Ejemplo n.º 1
0
// 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 {
		// 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 */
		mips.AMOVV,
		mips.AMOVF,
		mips.AMOVD,
		mips.AMOVH,
		mips.AMOVHU,
		mips.AMOVB,
		mips.AMOVBU,
		mips.AMOVW,
		mips.AMOVWU,
		mips.AMOVFD,
		mips.AMOVDF,
		mips.AMOVDW,
		mips.AMOVWD,
		mips.AMOVFW,
		mips.AMOVWF,
		mips.AMOVDV,
		mips.AMOVVD,
		mips.AMOVFV,
		mips.AMOVVF,
		mips.ATRUNCFV,
		mips.ATRUNCDV,
		mips.ATRUNCFW,
		mips.ATRUNCDW:
		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 mips.ASGT, /* read p->from, read p->reg, write p->to */
		mips.ASGTU,

		mips.AADD,
		mips.AADDU,
		mips.ASUB,
		mips.ASUBU,
		mips.ASLL,
		mips.ASRL,
		mips.ASRA,
		mips.AOR,
		mips.ANOR,
		mips.AAND,
		mips.AXOR,

		mips.AADDV,
		mips.AADDVU,
		mips.ASUBV,
		mips.ASUBVU,
		mips.ASLLV,
		mips.ASRLV,
		mips.ASRAV,

		mips.AADDF,
		mips.AADDD,
		mips.ASUBF,
		mips.ASUBD,
		mips.AMULF,
		mips.AMULD,
		mips.ADIVF,
		mips.ADIVD:
		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 obj.ACHECKNIL, /* read p->from */
		mips.ABEQ, /* read p->from, read p->reg */
		mips.ABNE,
		mips.ABGTZ,
		mips.ABGEZ,
		mips.ABLTZ,
		mips.ABLEZ,

		mips.ACMPEQD,
		mips.ACMPEQF,
		mips.ACMPGED,
		mips.ACMPGEF,
		mips.ACMPGTD,
		mips.ACMPGTF,
		mips.ABFPF,
		mips.ABFPT,

		mips.AMUL,
		mips.AMULU,
		mips.ADIV,
		mips.ADIVU,
		mips.AMULV,
		mips.AMULVU,
		mips.ADIVV,
		mips.ADIVVU:
		if s != nil {
			if copysub(&p.From, v, s, true) {
				return 1
			}
			if copysub1(p, v, s, true) {
				return 1
			}
			return 0
		}

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

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

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

	case mips.AJAL: /* 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 mips.REG_R0 < v.Reg && v.Reg <= mips.REG_R31 {
				return 2
			}
			if v.Reg == mips.REGARG {
				return 2
			}
			if mips.REG_F0 < v.Reg && v.Reg <= mips.REG_F31 {
				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.
	// R1 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 == 1 {
				return 2
			}
		}

		return 0

	// R1, R2 are ptr to src, dst, used and set, cannot be substituted.
	// R3 is scratch, set by DUFFCOPY, cannot be substituted.
	case obj.ADUFFCOPY:
		if v.Type == obj.TYPE_REG {
			if v.Reg == 1 || v.Reg == 2 {
				return 2
			}
			if v.Reg == 3 {
				return 3
			}
		}

		return 0

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

	case obj.APCDATA,
		obj.AFUNCDATA,
		obj.AVARDEF,
		obj.AVARKILL,
		obj.AVARLIVE,
		obj.AUSEFIELD:
		return 0
	}
}
Ejemplo n.º 2
0
// 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 {
		// 7g never generates a from3
		fmt.Printf("copyu: from3 (%v) not implemented\n", gc.Ctxt.Dconv(p.From3))
	}
	if p.RegTo2 != obj.REG_NONE {
		// 7g never generates a to2
		fmt.Printf("copyu: RegTo2 (%v) not implemented\n", obj.Rconv(int(p.RegTo2)))
	}

	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 */
		arm64.ANEG,
		arm64.AFNEGD,
		arm64.AFNEGS,
		arm64.AFSQRTD,
		arm64.AFCVTZSD,
		arm64.AFCVTZSS,
		arm64.AFCVTZSDW,
		arm64.AFCVTZSSW,
		arm64.AFCVTZUD,
		arm64.AFCVTZUS,
		arm64.AFCVTZUDW,
		arm64.AFCVTZUSW,
		arm64.AFCVTSD,
		arm64.AFCVTDS,
		arm64.ASCVTFD,
		arm64.ASCVTFS,
		arm64.ASCVTFWD,
		arm64.ASCVTFWS,
		arm64.AUCVTFD,
		arm64.AUCVTFS,
		arm64.AUCVTFWD,
		arm64.AUCVTFWS,
		arm64.AMOVB,
		arm64.AMOVBU,
		arm64.AMOVH,
		arm64.AMOVHU,
		arm64.AMOVW,
		arm64.AMOVWU,
		arm64.AMOVD,
		arm64.AFMOVS,
		arm64.AFMOVD:
		if p.Scond == 0 {
			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
		}

