shithub: riscv

ref: 9ced712a2ad70557a8ceb89ff3b969b92c85f68c
dir: /sys/src/cmd/7c/peep.c/

#include "gc.h"

int xtramodes(Reg*, Adr*);

Reg* findset(Reg *r, Adr *v);
Reg* findpre(Reg *r, Adr *v);
Reg* findinc(Reg *r, Reg *r2, Adr *v);
static void
storeprop(int as, Adr *a, Adr *v, Reg *r);

static void
swapprog(Prog *p1, Prog *p2)
{
	Prog tmp = *p1;

	p1->as = p2->as;
	p1->scond = p2->scond;
	p1->from = p2->from;
	p1->to = p2->to;
	p1->reg = p2->reg;

	p2->as = tmp.as;
	p2->scond = tmp.scond;
	p2->from = tmp.from;
	p2->to = tmp.to;
	p2->reg = tmp.reg;
}

static int
isu32op(Prog *p)
{
	switch(p->as){
	case AADCSW:
	case AADCW:
	case AADDSW:
	case AADDW:
	case AANDSW:
	case AANDW:
	case AASRW:
	case ABFIW:
	case ABFMW:
	case ABFXILW:
	case ABICSW:
	case ABICW:
	case ACBNZW:
	case ACBZW:
	case ACCMNW:
	case ACCMPW:
	case ACINCW:
	case ACINVW:
	case ACLSW:
	case ACLZW:
	case ACMNW:
	case ACNEGW:
	case ACRC32CW:
	case ACRC32W:
	case ACSELW:
	case ACSETMW:
	case ACSETW:
	case ACSINCW:
	case ACSINVW:
	case ACSNEGW:
	case AEONW:
	case AEORW:
	case AEXTRW:
	case ALDARW:
	case ALDAXPW:
	case ALDAXRW:
	case ALDXRW:
	case ALDXPW:
	case ALSLW:
	case ALSRW:
	case AMADDW:
	case AMNEGW:
	case AMOVKW:
	case AMOVNW:
	case AMOVZW:
	case AMSUBW:
	case AMULW:
	case AMVNW:
	case ANEGSW:
	case ANEGW:
	case ANGCSW:
	case ANGCW:
	case AORNW:
	case AORRW:
	case ARBITW:
	case AREMW:
	case AREV16W:
	case AREVW:
	case ARORW:
	case ASBCSW:
	case ASBCW:
	case ASBFIZW:
	case ASBFMW:
	case ASBFXW:
	case ASDIVW:
	case ASTXPW:
	case ASTXRW:
	case ASTLRW:
	case ASTLXPW:
	case ASTLXRW:
	case ASUBSW:
	case ASUBW:
	case ASXTBW:
	case ASXTHW:
	case ATSTW:
	case AUBFIZW:
	case AUBFMW:
	case AUBFXW:
	case AUDIVW:
	case AUREMW:
	case AUMULL:
	case AUXTW:
	case AUXTBW:
	case AUXTHW:
	case AMOVWU:
		return 1;
	}
	return 0;
}

static int
independent(Prog *p1, Prog *p2)
{
	switch(p1->as){
	case ACMP:
	case ACMPW:
	case AFCMPS:
	case AFCMPD:
	case ACBZ:
	case ACBZW:
	case ACBNZ:
	case ACBNZW:
	case ATBZ:
	case ATBNZ:

	case AB:
	case ABL:
	case ARET:
	case ARETURN:
		return 0;
	}

	if(regtyp(&p1->to)){
		if(!copyu(p2, &p1->to, A))
			return 1;
		return 0;
	}

	if(p2->from.type == D_CONST || p2->from.type == D_FCONST)
		return 1;

	if(p1->to.type == D_OREG){
		int w;

		if(p2->from.type != D_OREG)
			return 1;

		switch(p1->as){
		default:
			return 0;
		case AMOV:
		case AFMOVD:
			w = 8;
			break;
		case AMOVW:
		case AMOVWU:
		case AFMOVS:
			w = 4;
			break;
		case AMOVH:
		case AMOVHU:
			w = 2;
			break;
		case AMOVB:
		case AMOVBU:
			w = 1;
			break;
		}

		if(p1->to.reg != REGSP && p1->to.name <= D_NONE)
			return 0;
		if(p2->from.reg != REGSP && p2->from.name <= D_NONE)
			return 0;

		if(p1->to.name != p2->from.name
		|| p1->to.reg != p2->from.reg
		|| abs(p1->to.offset - p2->from.offset) >= w)
			return 1;
	}

	/* assume not independent */
	return 0;
}

void
peep(void)
{
	Reg *r, *r1, *r2;
	Prog *p, *p1;
	int t;
/*
 * complete R structure
 */
	t = 0;
	for(r=firstr; r!=R; r=r1) {
		r1 = r->link;
		if(r1 == R)
			break;
		p = r->prog->link;
		while(p != r1->prog)
		switch(p->as) {
		default:
			r2 = rega();
			r->link = r2;
			r2->link = r1;

			r2->prog = p;
			r2->p1 = r;
			r->s1 = r2;
			r2->s1 = r1;
			r1->p1 = r2;

			r = r2;
			t++;

		case ADATA:
		case AGLOBL:
		case ANAME:
		case ASIGNAME:
			p = p->link;
		}
	}

loop1:
	t = 0;
	for(r=firstr; r!=R; r=r->link) {
		p = r->prog;

