github.com/miolini/go@v0.0.0-20160405192216-fca68c8cb408/src/cmd/compile/internal/ppc64/peep.go

// Derived from Inferno utils/6c/peep.c
// http://code.google.com/p/inferno-os/source/browse/utils/6c/peep.c
//
//	Copyright © 1994-1999 Lucent Technologies Inc.  All rights reserved.
//	Portions Copyright © 1995-1997 C H Forsyth (forsyth@terzarima.net)
//	Portions Copyright © 1997-1999 Vita Nuova Limited
//	Portions Copyright © 2000-2007 Vita Nuova Holdings Limited (www.vitanuova.com)
//	Portions Copyright © 2004,2006 Bruce Ellis
//	Portions Copyright © 2005-2007 C H Forsyth (forsyth@terzarima.net)
//	Revisions Copyright © 2000-2007 Lucent Technologies Inc. and others
//	Portions Copyright © 2009 The Go Authors.  All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

package ppc64

import (
	"cmd/compile/internal/gc"
	"cmd/internal/obj"
	"cmd/internal/obj/ppc64"
	"fmt"
)

var gactive uint32

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

	var p *obj.Prog
	var r *gc.Flow
	var t obj.As
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

		// TODO(austin) Handle smaller moves.  arm and amd64
		// distinguish between moves that moves that *must*
		// sign/zero extend and moves that don't care so they
		// can eliminate moves that don't care without
		// breaking moves that do care. This might let us
		// simplify or remove the next peep loop, too.
		if p.As == ppc64.AMOVD || p.As == ppc64.AFMOVD {
			if regtyp(&p.To) {
				// Try to eliminate reg->reg moves
				if regtyp(&p.From) {
					if p.From.Type == p.To.Type {
						if copyprop(r) {
							excise(r)
							t++
						} else if subprop(r) && copyprop(r) {
							excise(r)
							t++
						}
					}
				}

				// Convert uses to $0 to uses of R0 and
				// propagate R0
				if regzer(&p.From) {
					if p.To.Type == obj.TYPE_REG {
						p.From.Type = obj.TYPE_REG
						p.From.Reg = ppc64.REGZERO
						if copyprop(r) {
							excise(r)
							t++
						} else if subprop(r) && copyprop(r) {
							excise(r)
							t++
						}
					}
				}
			}
		}
	}

	if t != 0 {
		goto loop1
	}

	/*
	 * look for MOVB x,R; MOVB R,R (for small MOVs not handled above)
	 */
	var p1 *obj.Prog
	var r1 *gc.Flow
	for r := g.Start; r != nil; r = r.Link {
		p = r.Prog
		switch p.As {
		default:
			continue

		case ppc64.AMOVH,
			ppc64.AMOVHZ,
			ppc64.AMOVB,
			ppc64.AMOVBZ,
			ppc64.AMOVW,
			ppc64.AMOVWZ:
			if p.To.Type != obj.TYPE_REG {
				continue
			}
		}

		r1 = r.Link
		if r1 == nil {
			continue
		}
		p1 = r1.Prog
		if p1.As != p.As {
			continue
		}
		if p1.From.Type != obj.TYPE_REG || p1.From.Reg != p.To.Reg {
			continue
		}
		if p1.To.Type != obj.TYPE_REG || p1.To.Reg != p.To.Reg {
			continue
		}
		excise(r1)
	}

	if gc.Debug['D'] > 1 {
		goto ret /* allow following code improvement to be suppressed */
	}

	/*
	 * look for OP x,y,R; CMP R, $0 -> OPCC x,y,R
	 * when OP can set condition codes correctly
	 */
	for r := g.Start; r != nil; r = r.Link {
		p = r.Prog
		switch p.As {
		case ppc64.ACMP,
			ppc64.ACMPW: /* always safe? */
			if !regzer(&p.To) {
				continue
			}
			r1 = r.S1
			if r1 == nil {
				continue
			}
			switch r1.Prog.As {
			default:
				continue

