is different from obj.ANOP, which is a virtual no-op
				// that doesn't make it into the instruction stream.
				Thearch.Ginsnop()
			}

			p := Thearch.Gins(obj.ACALL, nil, f)
			Afunclit(&p.To, f)
			if proc == -1 || Noreturn(p) {
				Thearch.Gins(obj.AUNDEF, nil, nil)
			}
			break
		}

		var reg Node
		Nodreg(&reg, Types[Tptr], Thearch.REGCTXT)
		var r1 Node
		Nodreg(&r1, Types[Tptr], Thearch.REGCALLX)
		Thearch.Gmove(f, &reg)
		reg.Op = OINDREG
		Thearch.Gmove(&reg, &r1)
		reg.Op = OREGISTER
		Thearch.Gins(obj.ACALL, &reg, &r1)

	case 3: // normal call of c function pointer
		Thearch.Gins(obj.ACALL, nil, f)

	case 1, // call in new proc (go)
		2: // deferred call (defer)
		var stk Node

		// size of arguments at 0(SP)
		stk.Op = OINDREG
		stk.Reg = int16(Thearch.REGSP)
		stk.Xoffset = 0
		if HasLinkRegister() {
			stk.Xoffset += int64(Ctxt.Arch.Ptrsize)
		}
		Thearch.Ginscon(Thearch.Optoas(OAS, Types[TINT32]), int64(Argsize(f.Type)), &stk)

		// FuncVal* at 8(SP)
		stk.Xoffset = int64(Widthptr)
		if HasLinkRegister() {
			stk.Xoffset += int64(Ctxt.Arch.Ptrsize)
		}

		var reg Node
		Nodreg(&reg, Types[Tptr], Thearch.REGCALLX2)
		Thearch.Gmove(f, &reg)
		Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &reg, &stk)

		if proc == 1 {
			Ginscall(Newproc, 0)
		} else {
			if Hasdefer == 0 {
				Fatal("hasdefer=0 but has defer")
			}
			Ginscall(Deferproc, 0)
		}

		if proc == 2 {
			Nodreg(&reg, Types[TINT32], Thearch.REGRETURN)
			p := Thearch.Ginscmp(OEQ, Types[TINT32], &reg, Nodintconst(0), +1)
			cgen_ret(nil)
			Patch(p, Pc)
		}
	}
}

/*
 * n is call to interface method.
 * generate res = n.
 */
func cgen_callinter(n *Node, res *Node, proc int) {
	i := n.Left
	if i.Op != ODOTINTER {
		Fatal("cgen_callinter: not ODOTINTER %v", Oconv(int(i.Op), 0))
	}

	f := i.Right // field
	if f.Op != ONAME {
		Fatal("cgen_callinter: not ONAME %v", Oconv(int(f.Op), 0))
	}

	i = i.Left // interface

	if !i.Addable {
		var tmpi Node
		Tempname(&tmpi, i.Type)
		Cgen(i, &tmpi)
		i = &tmpi
	}

	Genlist(n.List) // assign the args

	// i is now addable, prepare an indirected
	// register to hold its address.
	var nodi Node
	Igen(i, &nodi, res) // REG = &inter

	var nodsp Node
	Nodindreg(&nodsp, Types[Tptr], Thearch.REGSP)
	nodsp.Xoffset = 0
	if HasLinkRegister() {
		nodsp.Xoffset += int64(Ctxt.Arch.Ptrsize)
	}
	if proc != 0 {
		nodsp.Xoffset += 2 * int64(Widthptr) // leave room for size & fn
	}
	nodi.Type = Types[Tptr]
	nodi.Xoffset += int64(Widthptr)
	Cgen(&nodi, &nodsp) // {0, 8(nacl), or 16}(SP) = 8(REG) -- i.data

	var nodo Node
	Regalloc(&nodo, Types[Tptr], res)

	nodi.Type = Types[Tptr]
	nodi.Xoffset -= int64(Widthptr)
	Cgen(&nodi, &nodo) // REG = 0(REG) -- i.tab
	Regfree(&nodi)

	var nodr Node
	Regalloc(&nodr, Types[Tptr], &nodo)
	if n.Left.Xoffset == BADWIDTH {
		Fatal("cgen_callinter: badwidth")
	}
	Cgen_checknil(&nodo) // in case offset is huge
	nodo.Op = OINDREG
	nodo.Xoffset = n.Left.Xoffset + 3*int64(Widthptr) + 8
	if proc == 0 {
		// plain call: use direct c function pointer - more efficient
		Cgen(&nodo, &nodr) // REG = 32+offset(REG) -- i.tab->fun[f]
		proc = 3
	} else {
		// go/defer. generate go func value.
		Agen(&nodo, &nodr) // REG = &(32+offset(REG)) -- i.tab->fun[f]
	}

	nodr.Type = n.Left.Type
	Ginscall(&nodr, proc)