		/* registerize variable loads following stores */
		if(p->as == AMOV || p->as == AMOVW || p->as == AMOVWU || p->as == AFMOVS || p->as == AFMOVD){
			if(p->from.type == D_REG && p->to.type == D_OREG && p->to.name > D_NONE)
				storeprop(p->as, &p->from, &p->to, r->s1);
		}

		if(p->as == ALSL || p->as == ALSR || p->as == AASR
		|| p->as == ALSLW || p->as == ALSRW || p->as == AASRW) {
			/*
			 * elide shift into D_SHIFT operand of subsequent instruction
			 */
			if(0 && shiftprop(r)) {
				excise(r);
				t++;
			}
		} else
		if(p->as == ASXTW && p->from.type == D_REG && p->to.type == D_REG){
			if((r1 = findset(r, &p->from)) != R){
				p1 = r1->prog;
				switch(p1->as){
				case AMOVW:
					/* MOVW $const,r; does not sign extend */
					if(p1->from.type == D_CONST && (p1->from.offset & 0x80000000) != 0)
						break;
				case AMOVB:
				case AMOVH:
				case AMOVBU:
				case AMOVHU:
					if(p1->to.type == p->from.type && p1->to.reg == p->from.reg)
						p->as = AMOVW;
					break;
				}
			}
		} else
		if((p->as == AMOVB || p->as == AMOVBU || p->as == AMOVH || p->as == AMOVHU || p->as == AMOVWU)
		&& (p->from.type == D_REG && p->to.type == D_REG)){
			if((r1 = findset(r, &p->from)) != R){
				p1 = r1->prog;
				if(p1->to.type == p->from.type && p1->to.reg == p->from.reg){
					if(p1->as == p->as || p->as == AMOVWU && isu32op(p1))
						p->as = AMOVW;
				}
			}
		}

		if(p->as == AMOV || p->as == AMOVW || p->as == AFMOVS || p->as == AFMOVD)
		if(regtyp(&p->to)) {
			if(p->from.type == D_CONST || p->from.type == D_FCONST)
				constprop(p->as, &p->from, &p->to, r->s1);
			else 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++;
				}
			}
			if(regzer(&p->from))
			if(p->to.type == D_REG) {
				p->from.type = D_REG;
				p->from.reg = REGZERO;
				if(copyprop(r)) {
					excise(r);
					t++;
				} else
				if(subprop(r) && copyprop(r)) {
					excise(r);
					t++;
				}
			}
		}
	}
	if(t)
		goto loop1;

	/*
	 * look for MOVB x,R; MOVB R,R
	 */
	for(r=firstr; r!=R; r=r->link) {
		p = r->prog;
		switch(p->as) {
		default:
			continue;
		case AEOR:
			/*
			 * EOR -1,x,y => MVN x,y
			 */
			if(p->from.type == D_CONST && p->from.offset == -1) {
				p->as = AMVN;
				p->from.type = D_REG;
				if(p->reg != NREG)
					p->from.reg = p->reg;
				else
					p->from.reg = p->to.reg;
				p->reg = NREG;
			}
			continue;
		case AEORW:
			/*
			 * EOR -1,x,y => MVN x,y
			 */
			if(p->from.type == D_CONST && (p->from.offset&0xFFFFFFFF)==0xFFFFFFFF){
				p->as = AMVNW;
				p->from.type = D_REG;
				if(p->reg != NREG)
					p->from.reg = p->reg;
				else
					p->from.reg = p->to.reg;
				p->reg = NREG;
			}
			continue;
		case AMOVH:
		case AMOVHU:
		case AMOVB:
		case AMOVBU:
		case AMOVW:
		case AMOVWU:
			if(p->to.type != D_REG)
				continue;
			break;
		}
		r1 = r->link;
		if(r1 == R)
			continue;
		p1 = r1->prog;
		if(p1->as != p->as)
			continue;
		if(p1->from.type != D_REG || p1->from.reg != p->to.reg)
			continue;
		if(p1->to.type != D_REG || p1->to.reg != p->to.reg)
			continue;
		excise(r1);
	}

#ifdef NOTYET
	for(r=firstr; r!=R; r=r->link) {
		p = r->prog;
		switch(p->as) {
		case AMOVW:
		case AMOVB:
		case AMOVBU:
			if(p->from.type == D_OREG && p->from.offset == 0)
				xtramodes(r, &p->from);
			else if(p->to.type == D_OREG && p->to.offset == 0)
				xtramodes(r, &p->to);
			else
				continue;
			break;
		case ACMP:
			/*
			 * elide CMP $0,x if calculation of x can set condition codes
			 */
			if(p->from.type != D_CONST || p->from.offset != 0)
				continue;
			r2 = r->s1;
			if(r2 == R)
				continue;
			t = r2->prog->as;
			switch(t) {
			default:
				continue;
			case ABEQ:
			case ABNE:
			case ABMI:
			case ABPL:
				break;
			case ABGE:
				t = ABPL;
				break;
			case ABLT:
				t = ABMI;
				break;
			case ABHI:
				t = ABNE;
				break;
			case ABLS:
				t = ABEQ;
				break;
			}
			r1 = r;
			do
				r1 = uniqp(r1);
			while (r1 != R && r1->prog->as == ANOP);
			if(r1 == R)
				continue;
			p1 = r1->prog;
			if(p1->to.type != D_REG)
				continue;
			if(p1->to.reg != p->reg)
			if(!(p1->as == AMOVW && p1->from.type == D_REG && p1->from.reg == p->reg))
				continue;
			switch(p1->as) {
			default:
				continue;
			case AMOVW:
				if(p1->from.type != D_REG)
					continue;
			case AAND:
			case AEOR:
			case AORR:
			case ABIC:
			case AMVN:
			case ASUB:
			case AADD:
			case AADC:
			case ASBC:
				break;
			}
			p1->scond |= C_SBIT;
			r2->prog->as = t;
			excise(r);
			continue;
		}
	}
#endif

