Golang gc.Uniqp函數代碼示例

// The idea is to remove redundant copies.
//     v1->v2  F=0
//     (use v2 s/v2/v1/)*
//     set v1  F=1
//     use v2  return fail (v1->v2 move must remain)
//     -----------------
//     v1->v2  F=0
//     (use v2 s/v2/v1/)*
//     set v1  F=1
//     set v2  return success (caller can remove v1->v2 move)
func copyprop(r *gc.Flow) bool {
	p := r.Prog

	canSub := false
	switch p.As {
	case s390x.AFMOVS, s390x.AFMOVD, s390x.AMOVD:
		canSub = true
	default:
		for rr := gc.Uniqp(r); rr != nil; rr = gc.Uniqp(rr) {
			if gc.Uniqs(rr) == nil {
				break
			}
			switch copyu(rr.Prog, &p.From, nil) {
			case _Read, _None:
				continue
			}
			// write
			if rr.Prog.As == p.As {
				canSub = true
			}
			break
		}
	}
	if !canSub {
		return false
	}
	if copyas(&p.From, &p.To) {
		return true
	}

	gactive++
	return copy1(&p.From, &p.To, r.S1, 0)
}

// the idea is to substitute
// one register for another
// from one MOV to another
//	MOV	a, R1
//	ADD	b, R1	/ no use of R2
//	MOV	R1, R2
// would be converted to
//	MOV	a, R2
//	ADD	b, R2
//	MOV	R2, R1
// hopefully, then the former or latter MOV
// will be eliminated by copy propagation.
//
// r0 (the argument, not the register) is the MOV at the end of the
// above sequences. subprop returns true if it modified any instructions.
func subprop(r0 *gc.Flow) bool {
	p := r0.Prog
	v1 := &p.From
	if !isReg(v1) {
		return false
	}
	v2 := &p.To
	if !isReg(v2) {
		return false
	}
	cast := false
	switch p.As {
	case s390x.AMOVW, s390x.AMOVWZ,
		s390x.AMOVH, s390x.AMOVHZ,
		s390x.AMOVB, s390x.AMOVBZ:
		cast = true
	}
	for r := gc.Uniqp(r0); r != nil; r = gc.Uniqp(r) {
		if gc.Uniqs(r) == nil {
			break
		}
		p = r.Prog
		switch copyu(p, v1, nil) {
		case _Write, _ReadWriteDiff:
			if p.As == obj.ACALL {
				return false
			}
			if (!cast || p.As == r0.Prog.As) && p.To.Type == v1.Type && p.To.Reg == v1.Reg {
				copysub(&p.To, v1, v2)
				for r = gc.Uniqs(r); r != r0; r = gc.Uniqs(r) {
					p = r.Prog
					copysub(&p.From, v1, v2)
					copysub1(p, v1, v2)
					copysub(&p.To, v1, v2)
				}
				v1.Reg, v2.Reg = v2.Reg, v1.Reg
				return true
			}
			if cast {
				return false
			}
		case _ReadWriteSame:
			if cast {
				return false
			}
		}
		if copyu(p, v2, nil) != _None {
			return false
		}
	}
	return false
}

// is reg guaranteed to be truncated by a previous L instruction?
func prevl(r0 *gc.Flow, reg int16) bool {
	for r := gc.Uniqp(r0); r != nil; r = gc.Uniqp(r) {
		p := r.Prog
		if p.To.Type == obj.TYPE_REG && p.To.Reg == reg {
			flags := progflags(p)
			if flags&gc.RightWrite != 0 {
				if flags&gc.SizeL != 0 {
					return true
				}
				return false
			}
		}
	}
	return false
}

/*
 * findinc finds ADD instructions with a constant
 * argument which falls within the immed_12 range.
 */
func findinc(r *gc.Flow, r2 *gc.Flow, v *obj.Addr) *gc.Flow {
	var r1 *gc.Flow
	var p *obj.Prog

	for r1 = gc.Uniqs(r); r1 != nil && r1 != r2; r, r1 = r1, gc.Uniqs(r1) {
		if gc.Uniqp(r1) != r {
			return nil
		}
		switch copyu(r1.Prog, v, nil) {
		case 0: /* not touched */
			continue

		case 4: /* set and used */
			p = r1.Prog

			if p.As == arm.AADD {
				if isdconst(&p.From) {
					if p.From.Offset > -4096 && p.From.Offset < 4096 {
						return r1
					}
				}
			}
			fallthrough