	Regfree(&nodr)
	Regfree(&nodo)
}

/*
 * generate function call;
 *	proc=0	normal call
 *	proc=1	goroutine run in new proc
 *	proc=2	defer call save away stack
 */
func cgen_call(n *Node, proc int) {
	if n == nil {
		return
	}

	var afun Node
	if n.Left.Ullman >= UINF {
		// if name involves a fn call
		// precompute the address of the fn
		Tempname(&afun, Types[Tptr])

		Cgen(n.Left, &afun)
	}

	Genlist(n.List) // assign the args
	t := n.Left.Type

	// call tempname pointer
	if n.Left.Ullman >= UINF {
		var nod Node
		Regalloc(&nod, Types[Tptr], nil)
		Cgen_as(&nod, &afun)
		nod.Type = t
		Ginscall(&nod, proc)
		Regfree(&nod)
		return
	}

	// call pointer
	if n.Left.Op != ONAME || n.Left.Class != PFUNC {
		var nod Node
		Regalloc(&nod, Types[Tptr], nil)
		Cgen_as(&nod, n.Left)
		nod.Type = t
		Ginscall(&nod, proc)
		Regfree(&nod)
		return
	}

	// call direct
	n.Left.Method = true

	Ginscall(n.Left, proc)
}

func HasLinkRegister() bool {
	c := Ctxt.Arch.Thechar
	return c != '6' && c != '8'
}

/*
 * call to n has already been generated.
 * generate:
 *	res = return value from call.
 */
func cgen_callret(n *Node, res *Node) {
	t := n.Left.Type
	if t.Etype == TPTR32 || t.Etype == TPTR64 {
		t = t.Type
	}

	var flist Iter
	fp := Structfirst(&flist, Getoutarg(t))
	if fp == nil {
		Fatal("cgen_callret: nil")
	}

	var nod Node
	nod.Op = OINDREG
	nod.Reg = int16(Thearch.REGSP)
	nod.Addable = true

	nod.Xoffset = fp.Width
	if HasLinkRegister() {
		nod.Xoffset += int64(Ctxt.Arch.Ptrsize)
	}
	nod.Type = fp.Type
	Cgen_as(res, &nod)
}

/*
 * call to n has already been generated.
 * generate:
 *	res = &return value from call.
 */
func cgen_aret(n *Node, res *Node) {
	t := n.Left.Type
	if Isptr[t.Etype] {
		t = t.Type
	}

	var flist Iter
	fp := Structfirst(&flist, Getoutarg(t))
	if fp == nil {
		Fatal("cgen_aret: nil")
	}

	var nod1 Node
	nod1.Op = OINDREG
	nod1.Reg = int16(Thearch.REGSP)
	nod1.Addable = true
	nod1.Xoffset = fp.Width
	if HasLinkRegister() {
		nod1.Xoffset += int64(Ctxt.Arch.Ptrsize)
	}
	nod1.Type = fp.Type

	if res.Op != OREGISTER {
		var nod2 Node
		Regalloc(&nod2, Types[Tptr], res)
		Agen(&nod1, &nod2)
		Thearch.Gins(Thearch.Optoas(OAS, Types[Tptr]), &nod2, res)
		Regfree(&nod2)
	} else {
		Agen(&nod1, res)
	}
}

/*
 * generate return.
 * n->left is assignments to return values.
 */
func cgen_ret(n *Node) {
	if n != nil {
		Genlist(n.List) // copy out args
	}
	if Hasdefer != 0 {
		Ginscall(Deferreturn, 0)
	}
	Genlist(Curfn.Func.Exit)
	p := Thearch.Gins(obj.ARET, nil, nil)
	if n != nil && n.Op == ORETJMP {
		p.To.Type = obj.TYPE_MEM
		p.To.Name = obj.NAME_EXTERN
		p.To.Sym = Linksym(n.Left.Sym)
	}
}

/*
 * generate division according to op, one of:
 *	res = nl / nr
 *	res = nl % nr
 */
func cgen_div(op int, nl *Node, nr *Node, res *Node) {
	var w int

	// TODO(rsc): arm64 needs to support the relevant instructions
	// in peep and optoas in order to enable this.
	// TODO(rsc): ppc64 needs to support the relevant instructions
	// in peep and optoas in order to enable this.
	if nr.Op != OLITERAL || Ctxt.Arch.Thechar == '7' || Ctxt.Arch.Thechar == '9' {
		goto longdiv
	}
	w = int(nl.Type.Width * 8)

	// Front end handled 32-bit division. We only need to handle 64-bit.
	// try to do division by multiply by (2^w)/d
	// see hacker's delight chapter 10
	switch Simtype[nl.Type.Etype] {
	default:
		goto longdiv

	case TUINT64:
		var m Magic
		m.W = w
		m.Ud = uint64(Mpgetfix(nr.Val.U.Xval))
		Umagic(&m)
		if m.Bad != 0 {
			break
		}
		if op == OMOD {
			goto longmod
		}

		var n1 Node
		Cgenr(nl, &n1, nil)
		var n2 Node
		Nodconst(&n2, nl.Type, int64(m.Um))
		var n3 Node
		Regalloc(&n3, nl.Type, res)
		Thearch.Cgen_hmul(&n1, &n2, &n3)

		if m.Ua != 0 {
			// need to add numerator accounting for overflow
			Thearch.Gins(Thearch.Optoas(OADD, nl.Type), &n1, &n3)