	/*
	 * software pipeline loads:
	 *
	 * insert a independent instruction (YYY) after a load:
	 * MOV v, r1
	 * XXX r1, x
	 * YYY ... (not reading x or touching r1)
	 * ---
	 * MOV v, r1
	 * YYY ... (not reading x or touching r1)
	 * XXX r1, x
	 */
	for(r=firstr; r!=R; r=r->link) {
		p = r->prog;
		switch(p->as){
		default:
			continue;
		case AFMOVD:
		case AFMOVS:
			if(p->from.type != D_OREG || p->to.type != D_FREG)
				continue;
			break;
		case AMOV:
		case AMOVW:
		case AMOVWU:
		case AMOVH:
		case AMOVHU:
		case AMOVB:
		case AMOVBU:
			if(p->from.type != D_OREG || p->to.type != D_REG)
				continue;
			break;
		}
		for(r1 = uniqs(r); r1 != R && r1->prog->as == ANOP; r1 = uniqs(r1)){
			if(uniqp(r1) == R){
				r1 = R;
				break;
			}
		}
		if(r1 == R || uniqp(r1) == R)
			continue;
		p1 = r1->prog;
		if(!copyu(p1, &p->to, A))
			continue;

		for(r2 = uniqs(r1); r2 != R && r2->prog->as == ANOP; r2 = uniqs(r2)){
			if(uniqp(r2) == R){
				r2 = R;
				break;
			}
		}
		if(r2 == R || uniqp(r2) == R)
			continue;
		if(copyu(r2->prog, &p->to, A))
			continue;

		if(!independent(p1, r2->prog))
			continue;
		if(!independent(r2->prog, p1))
			continue;

		/*
		 * if YYY happens to be a move from v, use register:
		 * MOV v, r1
		 * MOV v, r2
		 * ---
		 * MOV v, r1
		 * MOV r1, r2
		 */
		if(p->as == r2->prog->as
		&& (p->from.reg == REGSP || p->from.name > D_NONE)
		&& copyas(&p->from, &r2->prog->from))
			r2->prog->from = p->to;

		swapprog(p1, r2->prog);
		t++;
	}
	if(t)
		goto loop1;

#ifdef XXX
	predicate();
#endif
}

void
excise(Reg *r)
{
	Prog *p;

	p = r->prog;
	p->as = ANOP;
	p->scond = zprog.scond;
	p->from = zprog.from;
	p->from3 = zprog.from3;
	p->to = zprog.to;
	p->reg = zprog.reg; /**/
}

Reg*
uniqp(Reg *r)
{
	Reg *r1;

	r1 = r->p1;
	if(r1 == R) {
		r1 = r->p2;
		if(r1 == R || r1->p2link != R)
			return R;
	} else
		if(r->p2 != R)
			return R;
	return r1;
}

Reg*
uniqs(Reg *r)
{
	Reg *r1;

	r1 = r->s1;
	if(r1 == R) {
		r1 = r->s2;
		if(r1 == R)
			return R;
	} else
		if(r->s2 != R)
			return R;
	return r1;
}

/*
 * convert references to $0 to references to ZR (REGZERO)
 */
int
regzer(Adr *a)
{
return 0;
	switch(a->type){
	case D_CONST:
		return a->sym == S && a->offset == 0;
	case D_REG:
		return a->reg == REGZERO;
	}
	return 0;
}

int
regtyp(Adr *a)
{

	if(a->type == D_REG){
		if(a->reg == REGZERO)
			return 0;
		return 1;
	}
	if(a->type == D_FREG)
		return 1;
	return 0;
}

/*
 * the idea is to substitute
 * one register for another
 * from one MOV to another
 *	MOV	a, R0
 *	ADD	b, R0	/ no use of R1
 *	MOV	R0, R1
 * would be converted to
 *	MOV	a, R1
 *	ADD	b, R1
 *	MOV	R1, R0
 * hopefully, then the former or latter MOV
 * will be eliminated by copy propagation.
 */
int
subprop(Reg *r0)
{
	Prog *p;
	Adr *v1, *v2;
	Reg *r;
	int t;

	p = r0->prog;
	v1 = &p->from;
	if(!regtyp(v1))
		return 0;
	v2 = &p->to;
	if(!regtyp(v2))
		return 0;
	for(r=uniqp(r0); r!=R; r=uniqp(r)) {
		if(uniqs(r) == R)
			break;
		p = r->prog;
		switch(p->as) {
		case ABL:
			return 0;

		case ACMP:
		case ACMN:
		case AADC:
		case AADCS:
		case AADD:
		case AADDS:
		case ASUB:
		case ASUBS:
		case ALSL:
		case ALSR:
		case AASR:
		case AROR:
		case AORR:
		case AAND:
		case AANDS:
		case AEOR:
		case AMUL:
		case ASDIV:
		case AUDIV:
		case AREM:
		case AUREM:

		case ACMPW:
		case ACMNW:
		case AADCW:
		case AADCSW:
		case AADDSW:
		case AADDW:
		case ASUBSW:
		case ASUBW:
		case ALSLW:
		case ALSRW:
		case AASRW:
		case ARORW:
		case AORRW:
		case AANDW:
		case AANDSW:
		case AEORW:
		case AMULW:
		case ASDIVW:
		case AUDIVW:
		case AREMW:
		case AUREMW:

		case AFCMPS:
		case AFCMPD:
		case AFADDD:
		case AFADDS:
		case AFSUBD:
		case AFSUBS:
		case AFMULD:
		case AFMULS:
		case AFDIVD:
		case AFDIVS:
			if(p->to.type == v1->type)
			if(p->to.reg == v1->reg) {
				if(p->reg == NREG)
					p->reg = p->to.reg;
				goto gotit;
			}
			break;

		case ANEG:
		case ANEGS:
		case ANEGSW:
		case ANEGW:
		case ANGC:
		case ANGCS:
		case ANGCSW:
		case ANGCW:
		case AMVN:
		case AMVNW:
		case AFNEGD:
		case AFNEGS:
		case AFABSS:
		case AFABSD:
		case AFSQRTS:
		case AFSQRTD:
		case AFMOVS:
		case AFMOVD:
		case AMOVB:
		case AMOVBU:
		case AMOVH:
		case AMOVHU:
		case AMOVW:
		case AMOVWU:
		case AMOV:
		case ASXTW:
			if(p->to.type == v1->type)
			if(p->to.reg == v1->reg)
				goto gotit;
			break;