		default:
			return nil
		}
	}

	return nil
}

// removeLoadHitStores trys to remove loads that take place
// immediately after a store to the same location. Returns
// true if load-hit-stores were removed.
//
// For example:
// 	MOVD	R1, 0(R15)
// 	MOVD	0(R15), R2
// Would become:
// 	MOVD	R1, 0(R15)
// 	MOVD	R1, R2
func removeLoadHitStores(r *gc.Flow) int {
	n := 0
	for ; r != nil; r = r.Link {
		p := r.Prog
		if !isStore(p) {
			continue
		}
		for rr := gc.Uniqs(r); rr != nil; rr = gc.Uniqs(rr) {
			pp := rr.Prog
			if gc.Uniqp(rr) == nil {
				break
			}
			if pp.As == obj.ANOP {
				continue
			}
			if isLoad(pp) && sameStackMem(&p.To, &pp.From) {
				if size(p.As) >= size(pp.As) && isGPR(&p.From) == isGPR(&pp.To) {
					pp.From = p.From
				}
			}
			if !isMove(pp) || isStore(pp) {
				break
			}
			if copyau(&p.From, &pp.To) {
				break
			}
		}
	}
	return n
}

/*
 * findpre returns the last instruction mentioning v
 * before r. It must be a set, and there must be
 * a unique path from that instruction to r.
 */
func findpre(r *gc.Flow, v *obj.Addr) *gc.Flow {
	var r1 *gc.Flow

	for r1 = gc.Uniqp(r); r1 != nil; r, r1 = r1, gc.Uniqp(r1) {
		if gc.Uniqs(r1) != r {
			return nil
		}
		switch copyu(r1.Prog, v, nil) {
		case 1, /* used */
			2: /* read-alter-rewrite */
			return nil

		case 3, /* set */
			4: /* set and used */
			return r1
		}
	}

	return nil
}

func conprop(r0 *gc.Flow) {
	var p *obj.Prog

	p0 := r0.Prog
	v0 := &p0.To
	r := r0

loop:
	r = gc.Uniqs(r)
	if r == nil || r == r0 {
		return
	}
	if gc.Uniqp(r) == nil {
		return
	}

	p = r.Prog
	switch copyu(p, v0, nil) {
	case 0, // miss
		1: // use
		goto loop

	case 2, // rar
		4: // use and set
		break

	case 3: // set
		if p.As == p0.As {
			if p.From.Type == p0.From.Type {
				if p.From.Reg == p0.From.Reg {
					if p.From.Node == p0.From.Node {
						if p.From.Offset == p0.From.Offset {
							if p.From.Scale == p0.From.Scale {
								if p.From.Type == obj.TYPE_FCONST && p.From.Val.(float64) == p0.From.Val.(float64) {
									if p.From.Index == p0.From.Index {
										excise(r)
										goto loop
									}
								}
							}
						}
					}
				}
			}
		}
	}
}

// copy1 replaces uses of v2 with v1 starting at r and returns true if
// all uses were rewritten.
func copy1(v1 *obj.Addr, v2 *obj.Addr, r *gc.Flow, f int) bool {
	if uint32(r.Active) == gactive {
		return true
	}
	r.Active = int32(gactive)
	for ; r != nil; r = r.S1 {
		p := r.Prog
		if f == 0 && gc.Uniqp(r) == nil {
			// Multiple predecessors; conservatively
			// assume v1 was set on other path
			f = 1
		}
		t := copyu(p, v2, nil)
		switch t {
		case _ReadWriteSame:
			return false
		case _Write:
			return true
		case _Read, _ReadWriteDiff:
			if f != 0 {
				return false
			}
			if copyu(p, v2, v1) != 0 {
				return false
			}
			if t == _ReadWriteDiff {
				return true
			}
		}
		if f == 0 {
			switch copyu(p, v1, nil) {
			case _ReadWriteSame, _ReadWriteDiff, _Write:
				f = 1
			}
		}
		if r.S2 != nil {
			if !copy1(v1, v2, r.S2, f) {
				return false
			}
		}
	}
	return true
}