			Nodconst(&n2, nl.Type, 1)
			Thearch.Gins(Thearch.Optoas(ORROTC, nl.Type), &n2, &n3)
			Nodconst(&n2, nl.Type, int64(m.S)-1)
			Thearch.Gins(Thearch.Optoas(ORSH, nl.Type), &n2, &n3)
		} else {
			Nodconst(&n2, nl.Type, int64(m.S))
			Thearch.Gins(Thearch.Optoas(ORSH, nl.Type), &n2, &n3) // shift dx
		}

		Thearch.Gmove(&n3, res)
		Regfree(&n1)
		Regfree(&n3)
		return

	case TINT64:
		var m Magic
		m.W = w
		m.Sd = Mpgetfix(nr.Val.U.Xval)
		Smagic(&m)
		if m.Bad != 0 {
			break
		}
		if op == OMOD {
			goto longmod
		}

		var n1 Node
		Cgenr(nl, &n1, res)
		var n2 Node
		Nodconst(&n2, nl.Type, m.Sm)
		var n3 Node
		Regalloc(&n3, nl.Type, nil)
		Thearch.Cgen_hmul(&n1, &n2, &n3)

		if m.Sm < 0 {
			// need to add numerator
			Thearch.Gins(Thearch.Optoas(OADD, nl.Type), &n1, &n3)
		}

		Nodconst(&n2, nl.Type, int64(m.S))
		Thearch.Gins(Thearch.Optoas(ORSH, nl.Type), &n2, &n3) // shift n3

		Nodconst(&n2, nl.Type, int64(w)-1)

		Thearch.Gins(Thearch.Optoas(ORSH, nl.Type), &n2, &n1) // -1 iff num is neg
		Thearch.Gins(Thearch.Optoas(OSUB, nl.Type), &n1, &n3) // added

		if m.Sd < 0 {
			// this could probably be removed
			// by factoring it into the multiplier
			Thearch.Gins(Thearch.Optoas(OMINUS, nl.Type), nil, &n3)
		}

		Thearch.Gmove(&n3, res)
		Regfree(&n1)
		Regfree(&n3)
		return
	}

	goto longdiv

	// division and mod using (slow) hardware instruction
longdiv:
	Thearch.Dodiv(op, nl, nr, res)

	return

	// mod using formula A%B = A-(A/B*B) but
	// we know that there is a fast algorithm for A/B
longmod:
	var n1 Node
	Regalloc(&n1, nl.Type, res)

	Cgen(nl, &n1)
	var n2 Node
	Regalloc(&n2, nl.Type, nil)
	cgen_div(ODIV, &n1, nr, &n2)
	a := Thearch.Optoas(OMUL, nl.Type)
	if w == 8 {
		// use 2-operand 16-bit multiply
		// because there is no 2-operand 8-bit multiply
		a = Thearch.Optoas(OMUL, Types[TINT16]) // XXX was IMULW
	}

	if !Smallintconst(nr) {
		var n3 Node
		Regalloc(&n3, nl.Type, nil)
		Cgen(nr, &n3)
		Thearch.Gins(a, &n3, &n2)
		Regfree(&n3)
	} else {
		Thearch.Gins(a, nr, &n2)
	}
	Thearch.Gins(Thearch.Optoas(OSUB, nl.Type), &n2, &n1)
	Thearch.Gmove(&n1, res)
	Regfree(&n1)
	Regfree(&n2)
}

func Fixlargeoffset(n *Node) {
	if n == nil {
		return
	}
	if n.Op != OINDREG {
		return
	}
	if n.Reg == int16(Thearch.REGSP) { // stack offset cannot be large
		return
	}
	if n.Xoffset != int64(int32(n.Xoffset)) {
		// offset too large, add to register instead.
		a := *n

		a.Op = OREGISTER
		a.Type = Types[Tptr]
		a.Xoffset = 0
		Cgen_checknil(&a)
		Thearch.Ginscon(Thearch.Optoas(OADD, Types[Tptr]), n.Xoffset, &a)
		n.Xoffset = 0
	}
}

func cgen_append(n, res *Node) {
	if Debug['g'] != 0 {
		Dump("cgen_append-n", n)
		Dump("cgen_append-res", res)
	}
	if res.Op != ONAME && !samesafeexpr(res, n.List.N) {
		Dump("cgen_append-n", n)
		Dump("cgen_append-res", res)
		Fatal("append not lowered")
	}
	for l := n.List; l != nil; l = l.Next {
		if l.N.Ullman >= UINF {
			Fatal("append with function call arguments")
		}
	}