				/* the conditions can be complex and these are currently little used */
			case ppc64.ABCL,
				ppc64.ABC:
				continue

			case ppc64.ABEQ,
				ppc64.ABGE,
				ppc64.ABGT,
				ppc64.ABLE,
				ppc64.ABLT,
				ppc64.ABNE,
				ppc64.ABVC,
				ppc64.ABVS:
				break
			}

			r1 = r
			for {
				r1 = gc.Uniqp(r1)
				if r1 == nil || r1.Prog.As != obj.ANOP {
					break
				}
			}

			if r1 == nil {
				continue
			}
			p1 = r1.Prog
			if p1.To.Type != obj.TYPE_REG || p1.To.Reg != p.From.Reg {
				continue
			}
			switch p1.As {
			/* irregular instructions */
			case ppc64.ASUB,
				ppc64.AADD,
				ppc64.AXOR,
				ppc64.AOR:
				if p1.From.Type == obj.TYPE_CONST || p1.From.Type == obj.TYPE_ADDR {
					continue
				}
			}

			switch p1.As {
			default:
				continue

			case ppc64.AMOVW,
				ppc64.AMOVD:
				if p1.From.Type != obj.TYPE_REG {
					continue
				}
				continue

			case ppc64.AANDCC,
				ppc64.AANDNCC,
				ppc64.AORCC,
				ppc64.AORNCC,
				ppc64.AXORCC,
				ppc64.ASUBCC,
				ppc64.ASUBECC,
				ppc64.ASUBMECC,
				ppc64.ASUBZECC,
				ppc64.AADDCC,
				ppc64.AADDCCC,
				ppc64.AADDECC,
				ppc64.AADDMECC,
				ppc64.AADDZECC,
				ppc64.ARLWMICC,
				ppc64.ARLWNMCC,
				/* don't deal with floating point instructions for now */
				/*
					case AFABS:
					case AFADD:
					case AFADDS:
					case AFCTIW:
					case AFCTIWZ:
					case AFDIV:
					case AFDIVS:
					case AFMADD:
					case AFMADDS:
					case AFMOVD:
					case AFMSUB:
					case AFMSUBS:
					case AFMUL:
					case AFMULS:
					case AFNABS:
					case AFNEG:
					case AFNMADD:
					case AFNMADDS:
					case AFNMSUB:
					case AFNMSUBS:
					case AFRSP:
					case AFSUB:
					case AFSUBS:
					case ACNTLZW:
					case AMTFSB0:
					case AMTFSB1:
				*/
				ppc64.AADD,
				ppc64.AADDV,
				ppc64.AADDC,
				ppc64.AADDCV,
				ppc64.AADDME,
				ppc64.AADDMEV,
				ppc64.AADDE,
				ppc64.AADDEV,
				ppc64.AADDZE,
				ppc64.AADDZEV,
				ppc64.AAND,
				ppc64.AANDN,
				ppc64.ADIVW,
				ppc64.ADIVWV,
				ppc64.ADIVWU,
				ppc64.ADIVWUV,
				ppc64.ADIVD,
				ppc64.ADIVDV,
				ppc64.ADIVDU,
				ppc64.ADIVDUV,
				ppc64.AEQV,
				ppc64.AEXTSB,
				ppc64.AEXTSH,
				ppc64.AEXTSW,
				ppc64.AMULHW,
				ppc64.AMULHWU,
				ppc64.AMULLW,
				ppc64.AMULLWV,
				ppc64.AMULHD,
				ppc64.AMULHDU,
				ppc64.AMULLD,
				ppc64.AMULLDV,
				ppc64.ANAND,
				ppc64.ANEG,
				ppc64.ANEGV,
				ppc64.ANOR,
				ppc64.AOR,
				ppc64.AORN,
				ppc64.AREM,
				ppc64.AREMV,
				ppc64.AREMU,
				ppc64.AREMUV,
				ppc64.AREMD,
				ppc64.AREMDV,
				ppc64.AREMDU,
				ppc64.AREMDUV,
				ppc64.ARLWMI,
				ppc64.ARLWNM,
				ppc64.ASLW,
				ppc64.ASRAW,
				ppc64.ASRW,
				ppc64.ASLD,
				ppc64.ASRAD,
				ppc64.ASRD,
				ppc64.ASUB,
				ppc64.ASUBV,
				ppc64.ASUBC,
				ppc64.ASUBCV,
				ppc64.ASUBME,
				ppc64.ASUBMEV,
				ppc64.ASUBE,
				ppc64.ASUBEV,
				ppc64.ASUBZE,
				ppc64.ASUBZEV,
				ppc64.AXOR:
				t = variant2as(p1.As, as2variant(p1.As)|V_CC)
			}