		}
		if(copyau(&p->from, v2) ||
		   copyau1(p, v2) ||
		   copyau(&p->to, v2))
			break;
		if(copysub(&p->from, v1, v2, 0) ||
		   copysub1(p, v1, v2, 0) ||
		   copysub(&p->to, v1, v2, 0))
			break;
	}
	return 0;

gotit:
	copysub(&p->to, v1, v2, 1);
	if(debug['P']) {
		print("gotit: %D->%D\n%P", v1, v2, r->prog);
		if(p->from.type == v2->type)
			print(" excise");
		print("\n");
	}
	for(r=uniqs(r); r!=r0; r=uniqs(r)) {
		p = r->prog;
		copysub(&p->from, v1, v2, 1);
		copysub1(p, v1, v2, 1);
		copysub(&p->to, v1, v2, 1);
		if(debug['P'])
			print("%P\n", r->prog);
	}
	t = v1->reg;
	v1->reg = v2->reg;
	v2->reg = t;
	if(debug['P'])
		print("%P last\n", r->prog);
	return 1;
}

/*
 * 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	F=0
 *	(use v2	s/v2/v1/)*
 *	set v1	F=1
 *	set v2	return success
 */
int
copyprop(Reg *r0)
{
	Prog *p;
	Adr *v1, *v2;
	Reg *r;

	p = r0->prog;
	v1 = &p->from;
	v2 = &p->to;
	if(copyas(v1, v2))
		return 1;
	for(r=firstr; r!=R; r=r->link)
		r->active = 0;
	return copy1(v1, v2, r0->s1, 0);
}

int
copy1(Adr *v1, Adr *v2, Reg *r, int f)
{
	int t;
	Prog *p;

	if(r->active) {
		if(debug['P'])
			print("act set; return 1\n");
		return 1;
	}
	r->active = 1;
	if(debug['P'])
		print("copy %D->%D f=%d\n", v1, v2, f);
	for(; r != R; r = r->s1) {
		p = r->prog;
		if(debug['P'])
			print("%P", p);
		if(!f && uniqp(r) == R) {
			f = 1;
			if(debug['P'])
				print("; merge; f=%d", f);
		}
		t = copyu(p, v2, A);
		switch(t) {
		case 2:	/* rar, cant split */
			if(debug['P'])
				print("; %D rar; return 0\n", v2);
			return 0;

		case 3:	/* set */
			if(debug['P'])
				print("; %D set; return 1\n", v2);
			return 1;

		case 1:	/* used, substitute */
		case 4:	/* use and set */
			if(f) {
				if(!debug['P'])
					return 0;
				if(t == 4)
					print("; %D used+set and f=%d; return 0\n", v2, f);
				else
					print("; %D used and f=%d; return 0\n", v2, f);
				return 0;
			}
			if(copyu(p, v2, v1)) {
				if(debug['P'])
					print("; sub fail; return 0\n");
				return 0;
			}
			if(debug['P'])
				print("; sub%D/%D", v2, v1);
			if(t == 4) {
				if(debug['P'])
					print("; %D used+set; return 1\n", v2);
				return 1;
			}
			break;
		}
		if(!f) {
			t = copyu(p, v1, A);
			if(!f && (t == 2 || t == 3 || t == 4)) {
				f = 1;
				if(debug['P'])
					print("; %D set and !f; f=%d", v1, f);
			}
		}
		if(debug['P'])
			print("\n");
		if(r->s2)
			if(!copy1(v1, v2, r->s2, f))
				return 0;
	}
	return 1;
}

/*
 * 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.
 */
void
constprop(int as, Adr *c1, Adr *v1, Reg *r)
{
	Prog *p;

	/* should be encodable with ZR */
	if(c1->type == D_CONST && c1->sym == S && c1->offset == 0)
		return;

	if(debug['C'])
		print("constprop %D->%D\n", c1, v1);

	for(; r != R; r = r->s1) {
		p = r->prog;
		if(debug['C'])
			print("%P", p);
		if(uniqp(r) == R) {
			if(debug['C'])
				print("; merge; return\n");
			return;
		}
		if((p->as == as || p->as == AMOVW || p->as == AMOVWU
		|| (p->as == AMOV && c1->offset >= 0))	/* immediate loads do not sign extend */
		&& copyas(&p->from, c1)) {
			if(debug['C'])
				print("; sub%D/%D", &p->from, v1);
			p->from = *v1;
		} else if(copyu(p, v1, A) > 1) {
			if(debug['C'])
				print("; %Dset; return\n", v1);
			return;
		}
		if(debug['C'])
			print("\n");
		if(r->s2)
			constprop(as, c1, v1, r->s2);
	}
}

/*
 * Registerize loads from local variables:
 *
 * MOV a, v
 * ... (a and v not touched)
 * MOV v, b
 * ----
 * MOV a, v
 * ... (a and v not touched)
 * MOV a, b
 */
static void
storeprop(int as, Adr *a, Adr *v, Reg *r)
{
	Prog *p;

	for(; r != R; r = r->s1) {
		if(uniqp(r) == R)
			return;

		p = r->prog;
		if((as == p->as
		|| (as == AMOV && (p->as == AMOVW || p->as == AMOVWU))
		|| (as == AMOVW && p->as == AMOVWU)
		|| (as == AMOVWU && p->as == AMOVW))
		&& copyas(&p->from, v)){
			p->from = *a;
			continue;
		}

		if(copyu(p, a, A) > 1)
			return;

		if(p->to.type == D_OREG || p->to.type == D_XPRE || p->to.type == D_XPOST)
			if(p->to.name <= D_NONE || copyas(&p->to, v))
				return;

