Golang Prog.As方法代碼示例

// Called after regopt and peep have run.
// Expand CHECKNIL pseudo-op into actual nil pointer check.
func expandchecks(firstp *obj.Prog) {
	var p1 *obj.Prog
	var p2 *obj.Prog

	for p := firstp; p != nil; p = p.Link {
		if p.As != obj.ACHECKNIL {
			continue
		}
		if gc.Debug_checknil != 0 && p.Lineno > 1 { // p->lineno==1 in generated wrappers
			gc.Warnl(int(p.Lineno), "generated nil check")
		}

		// check is
		//	CMP arg, $0
		//	JNE 2(PC) (likely)
		//	MOV AX, 0
		p1 = gc.Ctxt.NewProg()

		p2 = gc.Ctxt.NewProg()
		gc.Clearp(p1)
		gc.Clearp(p2)
		p1.Link = p2
		p2.Link = p.Link
		p.Link = p1
		p1.Lineno = p.Lineno
		p2.Lineno = p.Lineno
		p1.Pc = 9999
		p2.Pc = 9999
		p.As = int16(cmpptr)
		p.To.Type = obj.TYPE_CONST
		p.To.Offset = 0
		p1.As = x86.AJNE
		p1.From.Type = obj.TYPE_CONST
		p1.From.Offset = 1 // likely
		p1.To.Type = obj.TYPE_BRANCH
		p1.To.Val = p2.Link

		// crash by write to memory address 0.
		// if possible, since we know arg is 0, use 0(arg),
		// which will be shorter to encode than plain 0.
		p2.As = x86.AMOVL

		p2.From.Type = obj.TYPE_REG
		p2.From.Reg = x86.REG_AX
		if regtyp(&p.From) {
			p2.To.Type = obj.TYPE_MEM
			p2.To.Reg = p.From.Reg
		} else {
			p2.To.Type = obj.TYPE_MEM
			p2.To.Reg = x86.REG_NONE
		}

		p2.To.Offset = 0
	}
}

func rewriteToPcrel(ctxt *obj.Link, p *obj.Prog) {
	// RegTo2 is set on the instructions we insert here so they don't get
	// processed twice.
	if p.RegTo2 != 0 {
		return
	}
	if p.As == obj.ATEXT || p.As == obj.AFUNCDATA || p.As == obj.ACALL || p.As == obj.ARET || p.As == obj.AJMP {
		return
	}
	// Any Prog (aside from the above special cases) with an Addr with Name ==
	// NAME_EXTERN, NAME_STATIC or NAME_GOTREF has a CALL __x86.get_pc_thunk.cx
	// inserted before it.
	isName := func(a *obj.Addr) bool {
		if a.Sym == nil || (a.Type != obj.TYPE_MEM && a.Type != obj.TYPE_ADDR) || a.Reg != 0 {
			return false
		}
		if a.Sym.Type == obj.STLSBSS {
			return false
		}
		return a.Name == obj.NAME_EXTERN || a.Name == obj.NAME_STATIC || a.Name == obj.NAME_GOTREF
	}

	if isName(&p.From) && p.From.Type == obj.TYPE_ADDR {
		// Handle things like "MOVL $sym, (SP)" or "PUSHL $sym" by rewriting
		// to "MOVL $sym, CX; MOVL CX, (SP)" or "MOVL $sym, CX; PUSHL CX"
		// respectively.
		if p.To.Type != obj.TYPE_REG {
			q := obj.Appendp(ctxt, p)
			q.As = p.As
			q.From.Type = obj.TYPE_REG
			q.From.Reg = REG_CX
			q.To = p.To
			p.As = AMOVL
			p.To.Type = obj.TYPE_REG
			p.To.Reg = REG_CX
			p.To.Sym = nil
			p.To.Name = obj.NAME_NONE
		}
	}

	if !isName(&p.From) && !isName(&p.To) && (p.From3 == nil || !isName(p.From3)) {
		return
	}
	q := obj.Appendp(ctxt, p)
	q.RegTo2 = 1
	r := obj.Appendp(ctxt, q)
	r.RegTo2 = 1
	q.As = obj.ACALL
	q.To.Sym = obj.Linklookup(ctxt, "__x86.get_pc_thunk.cx", 0)
	q.To.Type = obj.TYPE_MEM
	q.To.Name = obj.NAME_EXTERN
	q.To.Sym.Local = true
	r.As = p.As
	r.Scond = p.Scond
	r.From = p.From
	r.From3 = p.From3
	r.Reg = p.Reg
	r.To = p.To
	obj.Nopout(p)
}