			if gc.Debug['D'] != 0 {
				fmt.Printf("cmp %v; %v -> ", p1, p)
			}
			p1.As = t
			if gc.Debug['D'] != 0 {
				fmt.Printf("%v\n", p1)
			}
			excise(r)
			continue
		}
	}

ret:
	gc.Flowend(g)
}

func excise(r *gc.Flow) {
	p := r.Prog
	if gc.Debug['P'] != 0 && gc.Debug['v'] != 0 {
		fmt.Printf("%v ===delete===\n", p)
	}
	obj.Nopout(p)
	gc.Ostats.Ndelmov++
}

// regzer returns true if a's value is 0 (a is R0 or $0)
func regzer(a *obj.Addr) bool {
	if a.Type == obj.TYPE_CONST || a.Type == obj.TYPE_ADDR {
		if a.Sym == nil && a.Reg == 0 {
			if a.Offset == 0 {
				return true
			}
		}
	}
	return a.Type == obj.TYPE_REG && a.Reg == ppc64.REGZERO
}

func regtyp(a *obj.Addr) bool {
	// TODO(rsc): Floating point register exclusions?
	return a.Type == obj.TYPE_REG && ppc64.REG_R0 <= a.Reg && a.Reg <= ppc64.REG_F31 && a.Reg != ppc64.REGZERO
}

/*
 * 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.  This returns 1 if it modified any instructions.
 */
func subprop(r0 *gc.Flow) bool {
	p := r0.Prog
	v1 := &p.From
	if !regtyp(v1) {
		return false
	}
	v2 := &p.To
	if !regtyp(v2) {
		return false
	}
	for r := gc.Uniqp(r0); r != nil; r = gc.Uniqp(r) {
		if gc.Uniqs(r) == nil {
			break
		}
		p = r.Prog
		if p.As == obj.AVARDEF || p.As == obj.AVARKILL {
			continue
		}
		if p.Info.Flags&gc.Call != 0 {
			return false
		}

		if p.Info.Flags&(gc.RightRead|gc.RightWrite) == gc.RightWrite {
			if p.To.Type == v1.Type {
				if p.To.Reg == v1.Reg {
					copysub(&p.To, v1, v2, true)
					if gc.Debug['P'] != 0 {
						fmt.Printf("gotit: %v->%v\n%v", gc.Ctxt.Dconv(v1), gc.Ctxt.Dconv(v2), r.Prog)
						if p.From.Type == v2.Type {
							fmt.Printf(" excise")
						}
						fmt.Printf("\n")
					}

					for r = gc.Uniqs(r); r != r0; r = gc.Uniqs(r) {
						p = r.Prog
						copysub(&p.From, v1, v2, true)
						copysub1(p, v1, v2, true)
						copysub(&p.To, v1, v2, true)
						if gc.Debug['P'] != 0 {
							fmt.Printf("%v\n", r.Prog)
						}
					}

					v1.Reg, v2.Reg = v2.Reg, v1.Reg
					if gc.Debug['P'] != 0 {
						fmt.Printf("%v last\n", r.Prog)
					}
					return true
				}
			}
		}

		if copyau(&p.From, v2) || copyau1(p, v2) || copyau(&p.To, v2) {
			break
		}
		if copysub(&p.From, v1, v2, false) || copysub1(p, v1, v2, false) || copysub(&p.To, v1, v2, false) {
			break
		}
	}