/*
 * The idea is to remove redundant constants.
 *	$c1->v1
 *	($c1->v2 s/$c1/v1)*
 *	set v1  return
 * The v1->v2 should be eliminated by copy propagation.
 */
func constprop(c1 *obj.Addr, v1 *obj.Addr, r *gc.Flow) {
	if gc.Debug['P'] != 0 {
		fmt.Printf("constprop %v->%v\n", gc.Ctxt.Dconv(c1), gc.Ctxt.Dconv(v1))
	}
	var p *obj.Prog
	for ; r != nil; r = r.S1 {
		p = r.Prog
		if gc.Debug['P'] != 0 {
			fmt.Printf("%v", p)
		}
		if gc.Uniqp(r) == nil {
			if gc.Debug['P'] != 0 {
				fmt.Printf("; merge; return\n")
			}
			return
		}

		if p.As == arm.AMOVW && copyas(&p.From, c1) {
			if gc.Debug['P'] != 0 {
				fmt.Printf("; sub%v/%v", gc.Ctxt.Dconv(&p.From), gc.Ctxt.Dconv(v1))
			}
			p.From = *v1
		} else if copyu(p, v1, nil) > 1 {
			if gc.Debug['P'] != 0 {
				fmt.Printf("; %vset; return\n", gc.Ctxt.Dconv(v1))
			}
			return
		}

		if gc.Debug['P'] != 0 {
			fmt.Printf("\n")
		}
		if r.S2 != nil {
			constprop(c1, v1, r.S2)
		}
	}
}

func pushback(r0 *gc.Flow) {
	var r *gc.Flow

	var b *gc.Flow
	p0 := r0.Prog
	for r = gc.Uniqp(r0); r != nil && gc.Uniqs(r) != nil; r = gc.Uniqp(r) {
		p := r.Prog
		if p.As != obj.ANOP {
			if !(isReg(&p.From) || isConst(&p.From)) || !isReg(&p.To) {
				break
			}
			if copyu(p, &p0.To, nil) != _None || copyu(p0, &p.To, nil) != _None {
				break
			}
		}

		if p.As == obj.ACALL {
			break
		}
		b = r
	}

	if b == nil {
		if gc.Debug['P'] != 0 && gc.Debug['v'] != 0 {
			fmt.Printf("no pushback: %v\n", r0.Prog)
			if r != nil {
				fmt.Printf("\t%v [%v]\n", r.Prog, gc.Uniqs(r) != nil)
			}
		}

		return
	}

	if gc.Debug['P'] != 0 && gc.Debug['v'] != 0 {
		fmt.Printf("pushback\n")
		for r := b; ; r = r.Link {
			fmt.Printf("\t%v\n", r.Prog)
			if r == r0 {
				break
			}
		}
	}

	t := *r0.Prog
	for r = gc.Uniqp(r0); ; r = gc.Uniqp(r) {
		p0 = r.Link.Prog
		p := r.Prog
		p0.As = p.As
		p0.Lineno = p.Lineno
		p0.From = p.From
		p0.To = p.To
		p0.From3 = p.From3
		p0.Reg = p.Reg
		p0.RegTo2 = p.RegTo2
		if r == b {
			break
		}
	}

	p0 = r.Prog
	p0.As = t.As
	p0.Lineno = t.Lineno
	p0.From = t.From
	p0.To = t.To
	p0.From3 = t.From3
	p0.Reg = t.Reg
	p0.RegTo2 = t.RegTo2

	if gc.Debug['P'] != 0 && gc.Debug['v'] != 0 {
		fmt.Printf("\tafter\n")
		for r := b; ; r = r.Link {
			fmt.Printf("\t%v\n", r.Prog)
			if r == r0 {
				break
			}
		}
	}
}

/*
 * ASLL x,y,w
 * .. (not use w, not set x y w)
 * AXXX w,a,b (a != w)
 * .. (not use w)
 * (set w)
 * ----------- changed to
 * ..
 * AXXX (x<<y),a,b
 * ..
 */
func shiftprop(r *gc.Flow) bool {
	p := r.Prog
	if p.To.Type != obj.TYPE_REG {
		if gc.Debug['P'] != 0 {
			fmt.Printf("\tBOTCH: result not reg; FAILURE\n")
		}
		return false
	}

	n := p.To.Reg
	var a obj.Addr
	if p.Reg != 0 && p.Reg != p.To.Reg {
		a.Type = obj.TYPE_REG
		a.Reg = p.Reg
	}