		/* rar p->from, write p->to or read p->from, rar p->to */
		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 arm64.AADD, /* read p->from, read p->reg, write p->to */
		arm64.AADDS,
		arm64.ASUB,
		arm64.AADC,
		arm64.AAND,
		arm64.AORR,
		arm64.AEOR,
		arm64.AROR,
		arm64.AMUL,
		arm64.ASMULL,
		arm64.AUMULL,
		arm64.ASMULH,
		arm64.AUMULH,
		arm64.ASDIV,
		arm64.AUDIV,
		arm64.ALSL,
		arm64.ALSR,
		arm64.AASR,
		arm64.AFADDD,
		arm64.AFADDS,
		arm64.AFSUBD,
		arm64.AFSUBS,
		arm64.AFMULD,
		arm64.AFMULS,
		arm64.AFDIVD,
		arm64.AFDIVS:
		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 arm64.ABEQ,
		arm64.ABNE,
		arm64.ABGE,
		arm64.ABLT,
		arm64.ABGT,
		arm64.ABLE,
		arm64.ABLO,
		arm64.ABLS,
		arm64.ABHI,
		arm64.ABHS:
		return 0

	case obj.ACHECKNIL, /* read p->from */
		arm64.ACMP, /* read p->from, read p->reg */
		arm64.AFCMPD,
		arm64.AFCMPS:
		if s != nil {
			if copysub(&p.From, v, s, true) {
				return 1
			}
			if copysub1(p, v, s, true) {
				return 1
			}
			return 0
		}

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

	case arm64.AB: /* 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 arm64.ABL: /* funny */
		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

	// R31 is zero, used by DUFFZERO, cannot be substituted.
	// R16 is ptr to memory, used and set, cannot be substituted.
	case obj.ADUFFZERO:
		if v.Type == obj.TYPE_REG {
			if v.Reg == 31 {
				return 1
			}
			if v.Reg == 16 {
				return 2
			}
		}

		return 0

	// R16, R17 are ptr to src, dst, used and set, cannot be substituted.
	// R27 is scratch, set by DUFFCOPY, cannot be substituted.
	case obj.ADUFFCOPY:
		if v.Type == obj.TYPE_REG {
			if v.Reg == 16 || v.Reg == 17 {
				return 2
			}
			if v.Reg == 27 {
				return 3
			}
		}

		return 0

	case arm64.AHINT,
		obj.ATEXT,
		obj.APCDATA,
		obj.AFUNCDATA,
		obj.AVARDEF,
		obj.AVARKILL,
		obj.AVARLIVE,
		obj.AUSEFIELD:
		return 0
	}
}
Ejemplo n.º 3
0
// 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.AFCFIDU,
		ppc64.AFCFIDUCC,
		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
	}
}
Ejemplo n.º 4
0
// 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:
// 	_Read           if v only used
//	_ReadWriteSame  if v is set and used in one address (read-alter-rewrite;
// 	                can't substitute)
//	_Write          if v is only set
//	_ReadWriteDiff  if v is set in one address and used in another (so addresses
// 	                can be rewritten independently)
//	_None           otherwise (not touched)
func copyu(p *obj.Prog, v *obj.Addr, s *obj.Addr) usage {
	if p.From3Type() != obj.TYPE_NONE && p.From3Type() != obj.TYPE_CONST {
		// Currently we never generate a From3 with anything other than a constant in it.
		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 _ReadWriteSame

	case // read p.From, write p.To
		s390x.AMOVH,
		s390x.AMOVHZ,
		s390x.AMOVB,
		s390x.AMOVBZ,
		s390x.AMOVW,
		s390x.AMOVWZ,
		s390x.AMOVD,
		s390x.ANEG,
		s390x.AADDME,
		s390x.AADDZE,
		s390x.ASUBME,
		s390x.ASUBZE,
		s390x.AFMOVS,
		s390x.AFMOVD,
		s390x.ALEDBR,
		s390x.AFNEG,
		s390x.ALDEBR,
		s390x.ACLFEBR,
		s390x.ACLGEBR,
		s390x.ACLFDBR,
		s390x.ACLGDBR,
		s390x.ACFEBRA,
		s390x.ACGEBRA,
		s390x.ACFDBRA,
		s390x.ACGDBRA,
		s390x.ACELFBR,
		s390x.ACELGBR,
		s390x.ACDLFBR,
		s390x.ACDLGBR,
		s390x.ACEFBRA,
		s390x.ACEGBRA,
		s390x.ACDFBRA,
		s390x.ACDGBRA,
		s390x.AFSQRT:

		if s != nil {
			copysub(&p.From, v, s)

			// Update only indirect uses of v in p.To
			if !copyas(&p.To, v) {
				copysub(&p.To, v, s)
			}
			return _None
		}