	return false
}

/*
 * 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(r0 *gc.Flow) bool {
	p := r0.Prog
	v1 := &p.From
	v2 := &p.To
	if copyas(v1, v2) {
		if gc.Debug['P'] != 0 {
			fmt.Printf("eliminating self-move: %v\n", r0.Prog)
		}
		return true
	}

	gactive++
	if gc.Debug['P'] != 0 {
		fmt.Printf("trying to eliminate %v->%v move from:\n%v\n", gc.Ctxt.Dconv(v1), gc.Ctxt.Dconv(v2), r0.Prog)
	}
	return copy1(v1, v2, r0.S1, false)
}

// copy1 replaces uses of v2 with v1 starting at r and returns 1 if
// all uses were rewritten.
func copy1(v1 *obj.Addr, v2 *obj.Addr, r *gc.Flow, f bool) bool {
	if uint32(r.Active) == gactive {
		if gc.Debug['P'] != 0 {
			fmt.Printf("act set; return 1\n")
		}
		return true
	}

	r.Active = int32(gactive)
	if gc.Debug['P'] != 0 {
		fmt.Printf("copy1 replace %v with %v f=%v\n", gc.Ctxt.Dconv(v2), gc.Ctxt.Dconv(v1), f)
	}
	for ; r != nil; r = r.S1 {
		p := r.Prog
		if gc.Debug['P'] != 0 {
			fmt.Printf("%v", p)
		}
		if !f && gc.Uniqp(r) == nil {
			// Multiple predecessors; conservatively
			// assume v1 was set on other path
			f = true

			if gc.Debug['P'] != 0 {
				fmt.Printf("; merge; f=%v", f)
			}
		}

		switch t := copyu(p, v2, nil); t {
		case 2: /* rar, can't split */
			if gc.Debug['P'] != 0 {
				fmt.Printf("; %v rar; return 0\n", gc.Ctxt.Dconv(v2))
			}
			return false

		case 3: /* set */
			if gc.Debug['P'] != 0 {
				fmt.Printf("; %v set; return 1\n", gc.Ctxt.Dconv(v2))
			}
			return true

		case 1, /* used, substitute */
			4: /* use and set */
			if f {
				if gc.Debug['P'] == 0 {
					return false
				}
				if t == 4 {
					fmt.Printf("; %v used+set and f=%v; return 0\n", gc.Ctxt.Dconv(v2), f)
				} else {
					fmt.Printf("; %v used and f=%v; return 0\n", gc.Ctxt.Dconv(v2), f)
				}
				return false
			}

			if copyu(p, v2, v1) != 0 {
				if gc.Debug['P'] != 0 {
					fmt.Printf("; sub fail; return 0\n")
				}
				return false
			}

			if gc.Debug['P'] != 0 {
				fmt.Printf("; sub %v->%v\n => %v", gc.Ctxt.Dconv(v2), gc.Ctxt.Dconv(v1), p)
			}
			if t == 4 {
				if gc.Debug['P'] != 0 {
					fmt.Printf("; %v used+set; return 1\n", gc.Ctxt.Dconv(v2))
				}
				return true
			}
		}

		if !f {
			t := copyu(p, v1, nil)
			if t == 2 || t == 3 || t == 4 {
				f = true
				if gc.Debug['P'] != 0 {
					fmt.Printf("; %v set and !f; f=%v", gc.Ctxt.Dconv(v1), f)
				}
			}
		}

		if gc.Debug['P'] != 0 {
			fmt.Printf("\n")
		}
		if r.S2 != nil {
			if !copy1(v1, v2, r.S2, f) {
				return false
			}
		}
	}

	return true
}

// If s==nil, copyu returns the set/use of v in p; otherwise, it
// modifies p to replace reads of v with reads of s and returns 0 for
// success or non-zero for failure.
//
// If s==nil, copy returns one of the following values:
// 	1 if v only used
//	2 if v is set and used in one address (read-alter-rewrite;
// 	  can't substitute)
//	3 if v is only set
//	4 if v is set in one address and used in another (so addresses
// 	  can be rewritten independently)
//	0 otherwise (not touched)
func copyu(p *obj.Prog, v *obj.Addr, s *obj.Addr) int {
	if p.From3Type() != obj.TYPE_NONE {
		// 9g never generates a from3
		fmt.Printf("copyu: from3 (%v) not implemented\n", gc.Ctxt.Dconv(p.From3))
	}