	if gc.Debug['P'] != 0 {
		fmt.Printf("shiftprop\n%v", p)
	}
	r1 := r
	var p1 *obj.Prog
	for {
		/* find first use of shift result; abort if shift operands or result are changed */
		r1 = gc.Uniqs(r1)

		if r1 == nil {
			if gc.Debug['P'] != 0 {
				fmt.Printf("\tbranch; FAILURE\n")
			}
			return false
		}

		if gc.Uniqp(r1) == nil {
			if gc.Debug['P'] != 0 {
				fmt.Printf("\tmerge; FAILURE\n")
			}
			return false
		}

		p1 = r1.Prog
		if gc.Debug['P'] != 0 {
			fmt.Printf("\n%v", p1)
		}
		switch copyu(p1, &p.To, nil) {
		case 0: /* not used or set */
			if (p.From.Type == obj.TYPE_REG && copyu(p1, &p.From, nil) > 1) || (a.Type == obj.TYPE_REG && copyu(p1, &a, nil) > 1) {
				if gc.Debug['P'] != 0 {
					fmt.Printf("\targs modified; FAILURE\n")
				}
				return false
			}

			continue
		case 3: /* set, not used */
			{
				if gc.Debug['P'] != 0 {
					fmt.Printf("\tBOTCH: noref; FAILURE\n")
				}
				return false
			}
		}

		break
	}

	/* check whether substitution can be done */
	switch p1.As {
	default:
		if gc.Debug['P'] != 0 {
			fmt.Printf("\tnon-dpi; FAILURE\n")
		}
		return false

	case arm.AAND,
		arm.AEOR,
		arm.AADD,
		arm.AADC,
		arm.AORR,
		arm.ASUB,
		arm.ASBC,
		arm.ARSB,
		arm.ARSC:
		if p1.Reg == n || (p1.Reg == 0 && p1.To.Type == obj.TYPE_REG && p1.To.Reg == n) {
			if p1.From.Type != obj.TYPE_REG {
				if gc.Debug['P'] != 0 {
					fmt.Printf("\tcan't swap; FAILURE\n")
				}
				return false
			}
//.........這裏部分代碼省略.........

// fuseClear merges memory clear operations.
//
// Looks for this pattern (sequence of clears):
// 	MOVD	R0, n(R15)
// 	MOVD	R0, n+8(R15)
// 	MOVD	R0, n+16(R15)
// Replaces with:
//	CLEAR	$24, n(R15)
func fuseClear(r *gc.Flow) int {
	n := 0
	var align int64
	var clear *obj.Prog
	for ; r != nil; r = r.Link {
		// If there is a branch into the instruction stream then
		// we can't fuse into previous instructions.
		if gc.Uniqp(r) == nil {
			clear = nil
		}

		p := r.Prog
		if p.As == obj.ANOP {
			continue
		}
		if p.As == s390x.AXC {
			if p.From.Reg == p.To.Reg && p.From.Offset == p.To.Offset {
				// TODO(mundaym): merge clears?
				p.As = s390x.ACLEAR
				p.From.Offset = p.From3.Offset
				p.From3 = nil
				p.From.Type = obj.TYPE_CONST
				p.From.Reg = 0
				clear = p
			} else {
				clear = nil
			}
			continue
		}

		// Is our source a constant zero?
		if !isZero(&p.From) {
			clear = nil
			continue
		}

		// Are we moving to memory?
		if p.To.Type != obj.TYPE_MEM ||
			p.To.Index != 0 ||
			p.To.Offset >= 4096 ||
			!(p.To.Name == obj.NAME_NONE || p.To.Name == obj.NAME_AUTO || p.To.Name == obj.NAME_PARAM) {
			clear = nil
			continue
		}

		size := int64(0)
		switch p.As {
		default:
			clear = nil
			continue
		case s390x.AMOVB, s390x.AMOVBZ:
			size = 1
		case s390x.AMOVH, s390x.AMOVHZ:
			size = 2
		case s390x.AMOVW, s390x.AMOVWZ:
			size = 4
		case s390x.AMOVD:
			size = 8
		}

		// doubleword aligned clears should be kept doubleword
		// aligned
		if (size == 8 && align != 8) || (size != 8 && align == 8) {
			clear = nil
		}

		if clear != nil &&
			clear.To.Reg == p.To.Reg &&
			clear.To.Name == p.To.Name &&
			clear.To.Node == p.To.Node &&
			clear.To.Sym == p.To.Sym {

			min := clear.To.Offset
			max := clear.To.Offset + clear.From.Offset

			// previous clear is already clearing this region
			if min <= p.To.Offset && max >= p.To.Offset+size {
				excise(r)
				n++
				continue
			}

			// merge forwards
			if max == p.To.Offset {
				clear.From.Offset += size
				excise(r)
				n++
				continue
			}

			// merge backwards
			if min-size == p.To.Offset {
//.........這裏部分代碼省略.........