func Prog(as int) *obj.Prog {
	var p *obj.Prog

	if as == obj.ADATA || as == obj.AGLOBL {
		if ddumped != 0 {
			Fatalf("already dumped data")
		}
		if dpc == nil {
			dpc = Ctxt.NewProg()
			dfirst = dpc
		}

		p = dpc
		dpc = Ctxt.NewProg()
		p.Link = dpc
	} else {
		p = Pc
		Pc = Ctxt.NewProg()
		Clearp(Pc)
		p.Link = Pc
	}

	if lineno == 0 {
		if Debug['K'] != 0 {
			Warn("prog: line 0")
		}
	}

	p.As = int16(as)
	p.Lineno = lineno
	return p
}

// ARMConditionCodes handles the special condition code situation for the ARM.
// It returns a boolean to indicate success; failure means cond was unrecognized.
func ARMConditionCodes(prog *obj.Prog, cond string) bool {
	if cond == "" {
		return true
	}
	bits, ok := ParseARMCondition(cond)
	if !ok {
		return false
	}
	/* hack to make B.NE etc. work: turn it into the corresponding conditional */
	if prog.As == arm.AB {
		prog.As = int16(bcode[(bits^arm.C_SCOND_XOR)&0xf])
		bits = (bits &^ 0xf) | arm.C_SCOND_NONE
	}
	prog.Scond = bits
	return true
}

func peep(firstp *obj.Prog) {
	g := gc.Flowstart(firstp, nil)
	if g == nil {
		return
	}
	gactive = 0

	// byte, word arithmetic elimination.
	elimshortmov(g)

	// constant propagation
	// find MOV $con,R followed by
	// another MOV $con,R without
	// setting R in the interim
	var p *obj.Prog
	for r := g.Start; r != nil; r = r.Link {
		p = r.Prog
		switch p.As {
		case x86.ALEAL:
			if regtyp(&p.To) {
				if p.From.Sym != nil {
					if p.From.Index == x86.REG_NONE {
						conprop(r)
					}
				}
			}

		case x86.AMOVB,
			x86.AMOVW,
			x86.AMOVL,
			x86.AMOVSS,
			x86.AMOVSD:
			if regtyp(&p.To) {
				if p.From.Type == obj.TYPE_CONST || p.From.Type == obj.TYPE_FCONST {
					conprop(r)
				}
			}
		}
	}

	var r1 *gc.Flow
	var p1 *obj.Prog
	var r *gc.Flow
	var t int
loop1:
	if gc.Debug['P'] != 0 && gc.Debug['v'] != 0 {
		gc.Dumpit("loop1", g.Start, 0)
	}

	t = 0
	for r = g.Start; r != nil; r = r.Link {
		p = r.Prog
		switch p.As {
		case x86.AMOVL,
			x86.AMOVSS,
			x86.AMOVSD:
			if regtyp(&p.To) {
				if regtyp(&p.From) {
					if copyprop(g, r) {
						excise(r)
						t++
					} else if subprop(r) && copyprop(g, r) {
						excise(r)
						t++
					}
				}
			}

		case x86.AMOVBLZX,
			x86.AMOVWLZX,
			x86.AMOVBLSX,
			x86.AMOVWLSX:
			if regtyp(&p.To) {
				r1 = rnops(gc.Uniqs(r))
				if r1 != nil {
					p1 = r1.Prog
					if p.As == p1.As && p.To.Type == p1.From.Type && p.To.Reg == p1.From.Reg {
						p1.As = x86.AMOVL
						t++
					}
				}
			}

		case x86.AADDL,
			x86.AADDW:
			if p.From.Type != obj.TYPE_CONST || needc(p.Link) {
				break
			}
			if p.From.Offset == -1 {
				if p.As == x86.AADDL {
					p.As = x86.ADECL
				} else {
					p.As = x86.ADECW
				}
				p.From = obj.Addr{}
				break
			}

			if p.From.Offset == 1 {
				if p.As == x86.AADDL {
//.........這裏部分代碼省略.........