	// res = append(src, x, y, z)
	//
	// If res and src are the same, we can avoid writing to base and cap
	// unless we grow the underlying array.
	needFullUpdate := !samesafeexpr(res, n.List.N)

	// Copy src triple into base, len, cap.
	base := temp(Types[Tptr])
	len := temp(Types[TUINT])
	cap := temp(Types[TUINT])

	var src Node
	Igen(n.List.N, &src, nil)
	src.Type = Types[Tptr]
	Thearch.Gmove(&src, base)
	src.Type = Types[TUINT]
	src.Xoffset += int64(Widthptr)
	Thearch.Gmove(&src, len)
	src.Xoffset += int64(Widthptr)
	Thearch.Gmove(&src, cap)

	// if len+argc <= cap goto L1
	var rlen Node
	Regalloc(&rlen, Types[TUINT], nil)
	Thearch.Gmove(len, &rlen)
	Thearch.Ginscon(Thearch.Optoas(OADD, Types[TUINT]), int64(count(n.List)-1), &rlen)
	p := Thearch.Ginscmp(OLE, Types[TUINT], &rlen, cap, +1)
	// Note: rlen and src are Regrealloc'ed below at the target of the
	// branch we just emitted; do not reuse these Go variables for
	// other purposes. They need to still describe the same things
	// below that they describe right here.
	Regfree(&src)

	// base, len, cap = growslice(type, base, len, cap, newlen)
	var arg Node
	arg.Op = OINDREG
	arg.Reg = int16(Thearch.REGSP)
	arg.Addable = true
	arg.Xoffset = 0
	if HasLinkRegister() {
		arg.Xoffset = int64(Ctxt.Arch.Ptrsize)
	}
	arg.Type = Ptrto(Types[TUINT8])
	Cgen(typename(res.Type), &arg)
	arg.Xoffset += int64(Widthptr)

	arg.Type = Types[Tptr]
	Cgen(base, &arg)
	arg.Xoffset += int64(Widthptr)

	arg.Type = Types[TUINT]
	Cgen(len, &arg)
	arg.Xoffset += int64(Widthptr)

	arg.Type = Types[TUINT]
	Cgen(cap, &arg)
	arg.Xoffset += int64(Widthptr)

	arg.Type = Types[TUINT]
	Cgen(&rlen, &arg)
	arg.Xoffset += int64(Widthptr)
	Regfree(&rlen)

	fn := syslook("growslice", 1)
	substArgTypes(fn, res.Type.Type, res.Type.Type)
	Ginscall(fn, 0)

	if Widthptr == 4 && Widthreg == 8 {
		arg.Xoffset += 4
	}

	arg.Type = Types[Tptr]
	Cgen(&arg, base)
	arg.Xoffset += int64(Widthptr)

	arg.Type = Types[TUINT]
	Cgen(&arg, len)
	arg.Xoffset += int64(Widthptr)

	arg.Type = Types[TUINT]
	Cgen(&arg, cap)

	// Update res with base, len+argc, cap.
	if needFullUpdate {
		if Debug_append > 0 {
			Warn("append: full update")
		}
		Patch(p, Pc)
	}
	if res.Op == ONAME {
		Gvardef(res)
	}
	var dst, r1 Node
	Igen(res, &dst, nil)
	dst.Type = Types[TUINT]
	dst.Xoffset += int64(Widthptr)
	Regalloc(&r1, Types[TUINT], nil)
	Thearch.Gmove(len, &r1)
	Thearch.Ginscon(Thearch.Optoas(OADD, Types[TUINT]), int64(count(n.List)-1), &r1)
	Thearch.Gmove(&r1, &dst)
	Regfree(&r1)
	dst.Xoffset += int64(Widthptr)
	Thearch.Gmove(cap, &dst)
	dst.Type = Types[Tptr]
	dst.Xoffset -= 2 * int64(Widthptr)
	cgen_wb(base, &dst, needwritebarrier(&dst, base))
	Regfree(&dst)

	if !needFullUpdate {
		if Debug_append > 0 {
			Warn("append: len-only update")
		}
		// goto L2;
		// L1:
		//	update len only
		// L2:
		q := Gbranch(obj.AJMP, nil, 0)
		Patch(p, Pc)
		// At the goto above, src refers to cap and rlen holds the new len
		if src.Op == OREGISTER || src.Op == OINDREG {
			Regrealloc(&src)
		}
		Regrealloc(&rlen)
		src.Xoffset -= int64(Widthptr)
		Thearch.Gmove(&rlen, &src)
		Regfree(&src)
		Regfree(&rlen)
		Patch(q, Pc)
	}

