noop.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

				p = q;
				break;
			}
			if(p->from.type != D_REG){
				diag("bad instruction %P", p);
				break;
			}
			o = p->as;
			q = genIRR(p, ASUBQ, 16LL, NREG, REGSP);
			q = genstore(q, AMOVQ, p->from.reg, 8LL, REGSP);
			if (o == ADIVL || o == ADIVL || o == AMODL || o == AMODLU)
				q->as = AMOVL;

			q = genRRR(q, AMOVQ, p->reg, NREG, REGTMP);
			if (p->reg == NREG)
				q->from.reg = p->to.reg;

			/* CALL appropriate */
			q1 = prg();
			q1->link = q->link;
			q->link = q1;

			q1->as = AJSR;
			q1->line = p->line;
			q1->to.type = D_BRANCH;
			q1->cond = divsubr(o);
			q1->mark |= BRANCH;
			q = q1;

			q = genRRR(q, AMOVQ, REGTMP, NREG, p->to.reg);
			q = genIRR(q, AADDQ, 16LL, NREG, REGSP);
			excise(p);
			p = q;
			break;

		/* Attempt to replace {cond. branch, mov} with a cmov */
		/* XXX warning: this is all a bit experimental */
		case ABEQ:
		case ABNE:
		case ABGE:
		case ABGT:
		case ABLE:
		case ABLT:
		case ABLBC:
		case ABLBS:
			q = p->link;
			if (q == P)
				break;
			q1 = q->link;
			if (q1 != p->cond || q1 == P)
				break;
/*print("%P\n", q); /* */
			if (q->to.type != D_REG)
				break;
			if (q->from.type != D_REG && (q->from.type != D_CONST || q->from.name != D_NONE))
				break;
			if (q->mark&LABEL2)
				break;
/* print("%P\n", q); /* */
			if (q->as != AMOVQ)		/* XXX can handle more than this! */
				break;
			q->as = (p->as^1) + ACMOVEQ-ABEQ;	/* sleazy hack */
			q->reg = p->from.reg;		/* XXX check CMOVx operand order! */
			excise(p);		/* XXX p's LABEL? */
			if (!(q1->mark&LABEL2))
				q1->mark &= ~LABEL;
			break;
		case AFBEQ:
		case AFBNE:
		case AFBGE:
		case AFBGT:
		case AFBLE:
		case AFBLT:
			q = p->link;
			if (q == P)
				break;
			q1 = q->link;
			if (q1 != p->cond || q1 == P)
				break;
			if (q->from.type != D_FREG || q->to.type != D_FREG)
				break;
/* print("%P\n", q); /* */
			if (q->mark&LABEL2)
				break;
			if (q->as != AMOVT)		/* XXX can handle more than this! */
				break;
			q->as = (p->as^1) + AFCMOVEQ-AFBEQ;	/* sleazy hack */
			q->reg = p->from.reg;		/* XXX check CMOVx operand order! */
			excise(p);		/* XXX p's LABEL? */
			if (!(q1->mark&LABEL2))
				q1->mark &= ~LABEL;
			break;
		}
	}

	curtext = P;
	q = P;		/* p - 1 */
	q1 = firstp;	/* top of block */
	o = 0;		/* count of instructions */
	for(p = firstp; p != P; p = p1) {
		p1 = p->link;
		o++;
		if(p->mark & NOSCHED){
			if(q1 != p){
				sched(q1, q);
			}
			for(; p != P; p = p->link){
				if(!(p->mark & NOSCHED))
					break;
				q = p;
			}
			p1 = p;
			q1 = p;
			o = 0;
			continue;
		}
		if(p->mark & (LABEL|SYNC)) {
			if(q1 != p)
				sched(q1, q);
			q1 = p;
			o = 1;
		}
		if(p->mark & (BRANCH|SYNC)) {
			sched(q1, p);
			q1 = p1;
			o = 0;
		}
		if(o >= NSCHED) {
			sched(q1, p);
			q1 = p1;
			o = 0;
		}
		q = p;
	}
}

void
nocache(Prog *p)
{
	p->optab = 0;
	p->from.class = 0;
	p->to.class = 0;
}

/* XXX use of this may lose important LABEL flags, check that this isn't happening (or fix) */
void
excise(Prog *p)
{
	Prog *q;

	q = p->link;
	*p = *q;
}

void
initdiv(void)
{
	Sym *s1, *s2, *s3, *s4, *s5, *s6, *s7, *s8;
	Prog *p;