	switch p.As {
	default:
		fmt.Printf("copyu: can't find %v\n", obj.Aconv(p.As))
		return 2

	case obj.ANOP, /* read p->from, write p->to */
		ppc64.AMOVH,
		ppc64.AMOVHZ,
		ppc64.AMOVB,
		ppc64.AMOVBZ,
		ppc64.AMOVW,
		ppc64.AMOVWZ,
		ppc64.AMOVD,
		ppc64.ANEG,
		ppc64.ANEGCC,
		ppc64.AADDME,
		ppc64.AADDMECC,
		ppc64.AADDZE,
		ppc64.AADDZECC,
		ppc64.ASUBME,
		ppc64.ASUBMECC,
		ppc64.ASUBZE,
		ppc64.ASUBZECC,
		ppc64.AFCTIW,
		ppc64.AFCTIWZ,
		ppc64.AFCTID,
		ppc64.AFCTIDZ,
		ppc64.AFCFID,
		ppc64.AFCFIDCC,
		ppc64.AFMOVS,
		ppc64.AFMOVD,
		ppc64.AFRSP,
		ppc64.AFNEG,
		ppc64.AFNEGCC,
		ppc64.AFSQRT:
		if s != nil {
			if copysub(&p.From, v, s, true) {
				return 1
			}

			// Update only indirect uses of v in p->to
			if !copyas(&p.To, v) {
				if copysub(&p.To, v, s, true) {
					return 1
				}
			}
			return 0
		}

		if copyas(&p.To, v) {
			// Fix up implicit from
			if p.From.Type == obj.TYPE_NONE {
				p.From = p.To
			}
			if copyau(&p.From, v) {
				return 4
			}
			return 3
		}

		if copyau(&p.From, v) {
			return 1
		}
		if copyau(&p.To, v) {
			// p->to only indirectly uses v
			return 1
		}

		return 0

	case ppc64.AMOVBU, /* rar p->from, write p->to or read p->from, rar p->to */
		ppc64.AMOVBZU,
		ppc64.AMOVHU,
		ppc64.AMOVHZU,
		ppc64.AMOVWZU,
		ppc64.AMOVDU:
		if p.From.Type == obj.TYPE_MEM {
			if copyas(&p.From, v) {
				// No s!=nil check; need to fail
				// anyway in that case
				return 2
			}

			if s != nil {
				if copysub(&p.To, v, s, true) {
					return 1
				}
				return 0
			}

			if copyas(&p.To, v) {
				return 3
			}
		} else if p.To.Type == obj.TYPE_MEM {
			if copyas(&p.To, v) {
				return 2
			}
			if s != nil {
				if copysub(&p.From, v, s, true) {
					return 1
				}
				return 0
			}

			if copyau(&p.From, v) {
				return 1
			}
		} else {
			fmt.Printf("copyu: bad %v\n", p)
		}

		return 0

	case ppc64.ARLWMI, /* read p->from, read p->reg, rar p->to */
		ppc64.ARLWMICC:
		if copyas(&p.To, v) {
			return 2
		}
		fallthrough