	// Copy data into place.
	// Could do write barrier check around entire copy instead of each element.
	// Could avoid reloading registers on each iteration if we know the cgen_wb
	// is not going to use a write barrier.
	i := 0
	var r2 Node
	for l := n.List.Next; l != nil; l = l.Next {
		Regalloc(&r1, Types[Tptr], nil)
		Thearch.Gmove(base, &r1)
		Regalloc(&r2, Types[TUINT], nil)
		Thearch.Gmove(len, &r2)
		if i > 0 {
			Thearch.Gins(Thearch.Optoas(OADD, Types[TUINT]), Nodintconst(int64(i)), &r2)
		}
		w := res.Type.Type.Width
		if Thearch.AddIndex != nil && Thearch.AddIndex(&r2, w, &r1) {
			// r1 updated by back end
		} else if w == 1 {
			Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &r2, &r1)
		} else {
			Thearch.Ginscon(Thearch.Optoas(OMUL, Types[TUINT]), int64(w), &r2)
			Thearch.Gins(Thearch.Optoas(OADD, Types[Tptr]), &r2, &r1)
		}
		Regfree(&r2)

		r1.Op = OINDREG
		r1.Type = res.Type.Type
		cgen_wb(l.N, &r1, needwritebarrier(&r1, l.N))
		Regfree(&r1)
		i++
	}
}

// Generate res = n, where n is x[i:j] or x[i:j:k].
// If wb is true, need write barrier updating res's base pointer.
// On systems with 32-bit ints, i, j, k are guaranteed to be 32-bit values.
func cgen_slice(n, res *Node, wb bool) {
	needFullUpdate := !samesafeexpr(n.Left, res)

	// orderexpr has made sure that x is safe (but possibly expensive)
	// and i, j, k are cheap. On a system with registers (anything but 386)
	// we can evaluate x first and then know we have enough registers
	// for i, j, k as well.
	var x, xbase, xlen, xcap, i, j, k Node
	if n.Op != OSLICEARR && n.Op != OSLICE3ARR {
		Igen(n.Left, &x, nil)
	}

	indexRegType := Types[TUINT]
	if Widthreg > Widthptr { // amd64p32
		indexRegType = Types[TUINT64]
	}

	// On most systems, we use registers.
	// The 386 has basically no registers, so substitute functions
	// that can work with temporaries instead.
	regalloc := Regalloc
	ginscon := Thearch.Ginscon
	gins := Thearch.Gins
	if Thearch.Thechar == '8' {
		regalloc = func(n *Node, t *Type, reuse *Node) {
			Tempname(n, t)
		}
		ginscon = func(as int, c int64, n *Node) {
			var n1 Node
			Regalloc(&n1, n.Type, n)
			Thearch.Gmove(n, &n1)
			Thearch.Ginscon(as, c, &n1)
			Thearch.Gmove(&n1, n)
			Regfree(&n1)
		}
		gins = func(as int, f, t *Node) *obj.Prog {
			var n1 Node
			Regalloc(&n1, t.Type, t)
			Thearch.Gmove(t, &n1)
			Thearch.Gins(as, f, &n1)
			Thearch.Gmove(&n1, t)
			Regfree(&n1)
			return nil
		}
	}

	panics := make([]*obj.Prog, 0, 6) // 3 loads + 3 checks

	loadlen := func() {
		if xlen.Op != 0 {
			return
		}
		if n.Op == OSLICEARR || n.Op == OSLICE3ARR {
			Nodconst(&xlen, indexRegType, n.Left.Type.Type.Bound)
			return
		}
		if n.Op == OSLICESTR && Isconst(n.Left, CTSTR) {
			Nodconst(&xlen, indexRegType, int64(len(n.Left.Val.U.Sval)))
			return
		}
		regalloc(&xlen, indexRegType, nil)
		x.Xoffset += int64(Widthptr)
		x.Type = Types[TUINT]
		Thearch.Gmove(&x, &xlen)
		x.Xoffset -= int64(Widthptr)
	}

	loadcap := func() {
		if xcap.Op != 0 {
			return
		}
		if n.Op == OSLICEARR || n.Op == OSLICE3ARR || n.Op == OSLICESTR {
			loadlen()
			xcap = xlen
			if xcap.Op == OREGISTER {
				Regrealloc(&xcap)
			}
			return
		}
		regalloc(&xcap, indexRegType, nil)
		x.Xoffset += 2 * int64(Widthptr)
		x.Type = Types[TUINT]
		Thearch.Gmove(&x, &xcap)
		x.Xoffset -= 2 * int64(Widthptr)
	}

	var x1, x2, x3 *Node // unevaluated index arguments
	x1 = n.Right.Left
	switch n.Op {
	default:
		x2 = n.Right.Right
	case OSLICE3, OSLICE3ARR:
		x2 = n.Right.Right.Left
		x3 = n.Right.Right.Right
	}