	s1 = lookup("_divq", 0);
	s2 = lookup("_divqu", 0);
	s3 = lookup("_modq", 0);
	s4 = lookup("_modqu", 0);
	s5 = lookup("_divl", 0);
	s6 = lookup("_divlu", 0);
	s7 = lookup("_modl", 0);
	s8 = lookup("_modlu", 0);
	for(p = firstp; p != P; p = p->link)
		if(p->as == ATEXT) {
			if(p->from.sym == s1)
				prog_divq = p;
			if(p->from.sym == s2)
				prog_divqu = p;
			if(p->from.sym == s3)
				prog_modq = p;
			if(p->from.sym == s4)
				prog_modqu = p;
			if(p->from.sym == s5)
				prog_divl = p;
			if(p->from.sym == s6)
				prog_divlu = p;
			if(p->from.sym == s7)
				prog_modl = p;
			if(p->from.sym == s8)
				prog_modlu = p;
		}
	if(prog_divq == P) {
		diag("undefined: %s", s1->name);
		prog_divq = curtext;
	}
	if(prog_divqu == P) {
		diag("undefined: %s", s2->name);
		prog_divqu = curtext;
	}
	if(prog_modq == P) {
		diag("undefined: %s", s3->name);
		prog_modq = curtext;
	}
	if(prog_modqu == P) {
		diag("undefined: %s", s4->name);
		prog_modqu = curtext;
	}
	if(prog_divl == P) {
		diag("undefined: %s", s5->name);
		prog_divl = curtext;
	}
	if(prog_divlu == P) {
		diag("undefined: %s", s6->name);
		prog_divlu = curtext;
	}
	if(prog_modl == P) {
		diag("undefined: %s", s7->name);
		prog_modl = curtext;
	}
	if(prog_modlu == P) {
		diag("undefined: %s", s8->name);
		prog_modlu = curtext;
	}
}

Prog *
divsubr(int o)
{
	switch(o) {
	case ADIVQ:
		return prog_divq;
	case ADIVQU:
		return prog_divqu;
	case AMODQ:
		return prog_modq;
	case AMODQU:
		return prog_modqu;
	case ADIVL:
		return prog_divl;
	case ADIVLU:
		return prog_divlu;
	case AMODL:
		return prog_modl;
	case AMODLU:
		return prog_modlu;
	default:
		diag("bad op %O in divsubr", o);
		return prog_modlu;
	}
}

Prog*
divuconst(Prog *p, uvlong y, int num, int quot, int bits)
{
	int logy, i, shift;
	uvlong k, m, n, mult, tmp, msb;

	if(num == NREG)
		num = quot;
	if(y == 0) {
		diag("division by zero");
		return p;
	}
	if(y == 1)
		return genRRR(p, AMOVQ, num, NREG, quot);

	if(num == REGTMP || quot == REGTMP)
		diag("bad register in divuconst");

	tmp = y;
	for(logy = -1; tmp != 0; logy++)
		tmp >>= 1;

	msb = (1LL << (bits-1));
	if((y & (y-1)) == 0)		/* power of 2 */
		return genIRR(p, ASRLQ, logy, num, quot);
	if(y > msb)
		return genIRR(p, ACMPUGE, y, num, quot);

	/* k = (-2^(bits+logy)) % y */
	m = msb/y;
	n = msb%y;
	if(debug['d'])
		Bprint(&bso, "divuconst: y=%lld msb=%lld m=%lld n=%lld\n",
			y, msb, m, n);
	for(i = 0; i <= logy; i++) {
		m *= 2LL;
		n *= 2LL;
		if(n > y) {
			m += 1LL;
			n -= y;
		}
	}
	if(debug['d'])
		Bprint(&bso, "divuconst: y=%lld msb=%lld m=%lld n=%lld\n",
			y, msb, m, n);
	k = y - n;
	if(k > (1LL << logy)) {
		mult = 2LL*m + 1LL;
		bits++;
	} else
		mult = m + 1LL;

	shift = bits + logy;
	if(debug['d'])
		Bprint(&bso, "divuconst: y=%lld mult=%lld shift=%d bits=%d k=%lld\n",
			y, mult, shift, bits, k);
	if(bits <= 32) {
		p = genIRR(p, AMOVQ, mult, NREG, REGTMP);
		p = genRRR(p, AEXTLL, REGZERO, num, quot);
		p = genRRR(p, AMULQ, REGTMP, quot, quot);
		p = genIRR(p, ASRLQ, shift, quot, quot);
		p = genRRR(p, AADDL, quot, REGZERO, quot);
		return p;
	}
	if(bits == 33) {
		if(shift < 64) {
			mult <<= (64-shift);
			shift = 64;
		}
		p = genIRR(p, AMOVQ, mult, NREG, REGTMP);
		p = genRRR(p, AEXTLL, REGZERO, num, quot);
		p = genRRR(p, AUMULH, REGTMP, quot, quot);
		if(shift != 64)
			p = genIRR(p, ASRLQ, shift-64, quot, quot);
		p = genRRR(p, AADDL, quot, REGZERO, quot);
		return p;
	}
	if(bits <= 64) {
		if(shift < 64) {
			mult <<= (64-shift);
			shift = 64;
		}
		p = genIRR(p, AMOVQ, mult, NREG, REGTMP);
		p = genRRR(p, AUMULH, REGTMP, num, quot);
		if(shift != 64)
			p = genIRR(p, ASRLQ, shift-64, quot, quot);
		return p;
	}