// Rewrite p, if necessary, to access global data via the global offset table.
func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog) {
	var add, lea, mov, reg int16
	if p.Mode == 64 {
		add = AADDQ
		lea = ALEAQ
		mov = AMOVQ
		reg = REG_R15
	} else {
		add = AADDL
		lea = ALEAL
		mov = AMOVL
		reg = REG_CX
	}

	if p.As == obj.ADUFFCOPY || p.As == obj.ADUFFZERO {
		//     ADUFFxxx $offset
		// becomes
		//     $MOV [email protected], $reg
		//     $ADD $offset, $reg
		//     CALL $reg
		var sym *obj.LSym
		if p.As == obj.ADUFFZERO {
			sym = obj.Linklookup(ctxt, "runtime.duffzero", 0)
		} else {
			sym = obj.Linklookup(ctxt, "runtime.duffcopy", 0)
		}
		offset := p.To.Offset
		p.As = mov
		p.From.Type = obj.TYPE_MEM
		p.From.Name = obj.NAME_GOTREF
		p.From.Sym = sym
		p.To.Type = obj.TYPE_REG
		p.To.Reg = reg
		p.To.Offset = 0
		p.To.Sym = nil
		p1 := obj.Appendp(ctxt, p)
		p1.As = add
		p1.From.Type = obj.TYPE_CONST
		p1.From.Offset = offset
		p1.To.Type = obj.TYPE_REG
		p1.To.Reg = reg
		p2 := obj.Appendp(ctxt, p1)
		p2.As = obj.ACALL
		p2.To.Type = obj.TYPE_REG
		p2.To.Reg = reg
	}

	// We only care about global data: NAME_EXTERN means a global
	// symbol in the Go sense, and p.Sym.Local is true for a few
	// internally defined symbols.
	if p.As == lea && p.From.Type == obj.TYPE_MEM && p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local {
		// $LEA sym, Rx becomes $MOV $sym, Rx which will be rewritten below
		p.As = mov
		p.From.Type = obj.TYPE_ADDR
	}
	if p.From.Type == obj.TYPE_ADDR && p.From.Name == obj.NAME_EXTERN && !p.From.Sym.Local {
		// $MOV $sym, Rx becomes $MOV [email protected], Rx
		// $MOV $sym+<off>, Rx becomes $MOV [email protected], Rx; $ADD <off>, Rx
		// On 386 only, more complicated things like PUSHL $sym become $MOV [email protected], CX; PUSHL CX
		cmplxdest := false
		pAs := p.As
		var dest obj.Addr
		if p.To.Type != obj.TYPE_REG || pAs != mov {
			if p.Mode == 64 {
				ctxt.Diag("do not know how to handle LEA-type insn to non-register in %v with -dynlink", p)
			}
			cmplxdest = true
			dest = p.To
			p.As = mov
			p.To.Type = obj.TYPE_REG
			p.To.Reg = REG_CX
			p.To.Sym = nil
			p.To.Name = obj.NAME_NONE
		}
		p.From.Type = obj.TYPE_MEM
		p.From.Name = obj.NAME_GOTREF
		q := p
		if p.From.Offset != 0 {
			q = obj.Appendp(ctxt, p)
			q.As = add
			q.From.Type = obj.TYPE_CONST
			q.From.Offset = p.From.Offset
			q.To = p.To
			p.From.Offset = 0
		}
		if cmplxdest {
			q = obj.Appendp(ctxt, q)
			q.As = pAs
			q.To = dest
			q.From.Type = obj.TYPE_REG
			q.From.Reg = REG_CX
		}
	}
	if p.From3 != nil && p.From3.Name == obj.NAME_EXTERN {
		ctxt.Diag("don't know how to handle %v with -dynlink", p)
	}
	var source *obj.Addr
	// MOVx sym, Ry becomes $MOV [email protected], R15; MOVx (R15), Ry
	// MOVx Ry, sym becomes $MOV [email protected], R15; MOVx Ry, (R15)
//.........這裏部分代碼省略.........

func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
	ctxt.Cursym = cursym

	if cursym.Text == nil || cursym.Text.Link == nil {
		return
	}

	p := cursym.Text
	textstksiz := p.To.Offset
	aoffset := int32(textstksiz)

	cursym.Args = p.To.Val.(int32)
	cursym.Locals = int32(textstksiz)