	// load computes src into targ, but if src refers to the len or cap of n.Left,
	// load copies those from xlen, xcap, loading xlen if needed.
	// If targ.Op == OREGISTER on return, it must be Regfreed,
	// but it should not be modified without first checking whether it is
	// xlen or xcap's register.
	load := func(src, targ *Node) {
		if src == nil {
			return
		}
		switch src.Op {
		case OLITERAL:
			*targ = *src
			return
		case OLEN:
			// NOTE(rsc): This doesn't actually trigger, because order.go
			// has pulled all the len and cap calls into separate assignments
			// to temporaries. There are tests in test/sliceopt.go that could
			// be enabled if this is fixed.
			if samesafeexpr(n.Left, src.Left) {
				if Debug_slice > 0 {
					Warn("slice: reuse len")
				}
				loadlen()
				*targ = xlen
				if targ.Op == OREGISTER {
					Regrealloc(targ)
				}
				return
			}
		case OCAP:
			// NOTE(rsc): This doesn't actually trigger; see note in case OLEN above.
			if samesafeexpr(n.Left, src.Left) {
				if Debug_slice > 0 {
					Warn("slice: reuse cap")
				}
				loadcap()
				*targ = xcap
				if targ.Op == OREGISTER {
					Regrealloc(targ)
				}
				return
			}
		}
		if i.Op != 0 && samesafeexpr(x1, src) {
			if Debug_slice > 0 {
				Warn("slice: reuse 1st index")
			}
			*targ = i
			if targ.Op == OREGISTER {
				Regrealloc(targ)
			}
			return
		}
		if j.Op != 0 && samesafeexpr(x2, src) {
			if Debug_slice > 0 {
				Warn("slice: reuse 2nd index")
			}
			*targ = j
			if targ.Op == OREGISTER {
				Regrealloc(targ)
			}
			return
		}
		if Thearch.Cgenindex != nil {
			regalloc(targ, indexRegType, nil)
			p := Thearch.Cgenindex(src, targ, false)
			if p != nil {
				panics = append(panics, p)
			}
		} else if Thearch.Igenindex != nil {
			p := Thearch.Igenindex(src, targ, false)
			if p != nil {
				panics = append(panics, p)
			}
		} else {
			regalloc(targ, indexRegType, nil)
			var tmp Node
			Cgenr(src, &tmp, targ)
			Thearch.Gmove(&tmp, targ)
			Regfree(&tmp)
		}
	}

	load(x1, &i)
	load(x2, &j)
	load(x3, &k)

	// i defaults to 0.
	if i.Op == 0 {
		Nodconst(&i, indexRegType, 0)
	}

	// j defaults to len(x)
	if j.Op == 0 {
		loadlen()
		j = xlen
		if j.Op == OREGISTER {
			Regrealloc(&j)
		}
	}

	// k defaults to cap(x)
	// Only need to load it if we're recalculating cap or doing a full update.
	if k.Op == 0 && n.Op != OSLICESTR && (!iszero(&i) || needFullUpdate) {
		loadcap()
		k = xcap
		if k.Op == OREGISTER {
			Regrealloc(&k)
		}
	}

	// Check constant indexes for negative values, and against constant length if known.
	// The func obvious below checks for out-of-order constant indexes.
	var bound int64 = -1
	if n.Op == OSLICEARR || n.Op == OSLICE3ARR {
		bound = n.Left.Type.Type.Bound
	} else if n.Op == OSLICESTR && Isconst(n.Left, CTSTR) {
		bound = int64(len(n.Left.Val.U.Sval))
	}
	if Isconst(&i, CTINT) {
		if mpcmpfixc(i.Val.U.Xval, 0) < 0 || bound >= 0 && mpcmpfixc(i.Val.U.Xval, bound) > 0 {
			Yyerror("slice index out of bounds")
		}
	}
	if Isconst(&j, CTINT) {
		if mpcmpfixc(j.Val.U.Xval, 0) < 0 || bound >= 0 && mpcmpfixc(j.Val.U.Xval, bound) > 0 {
			Yyerror("slice index out of bounds")
		}
	}
	if Isconst(&k, CTINT) {
		if mpcmpfixc(k.Val.U.Xval, 0) < 0 || bound >= 0 && mpcmpfixc(k.Val.U.Xval, bound) > 0 {
			Yyerror("slice index out of bounds")
		}
	}

	// same reports whether n1 and n2 are the same register or constant.
	same := func(n1, n2 *Node) bool {
		return n1.Op == OREGISTER && n2.Op == OREGISTER && n1.Reg == n2.Reg ||
			n1.Op == ONAME && n2.Op == ONAME && n1.Orig == n2.Orig && n1.Type == n2.Type && n1.Xoffset == n2.Xoffset ||
			n1.Op == OLITERAL && n2.Op == OLITERAL && Mpcmpfixfix(n1.Val.U.Xval, n2.Val.U.Xval) == 0
	}