		if(r->s2)
			storeprop(as, a, v, r->s2);
	}
}

/*
 * ALSL 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
 * ..
 */
#define FAIL(msg) { if(debug['H']) print("\t%s; FAILURE\n", msg); return 0; }
int
shiftprop(Reg *r)
{
	Reg *r1;
	Prog *p, *p1, *p2;
	int n, o;
	Adr a;

	p = r->prog;
	if(p->to.type != D_REG)
		FAIL("BOTCH: result not reg");
	n = p->to.reg;
	a = zprog.from;
	if(p->reg != NREG && p->reg != p->to.reg) {
		a.type = D_REG;
		a.reg = p->reg;
	}
	if(debug['H'])
		print("shiftprop\n%P", p);
	r1 = r;
	for(;;) {
		/* find first use of shift result; abort if shift operands or result are changed */
		r1 = uniqs(r1);
		if(r1 == R)
			FAIL("branch");
		if(uniqp(r1) == R)
			FAIL("merge");
		p1 = r1->prog;
		if(debug['H'])
			print("\n%P", p1);
		switch(copyu(p1, &p->to, A)) {
		case 0:	/* not used or set */
			if((p->from.type == D_REG && copyu(p1, &p->from, A) > 1) ||
			   (a.type == D_REG && copyu(p1, &a, A) > 1))
				FAIL("args modified");
			continue;
		case 3:	/* set, not used */
			FAIL("BOTCH: noref");
		}
		break;
	}
	/* check whether substitution can be done */
	switch(p1->as) {
	case ABIC:
	case ACMP:
	case ACMN:
		if(p1->reg == n)
			FAIL("can't swap");
		if(p1->reg == NREG && p1->to.reg == n)
			FAIL("shift result used twice");
	case AMVN:
		if(p1->from.type == D_SHIFT)
			FAIL("shift result used in shift");
		if(p1->from.type != D_REG || p1->from.reg != n)
			FAIL("BOTCH: where is it used?");
		break;
	}
	/* check whether shift result is used subsequently */
	p2 = p1;
	if(p1->to.reg != n)
	for (;;) {
		r1 = uniqs(r1);
		if(r1 == R)
			FAIL("inconclusive");
		p1 = r1->prog;
		if(debug['H'])
			print("\n%P", p1);
		switch(copyu(p1, &p->to, A)) {
		case 0:	/* not used or set */
			continue;
		case 3: /* set, not used */
			break;
		default:/* used */
			FAIL("reused");
		}
		break;
	}
	/* make the substitution */
	p2->from.type = D_SHIFT;
	p2->from.reg = NREG;
	o = p->reg;
	if(o == NREG)
		o = p->to.reg;
	switch(p->from.type){
	case D_CONST:
		o |= (p->from.offset&0x3f)<<7;
		break;
	case D_REG:
		o |= (1<<4) | (p->from.reg<<8);
		break;
	}
	switch(p->as){
	case ALSL:
		o |= 0<<5;
		break;
	case ALSR:
		o |= 1<<5;
		break;
	case AASR:
		o |= 2<<5;
		break;
	}
	p2->from.offset = o;
	if(debug['H'])
		print("\t=>%P\tSUCCEED\n", p2);
	return 1;
}

Reg*
findset(Reg *r, Adr *v)
{

	Reg *r1;

	for(r1=uniqp(r); r1!=R; r=r1,r1=uniqp(r)) {
		if(uniqs(r1) != r)
			return R;
		if(copyu(r1->prog, v, A) > 1)
			return r1;
	}
	return R;
}

Reg*
findpre(Reg *r, Adr *v)
{
	Reg *r1;

	for(r1=uniqp(r); r1!=R; r=r1,r1=uniqp(r)) {
		if(uniqs(r1) != r)
			return R;
		switch(copyu(r1->prog, v, A)) {
		case 1: /* used */
		case 2: /* read-alter-rewrite */
			return R;
		case 3: /* set */
		case 4: /* set and used */
			return r1;
		}
	}
	return R;
}

Reg*
findinc(Reg *r, Reg *r2, Adr *v)
{
	Reg *r1;
	Prog *p;


	for(r1=uniqs(r); r1!=R && r1!=r2; r=r1,r1=uniqs(r)) {
		if(uniqp(r1) != r)
			return R;
		switch(copyu(r1->prog, v, A)) {
		case 0: /* not touched */
			continue;
		case 4: /* set and used */
			p = r1->prog;
			if(p->as == AADD)
			if(p->from.type == D_CONST)
			if(p->from.offset > -256 && p->from.offset < 256)
				return r1;
		default:
			return R;
		}
	}
	return R;
}

int
nochange(Reg *r, Reg *r2, Prog *p)
{
	Adr a[3];
	int i, n;

	if(r == r2)
		return 1;
	n = 0;
	if(p->reg != NREG && p->reg != p->to.reg) {
		a[n].type = D_REG;
		a[n++].reg = p->reg;
	}
	switch(p->from.type) {
	case D_SHIFT:
		a[n].type = D_REG;
		a[n++].reg = p->from.offset&0xf;
	case D_REG:
		a[n].type = D_REG;
		a[n++].reg = p->from.reg;
	}
	if(n == 0)
		return 1;
	for(; r!=R && r!=r2; r=uniqs(r)) {
		p = r->prog;
		for(i=0; i<n; i++)
			if(copyu(p, &a[i], A) > 1)
				return 0;
	}
	return 1;
}

int
findu1(Reg *r, Adr *v)
{
	for(; r != R; r = r->s1) {
		if(r->active)
			return 0;
		r->active = 1;
		switch(copyu(r->prog, v, A)) {
		case 1: /* used */
		case 2: /* read-alter-rewrite */
		case 4: /* set and used */
			return 1;
		case 3: /* set */
			return 0;
		}
		if(r->s2)
			if (findu1(r->s2, v))
				return 1;
	}
	return 0;
}

int
finduse(Reg *r, Adr *v)
{
	Reg *r1;