// castPropagation tries to eliminate unecessary casts.
//
// For example:
// 	MOVHZ	R1, R2     // uint16
//	MOVB	R2, 0(R15) // int8
// Can be simplified to:
//	MOVB	R1, 0(R15)
func castPropagation(r *gc.Flow) int {
	n := 0
	for ; r != nil; r = r.Link {
		p := r.Prog
		if !isMove(p) || !isGPR(&p.To) {
			continue
		}

		// r is a move with a destination register
		var move *gc.Flow
		for rr := gc.Uniqs(r); rr != nil; rr = gc.Uniqs(rr) {
			if gc.Uniqp(rr) == nil {
				// branch target: leave alone
				break
			}
			pp := rr.Prog
			if isMove(pp) && copyas(&pp.From, &p.To) {
				if pp.To.Type == obj.TYPE_MEM {
					if p.From.Type == obj.TYPE_MEM ||
						p.From.Type == obj.TYPE_ADDR {
						break
					}
					if p.From.Type == obj.TYPE_CONST &&
						int64(int16(p.From.Offset)) != p.From.Offset {
						break
					}
				}
				move = rr
				break
			}
			if pp.As == obj.ANOP {
				continue
			}
			break
		}
		if move == nil {
			continue
		}

		// we have a move that reads from our destination reg, check if any future
		// instructions also read from the reg
		mp := move.Prog
		if !copyas(&mp.From, &mp.To) {
			safe := false
			for rr := gc.Uniqs(move); rr != nil; rr = gc.Uniqs(rr) {
				if gc.Uniqp(rr) == nil {
					break
				}
				switch copyu(rr.Prog, &p.To, nil) {
				case _None:
					continue
				case _Write:
					safe = true
				}
				break
			}
			if !safe {
				continue
			}
		}

		// at this point we have something like:
		// MOV* const/mem/reg, reg
		// MOV* reg, reg/mem
		// now check if this is a cast that cannot be forward propagated
		execute := false
		if p.As == mp.As || isZero(&p.From) || size(p.As) == size(mp.As) {
			execute = true
		} else if isGPR(&p.From) && size(p.As) >= size(mp.As) {
			execute = true
		}

		if execute {
			mp.From = p.From
			excise(r)
			n++
		}
	}
	return n
}

// fuseMultiple merges memory loads and stores into load multiple and
// store multiple operations.
//
// Looks for this pattern (sequence of loads or stores):
// 	MOVD	R1, 0(R15)
//	MOVD	R2, 8(R15)
//	MOVD	R3, 16(R15)
// Replaces with:
//	STMG	R1, R3, 0(R15)
func fuseMultiple(r *gc.Flow) int {
	n := 0
	var fused *obj.Prog
	for ; r != nil; r = r.Link {
		// If there is a branch into the instruction stream then
		// we can't fuse into previous instructions.
		if gc.Uniqp(r) == nil {
			fused = nil
		}

		p := r.Prog

		isStore := isGPR(&p.From) && isBDMem(&p.To)
		isLoad := isGPR(&p.To) && isBDMem(&p.From)

		// are we a candidate?
		size := int64(0)
		switch p.As {
		default:
			fused = nil
			continue
		case obj.ANOP:
			// skip over nops
			continue
		case s390x.AMOVW, s390x.AMOVWZ:
			size = 4
			// TODO(mundaym): 32-bit load multiple is currently not supported
			// as it requires sign/zero extension.
			if !isStore {
				fused = nil
				continue
			}
		case s390x.AMOVD:
			size = 8
			if !isLoad && !isStore {
				fused = nil
				continue
			}
		}

		// If we merge two loads/stores with different source/destination Nodes
		// then we will lose a reference the second Node which means that the
		// compiler might mark the Node as unused and free its slot on the stack.
		// TODO(mundaym): allow this by adding a dummy reference to the Node.
		if fused == nil ||
			fused.From.Node != p.From.Node ||
			fused.From.Type != p.From.Type ||
			fused.To.Node != p.To.Node ||
			fused.To.Type != p.To.Type {
			fused = p
			continue
		}