	/*
	 * find leaf subroutines
	 * strip NOPs
	 * expand RET
	 */
	ctxt.Bso.Flush()
	q := (*obj.Prog)(nil)
	var q1 *obj.Prog
	for p := cursym.Text; p != nil; p = p.Link {
		switch p.As {
		case obj.ATEXT:
			p.Mark |= LEAF

		case obj.ARET:
			break

		case obj.ANOP:
			q1 = p.Link
			q.Link = q1 /* q is non-nop */
			q1.Mark |= p.Mark
			continue

		case ABL,
			obj.ADUFFZERO,
			obj.ADUFFCOPY:
			cursym.Text.Mark &^= LEAF
			fallthrough

		case ACBNZ,
			ACBZ,
			ACBNZW,
			ACBZW,
			ATBZ,
			ATBNZ,
			AB,
			ABEQ,
			ABNE,
			ABCS,
			ABHS,
			ABCC,
			ABLO,
			ABMI,
			ABPL,
			ABVS,
			ABVC,
			ABHI,
			ABLS,
			ABGE,
			ABLT,
			ABGT,
			ABLE,
			AADR, /* strange */
			AADRP:
			q1 = p.Pcond

			if q1 != nil {
				for q1.As == obj.ANOP {
					q1 = q1.Link
					p.Pcond = q1
				}
			}

			break
		}

		q = p
	}

	var o int
	var q2 *obj.Prog
	var retjmp *obj.LSym
	for p := cursym.Text; p != nil; p = p.Link {
		o = int(p.As)
		switch o {
		case obj.ATEXT:
			cursym.Text = p
			if textstksiz < 0 {
				ctxt.Autosize = 0
			} else {
				ctxt.Autosize = int32(textstksiz + 8)
			}
			if (cursym.Text.Mark&LEAF != 0) && ctxt.Autosize <= 8 {
				ctxt.Autosize = 0
			} else if ctxt.Autosize&(16-1) != 0 {
				// The frame includes an LR.
				// If the frame size is 8, it's only an LR,
//.........這裏部分代碼省略.........

func span0(ctxt *obj.Link, cursym *obj.LSym) {
	p := cursym.Text
	if p == nil || p.Link == nil { // handle external functions and ELF section symbols
		return
	}
	ctxt.Cursym = cursym
	ctxt.Autosize = int32(p.To.Offset + 8)

	if oprange[AOR&obj.AMask].start == nil {
		buildop(ctxt)
	}

	c := int64(0)
	p.Pc = c

	var m int
	var o *Optab
	for p = p.Link; p != nil; p = p.Link {
		ctxt.Curp = p
		p.Pc = c
		o = oplook(ctxt, p)
		m = int(o.size)
		if m == 0 {
			if p.As != obj.ANOP && p.As != obj.AFUNCDATA && p.As != obj.APCDATA && p.As != obj.AUSEFIELD {
				ctxt.Diag("zero-width instruction\n%v", p)
			}
			continue
		}

		c += int64(m)
	}

	cursym.Size = c

	/*
	 * if any procedure is large enough to
	 * generate a large SBRA branch, then
	 * generate extra passes putting branches
	 * around jmps to fix. this is rare.
	 */
	bflag := 1

	var otxt int64
	var q *obj.Prog
	for bflag != 0 {
		if ctxt.Debugvlog != 0 {
			fmt.Fprintf(ctxt.Bso, "%5.2f span1\n", obj.Cputime())
		}
		bflag = 0
		c = 0
		for p = cursym.Text.Link; p != nil; p = p.Link {
			p.Pc = c
			o = oplook(ctxt, p)

			// very large conditional branches
			if o.type_ == 6 && p.Pcond != nil {
				otxt = p.Pcond.Pc - c
				if otxt < -(1<<17)+10 || otxt >= (1<<17)-10 {
					q = ctxt.NewProg()
					q.Link = p.Link
					p.Link = q
					q.As = AJMP
					q.Lineno = p.Lineno
					q.To.Type = obj.TYPE_BRANCH
					q.Pcond = p.Pcond
					p.Pcond = q
					q = ctxt.NewProg()
					q.Link = p.Link
					p.Link = q
					q.As = AJMP
					q.Lineno = p.Lineno
					q.To.Type = obj.TYPE_BRANCH
					q.Pcond = q.Link.Link

					addnop(ctxt, p.Link)
					addnop(ctxt, p)
					bflag = 1
				}
			}

			m = int(o.size)
			if m == 0 {
				if p.As != obj.ANOP && p.As != obj.AFUNCDATA && p.As != obj.APCDATA && p.As != obj.AUSEFIELD {
					ctxt.Diag("zero-width instruction\n%v", p)
				}
				continue
			}

			c += int64(m)
		}

		cursym.Size = c
	}

	c += -c & (FuncAlign - 1)
	cursym.Size = c

	/*
	 * lay out the code, emitting code and data relocations.
	 */
//.........這裏部分代碼省略.........