	// obvious reports whether n1 <= n2 is obviously true,
	// and it calls Yyerror if n1 <= n2 is obviously false.
	obvious := func(n1, n2 *Node) bool {
		if Debug['B'] != 0 { // -B disables bounds checks
			return true
		}
		if same(n1, n2) {
			return true // n1 == n2
		}
		if iszero(n1) {
			return true // using unsigned compare, so 0 <= n2 always true
		}
		if xlen.Op != 0 && same(n1, &xlen) && xcap.Op != 0 && same(n2, &xcap) {
			return true // len(x) <= cap(x) always true
		}
		if Isconst(n1, CTINT) && Isconst(n2, CTINT) {
			if Mpcmpfixfix(n1.Val.U.Xval, n2.Val.U.Xval) <= 0 {
				return true // n1, n2 constants such that n1 <= n2
			}
			Yyerror("slice index out of bounds")
			return true
		}
		return false
	}

	compare := func(n1, n2 *Node) {
		p := Thearch.Ginscmp(OGT, indexRegType, n1, n2, -1)
		panics = append(panics, p)
	}

	loadcap()
	max := &xcap
	if k.Op != 0 && (n.Op == OSLICE3 || n.Op == OSLICE3ARR) {
		if obvious(&k, max) {
			if Debug_slice > 0 {
				Warn("slice: omit check for 3rd index")
			}
		} else {
			compare(&k, max)
		}
		max = &k
	}
	if j.Op != 0 {
		if obvious(&j, max) {
			if Debug_slice > 0 {
				Warn("slice: omit check for 2nd index")
			}
		} else {
			compare(&j, max)
		}
		max = &j
	}
	if i.Op != 0 {
		if obvious(&i, max) {
			if Debug_slice > 0 {
				Warn("slice: omit check for 1st index")
			}
		} else {
			compare(&i, max)
		}
		max = &i
	}
	if k.Op != 0 && i.Op != 0 {
		obvious(&i, &k) // emit compile-time error for x[3:n:2]
	}

	if len(panics) > 0 {
		p := Gbranch(obj.AJMP, nil, 0)
		for _, q := range panics {
			Patch(q, Pc)
		}
		Ginscall(panicslice, -1)
		Patch(p, Pc)
	}

	// Checks are done.
	// Compute new len as j-i, cap as k-i.
	// If i and j are same register, len is constant 0.
	// If i and k are same register, cap is constant 0.
	// If j and k are same register, len and cap are same.

	// Done with xlen and xcap.
	// Now safe to modify j and k even if they alias xlen, xcap.
	if xlen.Op == OREGISTER {
		Regfree(&xlen)
	}
	if xcap.Op == OREGISTER {
		Regfree(&xcap)
	}

	// are j and k the same value?
	sameJK := same(&j, &k)

	if i.Op != 0 {
		// j -= i
		if same(&i, &j) {
			if Debug_slice > 0 {
				Warn("slice: result len == 0")
			}
			if j.Op == OREGISTER {
				Regfree(&j)
			}
			Nodconst(&j, indexRegType, 0)
		} else {
			switch j.Op {
			case OLITERAL:
				if Isconst(&i, CTINT) {
					Nodconst(&j, indexRegType, Mpgetfix(j.Val.U.Xval)-Mpgetfix(i.Val.U.Xval))
					if Debug_slice > 0 {
						Warn("slice: result len == %d", Mpgetfix(j.Val.U.Xval))
					}
					break
				}
				fallthrough
			case ONAME:
				if !istemp(&j) {
					var r Node
					regalloc(&r, indexRegType, nil)
					Thearch.Gmove(&j, &r)
					j = r
				}
				fallthrough
			case OREGISTER:
				if i.Op == OLITERAL {
					v := Mpgetfix(i.Val.U.Xval)
					if v != 0 {
						ginscon(Thearch.Optoas(OSUB, indexRegType), v, &j)
					}
				} else {
					gins(Thearch.Optoas(OSUB, indexRegType), &i, &j)
				}
			}
		}

		// k -= i if k different from j and cap is needed.j
		// (The modifications to j above cannot affect i: if j and i were aliased,
		// we replace j with a constant 0 instead of doing a subtraction,
		// leaving i unmodified.)
		if k.Op == 0 {
			if Debug_slice > 0 && n.Op != OSLICESTR {
				Warn("slice: result cap not computed")
			}
			// no need
		} else if same(&i, &k) {
			if k.Op == OREGISTER {
				Regfree(&k)
			}
			Nodconst(&k, indexRegType, 0)
			if Debug_slice > 0 {
				Warn("slice: result cap == 0")
			}
		} else if sameJK {
			if Debug_slice > 0 {
				Warn("slice: result cap == result len")
			}
			// k and j were the same value; make k-i the same as j-i.
			if k.Op == OREGISTER {
				Regfree(&k)
			}
			k = j
			if k.Op == OREGISTER {
				Regrealloc(&k)
			}
		} else {
			switch k.Op {
			case OLITERAL:
				if Isconst(&i, CTINT) {
					Nodconst(&k, indexRegType, Mpgetfix(k.Val.U.Xval)-Mpgetfix(i.Val.U.Xval))
					if Debug_slice > 0 {
						Warn("slice: result cap == %d", Mpgetfix(k.Val.U.Xval))
					}
					break
				}
				fallthrough
			case ONAME:
				if !istemp(&k) {
					var r Node
					regalloc(&r, indexRegType, nil)
					Thearch.Gmove(&k, &r)
					k = r
				}
				fallthrough
			case OREGISTER:
				if same(&i, &k) {
					Regfree(&k)
					Nodconst(&k, indexRegType, 0)
					if Debug_slice > 0 {
						Warn("slice: result cap == 0")
					}
				} else if i.Op == OLITERAL {
					v := Mpgetfix(i.Val.U.Xval)
					if v != 0 {
						ginscon(Thearch.Optoas(OSUB, indexRegType), v, &k)
					}
				} else {
					gins(Thearch.Optoas(OSUB, indexRegType), &i, &k)
				}
			}
		}
	}