	for(r1=firstr; r1!=R; r1=r1->link)
		r1->active = 0;
	return findu1(r, v);
}

#ifdef NOTYET
int
xtramodes(Reg *r, Adr *a)
{
	Reg *r1, *r2, *r3;
	Prog *p, *p1;
	Adr v;

	p = r->prog;
	if(debug['h'] && p->as == AMOVB && p->from.type == D_OREG)	/* byte load */
		return 0;
	v = *a;
	v.type = D_REG;
	r1 = findpre(r, &v);
	if(r1 != R) {
		p1 = r1->prog;
		if(p1->to.type == D_REG && p1->to.reg == v.reg)
		switch(p1->as) {
		case AADD:
			if(p1->from.type == D_REG ||
			   (p1->from.type == D_SHIFT && (p1->from.offset&(1<<4)) == 0 &&
			    (p->as != AMOVB || (a == &p->from && (p1->from.offset&~0xf) == 0))) ||
			   (p1->from.type == D_CONST && 
			    p1->from.offset > -4096 && p1->from.offset < 4096))
			if(nochange(uniqs(r1), r, p1)) {
				if(a != &p->from || v.reg != p->to.reg)
				if (finduse(r->s1, &v)) {
					if(p1->reg == NREG || p1->reg == v.reg)
						/* pre-indexing */
						p->scond |= C_WBIT;
					else return 0;	
				}
				switch (p1->from.type) {
				case D_REG:
					/* register offset */
					a->type = D_SHIFT;
					a->offset = p1->from.reg;
					break;
				case D_SHIFT:
					/* scaled register offset */
					a->type = D_SHIFT;
				case D_CONST:
					/* immediate offset */
					a->offset = p1->from.offset;
					break;
				}
				if(p1->reg != NREG)
					a->reg = p1->reg;
				excise(r1);
				return 1;
			}
			break;
		case AMOVW:
			if(p1->from.type == D_REG)
			if((r2 = findinc(r1, r, &p1->from)) != R) {
			for(r3=uniqs(r2); r3->prog->as==ANOP; r3=uniqs(r3))
				;
			if(r3 == r) {
				/* post-indexing */
				p1 = r2->prog;
				a->reg = p1->to.reg;
				a->offset = p1->from.offset;
				p->scond |= C_PBIT;
				if(!finduse(r, &r1->prog->to))
					excise(r1);
				excise(r2);
				return 1;
			}
			}
			break;
		}
	}
	if(a != &p->from || a->reg != p->to.reg)
	if((r1 = findinc(r, R, &v)) != R) {
		/* post-indexing */
		p1 = r1->prog;
		a->offset = p1->from.offset;
		p->scond |= C_PBIT;
		excise(r1);
		return 1;
	}
	return 0;
}
#endif

/*
 * return
 * 1 if v only used (and substitute),
 * 2 if read-alter-rewrite
 * 3 if set
 * 4 if set and used
 * 0 otherwise (not touched)
 */
int
copyu(Prog *p, Adr *v, Adr *s)
{

	switch(p->as) {

	default:
		if(debug['P'])
			print(" (unk)");
		return 2;

	case ANOP:	/* read, write */
	case AFMOVS:
	case AFMOVD:
	case AMOVH:
	case AMOVHU:
	case AMOVB:
	case AMOVBU:
	case AMOVW:
	case AMOVWU:
	case ASXTW:
	case AMOV:
	case AMVN:
	case AMVNW:
	case ANEG:
	case ANEGS:
	case ANEGW:
	case ANEGSW:
	case ANGC:
	case ANGCS:
	case ANGCW:
	case ANGCSW:
	case AFCVTSD:
	case AFCVTDS:
	case AFCVTZSD:
	case AFCVTZSDW:
	case AFCVTZSS:
	case AFCVTZSSW:
	case AFCVTZUD:
	case AFCVTZUDW:
	case AFCVTZUS:
	case AFCVTZUSW:
	case ASCVTFD:
	case ASCVTFS:
	case ASCVTFWD:
	case ASCVTFWS:
	case AUCVTFD:
	case AUCVTFS:
	case AUCVTFWD:
	case AUCVTFWS:
	case AFNEGD:
	case AFNEGS:
	case AFABSD:
	case AFABSS:
	case AFSQRTD:
	case AFSQRTS:
	case ACASE:
#ifdef YYY
		if(p->scond&(C_WBIT|C_PBIT))
		if(v->type == D_REG) {
			if(p->from.type == D_OREG || p->from.type == D_SHIFT) {
				if(p->from.reg == v->reg)
					return 2;
			} else {
		  		if(p->to.reg == v->reg)
					return 2;
			}
		}
#endif
		if(s != A) {
			if(copysub(&p->from, v, s, 1))
				return 1;
			if(!copyas(&p->to, v))
				if(copysub(&p->to, v, s, 1))
					return 1;
			return 0;
		}
		if(copyas(&p->to, v)) {
			if(copyau(&p->from, v))
				return 4;
			return 3;
		}
		if(copyau(&p->from, v))
			return 1;
		if(copyau(&p->to, v))
			return 1;
		return 0;


	case AADD:	/* read, read, write */
	case AADDW:
	case AADDS:
	case AADDSW:
	case ASUB:
	case ASUBW:
	case ASUBS:
	case ASUBSW:
		if(0 && p->from.type == D_CONST){
			if(s != A && regzer(s))
				return 4;	/* add/sub $c,r,r -> r31 is sp not zr, don't touch */
		}