		/* fall through */
	case ppc64.AADD,
		/* read p->from, read p->reg, write p->to */
		ppc64.AADDC,
		ppc64.AADDE,
		ppc64.ASUB,
		ppc64.ASLW,
		ppc64.ASRW,
		ppc64.ASRAW,
		ppc64.ASLD,
		ppc64.ASRD,
		ppc64.ASRAD,
		ppc64.AOR,
		ppc64.AORCC,
		ppc64.AORN,
		ppc64.AORNCC,
		ppc64.AAND,
		ppc64.AANDCC,
		ppc64.AANDN,
		ppc64.AANDNCC,
		ppc64.ANAND,
		ppc64.ANANDCC,
		ppc64.ANOR,
		ppc64.ANORCC,
		ppc64.AXOR,
		ppc64.AMULHW,
		ppc64.AMULHWU,
		ppc64.AMULLW,
		ppc64.AMULLD,
		ppc64.ADIVW,
		ppc64.ADIVD,
		ppc64.ADIVWU,
		ppc64.ADIVDU,
		ppc64.AREM,
		ppc64.AREMU,
		ppc64.AREMD,
		ppc64.AREMDU,
		ppc64.ARLWNM,
		ppc64.ARLWNMCC,
		ppc64.AFADDS,
		ppc64.AFADD,
		ppc64.AFSUBS,
		ppc64.AFSUB,
		ppc64.AFMULS,
		ppc64.AFMUL,
		ppc64.AFDIVS,
		ppc64.AFDIV:
		if s != nil {
			if copysub(&p.From, v, s, true) {
				return 1
			}
			if copysub1(p, v, s, true) {
				return 1
			}

			// Update only indirect uses of v in p->to
			if !copyas(&p.To, v) {
				if copysub(&p.To, v, s, true) {
					return 1
				}
			}
			return 0
		}

		if copyas(&p.To, v) {
			if p.Reg == 0 {
				// Fix up implicit reg (e.g., ADD
				// R3,R4 -> ADD R3,R4,R4) so we can
				// update reg and to separately.
				p.Reg = p.To.Reg
			}

			if copyau(&p.From, v) {
				return 4
			}
			if copyau1(p, v) {
				return 4
			}
			return 3
		}

		if copyau(&p.From, v) {
			return 1
		}
		if copyau1(p, v) {
			return 1
		}
		if copyau(&p.To, v) {
			return 1
		}
		return 0

	case ppc64.ABEQ,
		ppc64.ABGT,
		ppc64.ABGE,
		ppc64.ABLT,
		ppc64.ABLE,
		ppc64.ABNE,
		ppc64.ABVC,
		ppc64.ABVS:
		return 0

	case obj.ACHECKNIL, /* read p->from */
		ppc64.ACMP, /* read p->from, read p->to */
		ppc64.ACMPU,
		ppc64.ACMPW,
		ppc64.ACMPWU,
		ppc64.AFCMPO,
		ppc64.AFCMPU:
		if s != nil {
			if copysub(&p.From, v, s, true) {
				return 1
			}
			if copysub(&p.To, v, s, true) {
				return 1
			}
			return 0
		}

		if copyau(&p.From, v) {
			return 1
		}
		if copyau(&p.To, v) {
			return 1
		}
		return 0

		// 9g never generates a branch to a GPR (this isn't
	// even a normal instruction; liblink turns it in to a
	// mov and a branch).
	case ppc64.ABR: /* read p->to */
		if s != nil {
			if copysub(&p.To, v, s, true) {
				return 1
			}
			return 0
		}

		if copyau(&p.To, v) {
			return 1
		}
		return 0

	case obj.ARET: /* funny */
		if s != nil {
			return 0
		}

		// All registers die at this point, so claim
		// everything is set (and not used).
		return 3

	case ppc64.ABL: /* funny */
		if v.Type == obj.TYPE_REG {
			// TODO(rsc): REG_R0 and REG_F0 used to be
			// (when register numbers started at 0) exregoffset and exfregoffset,
			// which are unset entirely.
			// It's strange that this handles R0 and F0 differently from the other
			// registers. Possible failure to optimize?
			if ppc64.REG_R0 < v.Reg && v.Reg <= ppc64.REGEXT {
				return 2
			}
			if v.Reg == ppc64.REGARG {
				return 2
			}
			if ppc64.REG_F0 < v.Reg && v.Reg <= ppc64.FREGEXT {
				return 2
			}
		}

		if p.From.Type == obj.TYPE_REG && v.Type == obj.TYPE_REG && p.From.Reg == v.Reg {
			return 2
		}

		if s != nil {
			if copysub(&p.To, v, s, true) {
				return 1
			}
			return 0
		}
		if copyau(&p.To, v) {
			return 4
		}
		return 3