		// check two addresses
		ca := func(a, b *obj.Addr, offset int64) bool {
			return a.Reg == b.Reg && a.Offset+offset == b.Offset &&
				a.Sym == b.Sym && a.Name == b.Name
		}

		switch fused.As {
		default:
			fused = p
		case s390x.AMOVW, s390x.AMOVWZ:
			if size == 4 && fused.From.Reg+1 == p.From.Reg && ca(&fused.To, &p.To, 4) {
				fused.As = s390x.ASTMY
				fused.Reg = p.From.Reg
				excise(r)
				n++
			} else {
				fused = p
			}
		case s390x.AMOVD:
			if size == 8 && fused.From.Reg+1 == p.From.Reg && ca(&fused.To, &p.To, 8) {
				fused.As = s390x.ASTMG
				fused.Reg = p.From.Reg
				excise(r)
				n++
			} else if size == 8 && fused.To.Reg+1 == p.To.Reg && ca(&fused.From, &p.From, 8) {
				fused.As = s390x.ALMG
				fused.Reg = fused.To.Reg
				fused.To.Reg = p.To.Reg
				excise(r)
				n++
			} else {
				fused = p
			}
		case s390x.ASTMG, s390x.ASTMY:
			if (fused.As == s390x.ASTMY && size != 4) ||
				(fused.As == s390x.ASTMG && size != 8) {
				fused = p
				continue
//.........這裏部分代碼省略.........

// fuseOpMoves looks for moves following 2-operand operations and trys to merge them into
// a 3-operand operation.
//
// For example:
//	ADD R1, R2
//	MOVD R2, R3
// might become
//	ADD R1, R2, R3
func fuseOpMoves(r *gc.Flow) int {
	n := 0
	for ; r != nil; r = r.Link {
		p := r.Prog
		switch p.As {
		case s390x.AADD:
		case s390x.ASUB:
			if isConst(&p.From) && int64(int16(p.From.Offset)) != p.From.Offset {
				continue
			}
		case s390x.ASLW,
			s390x.ASRW,
			s390x.ASRAW,
			s390x.ASLD,
			s390x.ASRD,
			s390x.ASRAD,
			s390x.ARLL,
			s390x.ARLLG:
			// ok - p.From will be a reg or a constant
		case s390x.AOR,
			s390x.AORN,
			s390x.AAND,
			s390x.AANDN,
			s390x.ANAND,
			s390x.ANOR,
			s390x.AXOR,
			s390x.AMULLW,
			s390x.AMULLD:
			if isConst(&p.From) {
				// these instructions can either use 3 register form
				// or have an immediate but not both
				continue
			}
		default:
			continue
		}

		if p.Reg != 0 && p.Reg != p.To.Reg {
			continue
		}

		var move *gc.Flow
		rr := gc.Uniqs(r)
		for {
			if rr == nil || gc.Uniqp(rr) == nil || rr == r {
				break
			}
			pp := rr.Prog
			switch copyu(pp, &p.To, nil) {
			case _None:
				rr = gc.Uniqs(rr)
				continue
			case _Read:
				if move == nil && pp.As == s390x.AMOVD && isGPR(&pp.From) && isGPR(&pp.To) {
					move = rr
					rr = gc.Uniqs(rr)
					continue
				}
			case _Write:
				if move == nil {
					// dead code
					excise(r)
					n++
				} else {
					for prev := gc.Uniqp(move); prev != r; prev = gc.Uniqp(prev) {
						if copyu(prev.Prog, &move.Prog.To, nil) != 0 {
							move = nil
							break
						}
					}
					if move == nil {
						break
					}
					p.Reg, p.To.Reg = p.To.Reg, move.Prog.To.Reg
					excise(move)
					n++

					// clean up
					if p.From.Reg == p.To.Reg && isCommutative(p.As) {
						p.From.Reg, p.Reg = p.Reg, 0
					}
					if p.To.Reg == p.Reg {
						p.Reg = 0
					}
					// we could try again if p has become a 2-operand op
					// but in testing nothing extra was extracted
				}
			}
			break
		}
	}
	return n
//.........這裏部分代碼省略.........