	case ALSL:
	case ALSLW:
	case ALSR:
	case ALSRW:
	case AASR:
	case AASRW:
	case AROR:
	case ARORW:
	case AORR:
	case AORRW:
	case AAND:
	case AANDW:
	case AEOR:
	case AEORW:
	case AMUL:
	case AMULW:
	case AUMULL:
	case AREM:
	case AREMW:
	case ASDIV:
	case ASDIVW:
	case AUDIV:
	case AUDIVW:
	case AUREM:
	case AUREMW:
	case AFADDS:
	case AFADDD:
	case AFSUBS:
	case AFSUBD:
	case AFMULS:
	case AFMULD:
	case AFDIVS:
	case AFDIVD:
		if(s != A) {
			if(copysub(&p->from, v, s, 1))
				return 1;
			if(copysub1(p, v, s, 1))
				return 1;
			if(!copyas(&p->to, v))
				if(copysub(&p->to, v, s, 1))
					return 1;
			return 0;
		}
		if(copyas(&p->to, v)) {
			if(p->reg == NREG)
				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 ABEQ:	/* read, read */
	case ABNE:
	case ABCS:
	case ABHS:
	case ABCC:
	case ABLO:
	case ABMI:
	case ABPL:
	case ABVS:
	case ABVC:
	case ABHI:
	case ABLS:
	case ABGE:
	case ABLT:
	case ABGT:
	case ABLE:

	case AFCMPS:
	case AFCMPD:
	case ACMP:
	case ACMPW:
	case ACMN:
	case ACMNW:
	case ACBZ:
	case ACBZW:
	case ACBNZ:
	case ACBNZW:
	case ATBZ:
	case ATBNZ:
		if(s != A) {
			if(copysub(&p->from, v, s, 1))
				return 1;
			return copysub1(p, v, s, 1);
		}
		if(copyau(&p->from, v))
			return 1;
		if(copyau1(p, v))
			return 1;
		return 0;

	case AB:	/* funny */
		if(s != A) {
			if(copysub(&p->to, v, s, 1))
				return 1;
			return 0;
		}
		if(copyau(&p->to, v))
			return 1;
		return 0;

	case ARET:
	case ARETURN:	/* funny */
		if(v->type == D_REG)
		if(v->reg == REGRET)
			return 2;
		if(v->type == D_FREG)
		if(v->reg == FREGRET)
			return 2;

	case ABL:	/* funny */
		if(v->type == D_REG) {
			if(v->reg <= REGEXT && v->reg > exregoffset)
				return 2;
			if(v->reg == REGARG)
				return 2;
		}
		if(v->type == D_FREG)
			if(v->reg <= FREGEXT && v->reg > exfregoffset)
				return 2;

		if(s != A) {
			if(copysub(&p->to, v, s, 1))
				return 1;
			return 0;
		}
		if(copyau(&p->to, v))
			return 4;
		return 3;

	case ATEXT:	/* funny */
		if(v->type == D_REG)
			if(v->reg == REGARG)
				return 3;
		return 0;
	}
}

int
a2type(Prog *p)
{

	switch(p->as) {

	case ACMP:
	case ACMPW:
	case ACMN:
	case ACMNW:
	case ACBZ:
	case ACBZW:
	case ACBNZ:
	case ACBNZW:
	case ATBZ:
	case ATBNZ:

	case AADD:
	case AADDW:
	case AADDS:
	case AADDSW:
	case ASUB:
	case ASUBS:
	case ASUBSW:
	case ASUBW:
	case ALSL:
	case ALSLW:
	case ALSR:
	case ALSRW:
	case AASR:
	case AASRW:
	case AROR:
	case ARORW:
	case AORR:
	case AORRW:
	case AAND:
	case AANDW:
	case AANDS:
	case AANDSW:
	case AEOR:
	case AEORW:
	case AMUL:
	case AMULW:
	case AUMULL:
	case AREM:
	case AREMW:
	case ASDIV:
	case ASDIVW:
	case AUDIV:
	case AUDIVW:
	case AUREM:
	case AUREMW:
		return D_REG;

	case AFCMPS:
	case AFCMPD:

	case AFADDS:
	case AFADDD:
	case AFSUBS:
	case AFSUBD:
	case AFMULS:
	case AFMULD:
	case AFDIVS:
	case AFDIVD:
		return D_FREG;
	}
	return D_NONE;
}

/*
 * direct reference,
 * could be set/use depending on
 * semantics
 */
int
copyas(Adr *a, Adr *v)
{
	if(regtyp(v)) {
		if(a->type == v->type)
		if(a->reg == v->reg)
			return 1;
	} else {
		if(a->type == v->type)
		if(a->name == v->name)
		if(a->sym == v->sym)
		if(a->reg == v->reg){
			if(a->type == D_FCONST){
				if(a->dval == v->dval)
					return 1;
			} else if(a->offset == v->offset)
				return 1;
		}
	}
	return 0;
}

/*
 * either direct or indirect
 */
int
copyau(Adr *a, Adr *v)
{
	if(copyas(a, v))
		return 1;
	if(v->type == D_REG) {
		if(a->type == D_OREG) {
			if(v->reg == a->reg)
				return 1;
		} else if(a->type == D_SHIFT) {
			if(((a->offset>>16)&0x1F) == v->reg)
				return 1;
		} else if(a->type == D_EXTREG) {
			if(a->reg == v->reg || ((a->offset>>16)&0x1F) == v->reg)
				return 1;
		}
	}
	return 0;
}

int
copyau1(Prog *p, Adr *v)
{

	if(regtyp(v)) {
		if(a2type(p) == v->type)
		if(p->reg == v->reg) {
			if(a2type(p) != v->type)
				print("botch a2type %P\n", p);
			return 1;
		}
	}
	return 0;
}