		// R0 is zero, used by DUFFZERO, cannot be substituted.
	// R3 is ptr to memory, used and set, cannot be substituted.
	case obj.ADUFFZERO:
		if v.Type == obj.TYPE_REG {
			if v.Reg == 0 {
				return 1
			}
			if v.Reg == 3 {
				return 2
			}
		}

		return 0

		// R3, R4 are ptr to src, dst, used and set, cannot be substituted.
	// R5 is scratch, set by DUFFCOPY, cannot be substituted.
	case obj.ADUFFCOPY:
		if v.Type == obj.TYPE_REG {
			if v.Reg == 3 || v.Reg == 4 {
				return 2
			}
			if v.Reg == 5 {
				return 3
			}
		}

		return 0

	case obj.ATEXT: /* funny */
		if v.Type == obj.TYPE_REG {
			if v.Reg == ppc64.REGARG {
				return 3
			}
		}
		return 0

	case obj.APCDATA,
		obj.AFUNCDATA,
		obj.AVARDEF,
		obj.AVARKILL,
		obj.AVARLIVE,
		obj.AUSEFIELD:
		return 0
	}
}

// copyas returns true if a and v address the same register.
//
// If a is the from operand, this means this operation reads the
// register in v. If a is the to operand, this means this operation
// writes the register in v.
func copyas(a *obj.Addr, v *obj.Addr) bool {
	return regtyp(v) && a.Type == v.Type && a.Reg == v.Reg
}

// copyau returns true if a either directly or indirectly addresses the
// same register as v.
//
// If a is the from operand, this means this operation reads the
// register in v. If a is the to operand, this means the operation
// either reads or writes the register in v (if !copyas(a, v), then
// the operation reads the register in v).
func copyau(a *obj.Addr, v *obj.Addr) bool {
	if copyas(a, v) {
		return true
	}
	if v.Type == obj.TYPE_REG {
		if a.Type == obj.TYPE_MEM || (a.Type == obj.TYPE_ADDR && a.Reg != 0) {
			if v.Reg == a.Reg {
				return true
			}
		}
	}
	return false
}

// copyau1 returns true if p->reg references the same register as v and v
// is a direct reference.
func copyau1(p *obj.Prog, v *obj.Addr) bool {
	return regtyp(v) && v.Reg != 0 && p.Reg == v.Reg
}

// copysub replaces v with s in a if f==true or indicates it if could if f==false.
// Returns true on failure to substitute (it always succeeds on ppc64).
// TODO(dfc) remove unused return value and callers where f=false.
func copysub(a *obj.Addr, v *obj.Addr, s *obj.Addr, f bool) bool {
	if f && copyau(a, v) {
		a.Reg = s.Reg
	}
	return false
}

// copysub1 replaces v with s in p1->reg if f==true or indicates if it could if f==false.
// Returns true on failure to substitute (it always succeeds on ppc64).
// TODO(dfc) remove unused return value and callers where f=false.
func copysub1(p1 *obj.Prog, v *obj.Addr, s *obj.Addr, f bool) bool {
	if f && copyau1(p1, v) {
		p1.Reg = s.Reg
	}
	return false
}

func sameaddr(a *obj.Addr, v *obj.Addr) bool {
	if a.Type != v.Type {
		return false
	}
	if regtyp(v) && a.Reg == v.Reg {
		return true
	}
	if v.Type == obj.NAME_AUTO || v.Type == obj.NAME_PARAM {
		if v.Offset == a.Offset {
			return true
		}
	}
	return false
}

func smallindir(a *obj.Addr, reg *obj.Addr) bool {
	return reg.Type == obj.TYPE_REG && a.Type == obj.TYPE_MEM && a.Reg == reg.Reg && 0 <= a.Offset && a.Offset < 4096
}

func stackaddr(a *obj.Addr) bool {
	return a.Type == obj.TYPE_REG && a.Reg == ppc64.REGSP
}