func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
	autosize := int32(0)

	ctxt.Cursym = cursym

	if cursym.Text == nil || cursym.Text.Link == nil {
		return
	}

	softfloat(ctxt, cursym)

	p := cursym.Text
	autoffset := int32(p.To.Offset)
	if autoffset < 0 {
		autoffset = 0
	}
	cursym.Locals = autoffset
	cursym.Args = p.To.Val.(int32)

	/*
	 * find leaf subroutines
	 * strip NOPs
	 * expand RET
	 * expand BECOME pseudo
	 */
	var q1 *obj.Prog
	var q *obj.Prog
	for p := cursym.Text; p != nil; p = p.Link {
		switch p.As {
		case obj.ATEXT:
			p.Mark |= LEAF

		case obj.ARET:
			break

		case ADIV, ADIVU, AMOD, AMODU:
			q = p
			if ctxt.Sym_div == nil {
				initdiv(ctxt)
			}
			cursym.Text.Mark &^= LEAF
			continue

		case obj.ANOP:
			q1 = p.Link
			q.Link = q1 /* q is non-nop */
			if q1 != nil {
				q1.Mark |= p.Mark
			}
			continue

		case ABL,
			ABX,
			obj.ADUFFZERO,
			obj.ADUFFCOPY:
			cursym.Text.Mark &^= LEAF
			fallthrough

		case AB,
			ABEQ,
			ABNE,
			ABCS,
			ABHS,
			ABCC,
			ABLO,
			ABMI,
			ABPL,
			ABVS,
			ABVC,
			ABHI,
			ABLS,
			ABGE,
			ABLT,
			ABGT,
			ABLE:
			q1 = p.Pcond
			if q1 != nil {
				for q1.As == obj.ANOP {
					q1 = q1.Link
					p.Pcond = q1
				}
			}
		}

		q = p
	}

	var o int
	var p1 *obj.Prog
	var p2 *obj.Prog
	var q2 *obj.Prog
	for p := cursym.Text; p != nil; p = p.Link {
		o = int(p.As)
		switch o {
		case obj.ATEXT:
			autosize = int32(p.To.Offset + 4)
			if autosize <= 4 {
				if cursym.Text.Mark&LEAF != 0 {
					p.To.Offset = -4
					autosize = 0
//.........這裏部分代碼省略.........

/*
 * 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 := (*obj.Prog)(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 := int(int(p.To.Reg))
	a := obj.Addr(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 := (*gc.Flow)(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 int(p1.Reg) == n || (p1.Reg == 0 && p1.To.Type == obj.TYPE_REG && int(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.........

func Clearp(p *obj.Prog) {
	obj.Nopout(p)
	p.As = obj.AEND
	p.Pc = int64(pcloc)
	pcloc++
}

//.........這裏部分代碼省略.........
	 */
	var p *obj.Prog
	var q *obj.Prog
	for s, p = sch[:], p0; -cap(s) <= -cap(se); s, p = s[1:], q {
		q = p.Link
		if q != s[0].p.Link {
			*p = s[0].p
			p.Link = q
		}
		for s[0].nop != 0 {
			s[0].nop--
			addnop(ctxt, p)
		}
	}
}

func markregused(ctxt *obj.Link, s *Sch) {
	p := &s.p
	s.comp = compound(ctxt, p)
	s.nop = 0
	if s.comp {
		s.set.ireg |= 1 << (REGTMP - REG_R0)
		s.used.ireg |= 1 << (REGTMP - REG_R0)
	}

	ar := 0  /* dest is really reference */
	ad := 0  /* source/dest is really address */
	ld := 0  /* opcode is load instruction */
	sz := 20 /* size of load/store for overlap computation */