		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 _ReadWriteDiff
			}
			return _Write
		}

		if copyau(&p.From, v) {
			return _Read
		}
		if copyau(&p.To, v) {
			// p.To only indirectly uses v
			return _Read
		}

		return _None

	// read p.From, read p.Reg, write p.To
	case s390x.AADD,
		s390x.AADDC,
		s390x.AADDE,
		s390x.ASUB,
		s390x.ASLW,
		s390x.ASRW,
		s390x.ASRAW,
		s390x.ASLD,
		s390x.ASRD,
		s390x.ASRAD,
		s390x.ARLL,
		s390x.ARLLG,
		s390x.AOR,
		s390x.AORN,
		s390x.AAND,
		s390x.AANDN,
		s390x.ANAND,
		s390x.ANOR,
		s390x.AXOR,
		s390x.AMULLW,
		s390x.AMULLD,
		s390x.AMULHD,
		s390x.AMULHDU,
		s390x.ADIVW,
		s390x.ADIVD,
		s390x.ADIVWU,
		s390x.ADIVDU,
		s390x.AFADDS,
		s390x.AFADD,
		s390x.AFSUBS,
		s390x.AFSUB,
		s390x.AFMULS,
		s390x.AFMUL,
		s390x.AFDIVS,
		s390x.AFDIV:
		if s != nil {
			copysub(&p.From, v, s)
			copysub1(p, v, s)

			// Update only indirect uses of v in p.To
			if !copyas(&p.To, v) {
				copysub(&p.To, v, s)
			}
		}

		if copyas(&p.To, v) {
			if p.Reg == 0 {
				p.Reg = p.To.Reg
			}
			if copyau(&p.From, v) || copyau1(p, v) {
				return _ReadWriteDiff
			}
			return _Write
		}

		if copyau(&p.From, v) {
			return _Read
		}
		if copyau1(p, v) {
			return _Read
		}
		if copyau(&p.To, v) {
			return _Read
		}
		return _None

	case s390x.ABEQ,
		s390x.ABGT,
		s390x.ABGE,
		s390x.ABLT,
		s390x.ABLE,
		s390x.ABNE,
		s390x.ABVC,
		s390x.ABVS:
		return _None

	case obj.ACHECKNIL, // read p.From
		s390x.ACMP, // read p.From, read p.To
		s390x.ACMPU,
		s390x.ACMPW,
		s390x.ACMPWU,
		s390x.AFCMPO,
		s390x.AFCMPU,
		s390x.ACEBR,
		s390x.AMVC,
		s390x.ACLC,
		s390x.AXC,
		s390x.AOC,
		s390x.ANC:
		if s != nil {
			copysub(&p.From, v, s)
			copysub(&p.To, v, s)
			return _None
		}

		if copyau(&p.From, v) {
			return _Read
		}
		if copyau(&p.To, v) {
			return _Read
		}
		return _None

	case s390x.ACMPBNE, s390x.ACMPBEQ,
		s390x.ACMPBLT, s390x.ACMPBLE,
		s390x.ACMPBGT, s390x.ACMPBGE,
		s390x.ACMPUBNE, s390x.ACMPUBEQ,
		s390x.ACMPUBLT, s390x.ACMPUBLE,
		s390x.ACMPUBGT, s390x.ACMPUBGE:
		if s != nil {
			copysub(&p.From, v, s)
			copysub1(p, v, s)
			return _None
		}
		if copyau(&p.From, v) {
			return _Read
		}
		if copyau1(p, v) {
			return _Read
		}
		return _None

	case s390x.ACLEAR:
		if s != nil {
			copysub(&p.To, v, s)
			return _None
		}
		if copyau(&p.To, v) {
			return _Read
		}
		return _None

	// go never generates a branch to a GPR
	// read p.To
	case s390x.ABR:
		if s != nil {
			copysub(&p.To, v, s)
			return _None
		}

		if copyau(&p.To, v) {
			return _Read
		}
		return _None

	case obj.ARET, obj.AUNDEF:
		if s != nil {
			return _None
		}

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

	case s390x.ABL:
		if v.Type == obj.TYPE_REG {
			if s390x.REGARG != -1 && v.Reg == s390x.REGARG {
				return _ReadWriteSame
			}
			if p.From.Type == obj.TYPE_REG && p.From.Reg == v.Reg {
				return _ReadWriteSame
			}
			if v.Reg == s390x.REGZERO {
				// Deliberately inserted nops set R0.
				return _ReadWriteSame
			}
			if v.Reg == s390x.REGCTXT {
				// Context register for closures.
				// TODO(mundaym): not sure if we need to exclude this.
				return _ReadWriteSame
			}
		}
		if s != nil {
			copysub(&p.To, v, s)
			return _None
		}
		if copyau(&p.To, v) {
			return _ReadWriteDiff
		}
		return _Write

	case obj.ATEXT:
		if v.Type == obj.TYPE_REG {
			if v.Reg == s390x.REGARG {
				return _Write
			}
		}
		return _None

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