/*
 * substitute s for v in a
 * return failure to substitute
 */
int
copysub(Adr *a, Adr *v, Adr *s, int f)
{

	if(f)
	if(copyau(a, v)) {
		if(a->type == D_SHIFT) {
			if(((a->offset>>16)&0x1F) == v->reg)
				a->offset = (a->offset&~(0x1F<<16))|(s->reg<<16);
		} else
			a->reg = s->reg;
	}
	return 0;
}

int
copysub1(Prog *p1, Adr *v, Adr *s, int f)
{

	if(f)
	if(copyau1(p1, v))
		p1->reg = s->reg;
	return 0;
}

struct {
	int opcode;
	int notopcode;
	int scond; 
	int notscond; 
} predinfo[]  = { 
	{ ABEQ,	ABNE,	0x0,	0x1, }, 
	{ ABNE,	ABEQ,	0x1,	0x0, }, 
	{ ABCS,	ABCC,	0x2,	0x3, }, 
	{ ABHS,	ABLO,	0x2,	0x3, }, 
	{ ABCC,	ABCS,	0x3,	0x2, }, 
	{ ABLO,	ABHS,	0x3,	0x2, }, 
	{ ABMI,	ABPL,	0x4,	0x5, }, 
	{ ABPL,	ABMI,	0x5,	0x4, }, 
	{ ABVS,	ABVC,	0x6,	0x7, }, 
	{ ABVC,	ABVS,	0x7,	0x6, }, 
	{ ABHI,	ABLS,	0x8,	0x9, }, 
	{ ABLS,	ABHI,	0x9,	0x8, }, 
	{ ABGE,	ABLT,	0xA,	0xB, }, 
	{ ABLT,	ABGE,	0xB,	0xA, }, 
	{ ABGT,	ABLE,	0xC,	0xD, }, 
	{ ABLE,	ABGT,	0xD,	0xC, }, 
}; 

typedef struct {
	Reg *start;
	Reg *last;
	Reg *end;
	int len;
} Joininfo;

enum {
	Join,
	Split,
	End,
	Branch,
	Setcond,
	Toolong
};
	
enum {
	Falsecond,
	Truecond,
	Delbranch,
	Keepbranch
};

int 
isbranch(Prog *p)
{
	return (ABEQ <= p->as) && (p->as <= ABLE); 
}

int
predicable(Prog *p)
{
	if (isbranch(p)
		|| p->as == ANOP
		|| p->as == AXXX
		|| p->as == ADATA
		|| p->as == AGLOBL
		|| p->as == AGOK
		|| p->as == AHISTORY
		|| p->as == ANAME
		|| p->as == ASIGNAME
		|| p->as == ATEXT
		|| p->as == AWORD
		|| p->as == ADYNT
		|| p->as == AINIT
		|| p->as == ABCASE
		|| p->as == ACASE)
		return 0; 
	return 1; 
}

/* 
 * Depends on an analysis of the encodings performed by 5l. 
 * These seem to be all of the opcodes that lead to the "S" bit
 * being set in the instruction encodings. 
 * 
 * C_SBIT may also have been set explicitly in p->scond.
 */ 
int
modifiescpsr(Prog *p)
{
//	return (p->scond&C_SBIT)
	return 1
		|| p->as == ATST 
		|| p->as == ACMN
		|| p->as == ACMP
		|| p->as == AUMULL
		|| p->as == AUDIV
		|| p->as == AMUL
		|| p->as == ASDIV
		|| p->as == AREM
		|| p->as == AUREM
		|| p->as == ABL;
} 

/*
 * Find the maximal chain of instructions starting with r which could
 * be executed conditionally
 */
int
joinsplit(Reg *r, Joininfo *j)
{
	j->start = r;
	j->last = r;
	j->len = 0;
	do {
		if (r->p2 && (r->p1 || r->p2->p2link)) {
			j->end = r;
			return Join;
		}
		if (r->s1 && r->s2) {
			j->end = r;
			return Split;
		}
		j->last = r;
		if (r->prog->as != ANOP)
			j->len++;
		if (!r->s1 && !r->s2) {
			j->end = r->link;
			return End;
		}
		if (r->s2) {
			j->end = r->s2;
			return Branch;
		}
		if (modifiescpsr(r->prog)) {
			j->end = r->s1;
			return Setcond;
		}
		r = r->s1;
	} while (j->len < 4);
	j->end = r;
	return Toolong;
}

Reg *
successor(Reg *r)
{
	if (r->s1)
		return r->s1; 
	else
		return r->s2; 
}

#ifdef XXX
void
applypred(Reg *rstart, Joininfo *j, int cond, int branch)
{
	int pred; 
	Reg *r; 

	if(j->len == 0)
		return;
	if (cond == Truecond)
		pred = predinfo[rstart->prog->as - ABEQ].scond;
	else
		pred = predinfo[rstart->prog->as - ABEQ].notscond; 
	
	for (r = j->start; ; r = successor(r)) {
		if (r->prog->as == AB) {
			if (r != j->last || branch == Delbranch)
				excise(r);
			else {
			  if (cond == Truecond)
				r->prog->as = predinfo[rstart->prog->as - ABEQ].opcode;
			  else
				r->prog->as = predinfo[rstart->prog->as - ABEQ].notopcode;
			}
		}
		else if (predicable(r->prog)) 
			r->prog->scond = (r->prog->scond&~C_SCOND)|pred;
		if (r->s1 != r->link) {
			r->s1 = r->link;
			r->link->p1 = r;
		}
		if (r == j->last)
			break;
	}
}


void
predicate(void)
{	
	Reg *r;
	int t1, t2;
	Joininfo j1, j2;

	for(r=firstr; r!=R; r=r->link) {
		if (isbranch(r->prog)) {
			t1 = joinsplit(r->s1, &j1);
			t2 = joinsplit(r->s2, &j2);
			if(j1.last->link != j2.start)
				continue;
			if(j1.end == j2.end)
			if((t1 == Branch && (t2 == Join || t2 == Setcond)) ||
			   (t2 == Join && (t1 == Join || t1 == Setcond))) {
				applypred(r, &j1, Falsecond, Delbranch);
				applypred(r, &j2, Truecond, Delbranch);
				excise(r);
				continue;
			}
			if(t1 == End || t1 == Branch) {
				applypred(r, &j1, Falsecond, Keepbranch);
				excise(r);
				continue;
			}
		} 
	} 
}
#endif