	/*
	 * flags based on opcode
	 */
	switch p.As {
	case obj.ATEXT:
		ctxt.Autosize = int32(p.To.Offset + 8)
		ad = 1

	case AJAL:
		c := p.Reg
		if c == 0 {
			c = REGLINK
		}
		s.set.ireg |= 1 << uint(c-REG_R0)
		ar = 1
		ad = 1

	case ABGEZAL,
		ABLTZAL:
		s.set.ireg |= 1 << (REGLINK - REG_R0)
		fallthrough
	case ABEQ,
		ABGEZ,
		ABGTZ,
		ABLEZ,
		ABLTZ,
		ABNE:
		ar = 1
		ad = 1

	case ABFPT,
		ABFPF:
		ad = 1
		s.used.cc |= E_FCR

	case ACMPEQD,

// movb elimination.
// movb is simulated by the linker
// when a register other than ax, bx, cx, dx
// is used, so rewrite to other instructions
// when possible.  a movb into a register
// can smash the entire 32-bit register without
// causing any trouble.
//
// TODO: Using the Q forms here instead of the L forms
// seems unnecessary, and it makes the instructions longer.
func elimshortmov(g *gc.Graph) {
	var p *obj.Prog

	for r := (*gc.Flow)(g.Start); r != nil; r = r.Link {
		p = r.Prog
		if regtyp(&p.To) {
			switch p.As {
			case x86.AINCB,
				x86.AINCW:
				p.As = x86.AINCQ

			case x86.ADECB,
				x86.ADECW:
				p.As = x86.ADECQ

			case x86.ANEGB,
				x86.ANEGW:
				p.As = x86.ANEGQ

			case x86.ANOTB,
				x86.ANOTW:
				p.As = x86.ANOTQ
			}

			if regtyp(&p.From) || p.From.Type == obj.TYPE_CONST {
				// move or artihmetic into partial register.
				// from another register or constant can be movl.
				// we don't switch to 64-bit arithmetic if it can
				// change how the carry bit is set (and the carry bit is needed).
				switch p.As {
				case x86.AMOVB,
					x86.AMOVW:
					p.As = x86.AMOVQ

				case x86.AADDB,
					x86.AADDW:
					if !needc(p.Link) {
						p.As = x86.AADDQ
					}

				case x86.ASUBB,
					x86.ASUBW:
					if !needc(p.Link) {
						p.As = x86.ASUBQ
					}

				case x86.AMULB,
					x86.AMULW:
					p.As = x86.AMULQ

				case x86.AIMULB,
					x86.AIMULW:
					p.As = x86.AIMULQ

				case x86.AANDB,
					x86.AANDW:
					p.As = x86.AANDQ

				case x86.AORB,
					x86.AORW:
					p.As = x86.AORQ

				case x86.AXORB,
					x86.AXORW:
					p.As = x86.AXORQ

				case x86.ASHLB,
					x86.ASHLW:
					p.As = x86.ASHLQ
				}
			} else if p.From.Type != obj.TYPE_REG {
				// explicit zero extension, but don't
				// do that if source is a byte register
				// (only AH can occur and it's forbidden).
				switch p.As {
				case x86.AMOVB:
					p.As = x86.AMOVBQZX

				case x86.AMOVW:
					p.As = x86.AMOVWQZX
				}
			}
		}
	}
}

func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog {
	// MOVV	g_stackguard(g), R1
	p = obj.Appendp(ctxt, p)

	p.As = AMOVV
	p.From.Type = obj.TYPE_MEM
	p.From.Reg = REGG
	p.From.Offset = 2 * int64(ctxt.Arch.Ptrsize) // G.stackguard0
	if ctxt.Cursym.Cfunc != 0 {
		p.From.Offset = 3 * int64(ctxt.Arch.Ptrsize) // G.stackguard1
	}
	p.To.Type = obj.TYPE_REG
	p.To.Reg = REG_R1

	var q *obj.Prog
	if framesize <= obj.StackSmall {
		// small stack: SP < stackguard
		//	AGTU	SP, stackguard, R1
		p = obj.Appendp(ctxt, p)

		p.As = ASGTU
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REGSP
		p.Reg = REG_R1
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REG_R1
	} else if framesize <= obj.StackBig {
		// large stack: SP-framesize < stackguard-StackSmall
		//	ADDV	$-framesize, SP, R2
		//	SGTU	R2, stackguard, R1
		p = obj.Appendp(ctxt, p)

		p.As = AADDV
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = int64(-framesize)
		p.Reg = REGSP
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REG_R2