	p = genIRR(p, AMOVQ, mult, NREG, REGTMP);
	p = genRRR(p, AUMULH, REGTMP, num, REGTMP);
	p = genRRR(p, AADDQ, num, REGTMP, quot);
	p = genRRR(p, ACMPUGT, REGTMP, quot, REGTMP);
	p = genIRR(p, ASLLQ, 128-shift, REGTMP, REGTMP);
	p = genIRR(p, ASRLQ, shift-64, quot, quot);
	p = genRRR(p, AADDQ, REGTMP, quot, quot);
	return p;
}

Prog *
divconst(Prog *p, vlong y, int num, int quot, int bits)
{
	vlong yabs;
	Prog *q;

	yabs = y;
	if (y < 0)
		yabs = -y;
	q = genRRR(p, ASUBQ, num, REGZERO, REGTMP2);
	if (num != quot)
		q = genRRR(q, AMOVQ, num, NREG, quot);
	q = genRRR(q, ACMOVGT, REGTMP2, REGTMP2, quot);
	q = divuconst(q, yabs, quot, quot, bits-1);
	q = genRRR(q, ASUBQ, quot, REGZERO, REGTMP);
	q = genRRR(q, (y < 0)? ACMOVLT: ACMOVGT, REGTMP, REGTMP2, quot);
	return q;
}

Prog *
modconst(Prog *p, vlong y, int num, int quot, int bits)
{
	vlong yabs;
	Prog *q;

	yabs = y;
	if (y < 0)
		yabs = -y;
	q = genRRR(p, ASUBQ, num, REGZERO, REGTMP2);
	q = genRRR(q, ACMOVLT, num, REGTMP2, REGTMP2);
	q = divuconst(q, yabs, REGTMP2, REGTMP2, bits-1);
	q = genRRR(q, ASUBQ, REGTMP2, REGZERO, REGTMP);
	q = genRRR(q, ACMOVLT, REGTMP, num, REGTMP2);
	q = genIRR(q, AMULQ, yabs, REGTMP2, REGTMP2);
	q = genRRR(q, ASUBQ, REGTMP2, num, quot);
	return q;
}

Prog *
genXXX(Prog *q, int op, Adr *from, int reg, Adr *to)
{
	Prog *p;

	p = prg();
	p->as = op;
	p->line = q->line;
	p->from = *from;
	p->to = *to;
	p->reg = reg;
	p->link = q->link;
	q->link = p;
	return p;
}

Prog *
genRRR(Prog *q, int op, int from, int reg, int to)
{
	Prog *p;

	p = prg();
	p->as = op;
	p->line = q->line;
	p->from.type = D_REG;
	p->from.reg = from;
	p->to.type = D_REG;
	p->to.reg = to;
	p->reg = reg;
	p->link = q->link;
	q->link = p;
	return p;
}

Prog *
genIRR(Prog *q, int op, vlong v, int reg, int to)
{
	Prog *p;

	p = prg();
	p->as = op;
	p->line = q->line;
	p->from.type = D_CONST;
	p->from.offset = v;
	p->to.type = D_REG;
	p->to.reg = to;
	p->reg = reg;
	p->link = q->link;
	q->link = p;
	return p;
}

Prog *
genstore(Prog *q, int op, int from, vlong offset, int to)
{
	Prog *p;

	p = prg();
	p->as = op;
	p->line = q->line;
	p->from.type = D_REG;
	p->from.reg = from;
	p->to.type = D_OREG;
	p->to.reg = to;
	p->to.offset = offset;
	p->reg = NREG;
	p->link = q->link;
	q->link = p;
	return p;
}

Prog *
genload(Prog *q, int op, vlong offset, int from, int to)
{
	Prog *p;

	p = prg();
	p->as = op;
	p->line = q->line;
	p->from.type = D_OREG;
	p->from.offset = offset;
	p->from.reg = from;
	p->to.type = D_REG;
	p->to.reg = to;
	p->reg = NREG;
	p->link = q->link;
	q->link = p;
	return p;
}