	adjustBase := true
	if i.Op == 0 || iszero(&i) {
		if Debug_slice > 0 {
			Warn("slice: skip base adjustment for 1st index 0")
		}
		adjustBase = false
	} else if k.Op != 0 && iszero(&k) || k.Op == 0 && iszero(&j) {
		if Debug_slice > 0 {
			if n.Op == OSLICESTR {
				Warn("slice: skip base adjustment for string len == 0")
			} else {
				Warn("slice: skip base adjustment for cap == 0")
			}
		}
		adjustBase = false
	}

	if !adjustBase && !needFullUpdate {
		if Debug_slice > 0 {
			if k.Op != 0 {
				Warn("slice: len/cap-only update")
			} else {
				Warn("slice: len-only update")
			}
		}
		if i.Op == OREGISTER {
			Regfree(&i)
		}
		// Write len (and cap if needed) back to x.
		x.Xoffset += int64(Widthptr)
		x.Type = Types[TUINT]
		Thearch.Gmove(&j, &x)
		x.Xoffset -= int64(Widthptr)
		if k.Op != 0 {
			x.Xoffset += 2 * int64(Widthptr)
			x.Type = Types[TUINT]
			Thearch.Gmove(&k, &x)
			x.Xoffset -= 2 * int64(Widthptr)
		}
		Regfree(&x)
	} else {
		// Compute new base. May smash i.
		if n.Op == OSLICEARR || n.Op == OSLICE3ARR {
			Cgenr(n.Left, &xbase, nil)
			Cgen_checknil(&xbase)
		} else {
			regalloc(&xbase, Ptrto(res.Type.Type), nil)
			x.Type = xbase.Type
			Thearch.Gmove(&x, &xbase)
			Regfree(&x)
		}
		if i.Op != 0 && adjustBase {
			// Branch around the base adjustment if the resulting cap will be 0.
			var p *obj.Prog
			size := &k
			if k.Op == 0 {
				size = &j
			}
			if Isconst(size, CTINT) {
				// zero was checked above, must be non-zero.
			} else {
				var tmp Node
				Nodconst(&tmp, indexRegType, 0)
				p = Thearch.Ginscmp(OEQ, indexRegType, size, &tmp, -1)
			}
			var w int64
			if n.Op == OSLICESTR {
				w = 1 // res is string, elem size is 1 (byte)
			} else {
				w = res.Type.Type.Width // res is []T, elem size is T.width
			}
			if Isconst(&i, CTINT) {
				ginscon(Thearch.Optoas(OADD, xbase.Type), Mpgetfix(i.Val.U.Xval)*w, &xbase)
			} else if Thearch.AddIndex != nil && Thearch.AddIndex(&i, w, &xbase) {
				// done by back end
			} else if w == 1 {
				gins(Thearch.Optoas(OADD, xbase.Type), &i, &xbase)
			} else {
				if i.Op == ONAME && !istemp(&i) {
					var tmp Node
					Tempname(&tmp, i.Type)
					Thearch.Gmove(&i, &tmp)
					i = tmp
				}
				ginscon(Thearch.Optoas(OMUL, i.Type), w, &i)
				gins(Thearch.Optoas(OADD, xbase.Type), &i, &xbase)
			}
			if p != nil {
				Patch(p, Pc)
			}
		}
		if i.Op == OREGISTER {
			Regfree(&i)
		}

		// Write len, cap, base to result.
		if res.Op == ONAME {
			Gvardef(res)
		}
		Igen(res, &x, nil)
		x.Xoffset += int64(Widthptr)
		x.Type = Types[TUINT]
		Thearch.Gmove(&j, &x)
		x.Xoffset -= int64(Widthptr)
		if k.Op != 0 {
			x.Xoffset += 2 * int64(Widthptr)
			Thearch.Gmove(&k, &x)
			x.Xoffset -= 2 * int64(Widthptr)
		}
		x.Type = xbase.Type
		cgen_wb(&xbase, &x, wb)
		Regfree(&xbase)
		Regfree(&x)
	}

	if j.Op == OREGISTER {
		Regfree(&j)
	}
	if k.Op == OREGISTER {
		Regfree(&k)
	}
}