		p = obj.Appendp(ctxt, p)
		p.As = ASGTU
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REG_R2
		p.Reg = REG_R1
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REG_R1
	} else {
		// Such a large stack we need to protect against wraparound.
		// If SP is close to zero:
		//	SP-stackguard+StackGuard <= framesize + (StackGuard-StackSmall)
		// The +StackGuard on both sides is required to keep the left side positive:
		// SP is allowed to be slightly below stackguard. See stack.h.
		//
		// Preemption sets stackguard to StackPreempt, a very large value.
		// That breaks the math above, so we have to check for that explicitly.
		//	// stackguard is R1
		//	MOVV	$StackPreempt, R2
		//	BEQ	R1, R2, label-of-call-to-morestack
		//	ADDV	$StackGuard, SP, R2
		//	SUBVU	R1, R2
		//	MOVV	$(framesize+(StackGuard-StackSmall)), R1
		//	SGTU	R2, R1, R1
		p = obj.Appendp(ctxt, p)

		p.As = AMOVV
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = obj.StackPreempt
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REG_R2

		p = obj.Appendp(ctxt, p)
		q = p
		p.As = ABEQ
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REG_R1
		p.Reg = REG_R2
		p.To.Type = obj.TYPE_BRANCH
		p.Mark |= BRANCH

		p = obj.Appendp(ctxt, p)
		p.As = AADDV
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = obj.StackGuard
		p.Reg = REGSP
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REG_R2

		p = obj.Appendp(ctxt, p)
		p.As = ASUBVU
		p.From.Type = obj.TYPE_REG
		p.From.Reg = REG_R1
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REG_R2

		p = obj.Appendp(ctxt, p)
		p.As = AMOVV
		p.From.Type = obj.TYPE_CONST
		p.From.Offset = int64(framesize) + obj.StackGuard - obj.StackSmall
		p.To.Type = obj.TYPE_REG
		p.To.Reg = REG_R1
//.........這裏部分代碼省略.........

func progedit(ctxt *obj.Link, p *obj.Prog) {
	p.From.Class = 0
	p.To.Class = 0

	// Rewrite JMP/JAL to symbol as TYPE_BRANCH.
	switch p.As {
	case AJMP,
		AJAL,
		ARET,
		obj.ADUFFZERO,
		obj.ADUFFCOPY:
		if p.To.Sym != nil {
			p.To.Type = obj.TYPE_BRANCH
		}
	}

	// Rewrite float constants to values stored in memory.
	switch p.As {
	case AMOVF:
		if p.From.Type == obj.TYPE_FCONST {
			f32 := float32(p.From.Val.(float64))
			i32 := math.Float32bits(f32)
			literal := fmt.Sprintf("$f32.%08x", i32)
			s := obj.Linklookup(ctxt, literal, 0)
			s.Size = 4
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = s
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
		}

	case AMOVD:
		if p.From.Type == obj.TYPE_FCONST {
			i64 := math.Float64bits(p.From.Val.(float64))
			literal := fmt.Sprintf("$f64.%016x", i64)
			s := obj.Linklookup(ctxt, literal, 0)
			s.Size = 8
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = s
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
		}

		// Put >32-bit constants in memory and load them
	case AMOVV:
		if p.From.Type == obj.TYPE_CONST && p.From.Name == obj.NAME_NONE && p.From.Reg == 0 && int64(int32(p.From.Offset)) != p.From.Offset {
			literal := fmt.Sprintf("$i64.%016x", uint64(p.From.Offset))
			s := obj.Linklookup(ctxt, literal, 0)
			s.Size = 8
			p.From.Type = obj.TYPE_MEM
			p.From.Sym = s
			p.From.Name = obj.NAME_EXTERN
			p.From.Offset = 0
		}
	}

	// Rewrite SUB constants into ADD.
	switch p.As {
	case ASUB:
		if p.From.Type == obj.TYPE_CONST {
			p.From.Offset = -p.From.Offset
			p.As = AADD
		}

	case ASUBU:
		if p.From.Type == obj.TYPE_CONST {
			p.From.Offset = -p.From.Offset
			p.As = AADDU
		}

	case ASUBV:
		if p.From.Type == obj.TYPE_CONST {
			p.From.Offset = -p.From.Offset
			p.As = AADDV
		}

	case ASUBVU:
		if p.From.Type == obj.TYPE_CONST {
			p.From.Offset = -p.From.Offset
			p.As = AADDVU
		}
	}
}