span.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

#include	"l.h"

static struct {
	ulong	start;
	ulong	size;
} pool;

void	checkpool(Prog*);
void 	flushpool(Prog*, int);

void
span(void)
{
	Prog *p;
	Sym *setext, *s;
	Optab *o;
	int m, bflag, i;
	long c, otxt, v;

	if(debug['v'])
		Bprint(&bso, "%5.2f span\n", cputime());
	Bflush(&bso);

	bflag = 0;
	c = INITTEXT;
	otxt = c;
	for(p = firstp; p != P; p = p->link) {
		p->pc = c;
		o = oplook(p);
		m = o->size;
		if(m == 0) {
			if(p->as == ATEXT) {
				curtext = p;
				autosize = p->to.offset + 4;
				if(p->from.sym != S)
					p->from.sym->value = c;
				/* need passes to resolve branches */
				if(c-otxt >= 1L<<17)
					bflag = 1;
				otxt = c;
				continue;
			}
			diag("zero-width instruction\n%P", p);
			continue;
		}
		switch(o->flag & (LFROM|LTO|LPOOL)) {
		case LFROM:
			addpool(p, &p->from);
			break;
		case LTO:
			addpool(p, &p->to);
			break;
		case LPOOL:
			if ((p->scond&C_SCOND) == 14)
				flushpool(p, 0);
			break;
		}
		if(p->as==AMOVW && p->to.type==D_REG && p->to.reg==REGPC && (p->scond&C_SCOND) == 14)
			flushpool(p, 0);
		c += m;
		if(blitrl)
			checkpool(p);
	}

	/*
	 * 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.
	 */
	while(bflag) {
		if(debug['v'])
			Bprint(&bso, "%5.2f span1\n", cputime());
		bflag = 0;
		c = INITTEXT;
		for(p = firstp; p != P; p = p->link) {
			p->pc = c;
			o = oplook(p);
/* very larg branches
			if(o->type == 6 && p->cond) {
				otxt = p->cond->pc - c;
				if(otxt < 0)
					otxt = -otxt;
				if(otxt >= (1L<<17) - 10) {
					q = prg();
					q->link = p->link;
					p->link = q;
					q->as = AB;
					q->to.type = D_BRANCH;
					q->cond = p->cond;
					p->cond = q;
					q = prg();
					q->link = p->link;
					p->link = q;
					q->as = AB;
					q->to.type = D_BRANCH;
					q->cond = q->link->link;
					bflag = 1;
				}
			}
 */
			m = o->size;
			if(m == 0) {
				if(p->as == ATEXT) {
					curtext = p;
					autosize = p->to.offset + 4;
					if(p->from.sym != S)
						p->from.sym->value = c;
					continue;
				}
				diag("zero-width instruction\n%P", p);
				continue;
			}
			c += m;
		}
	}

	if(debug['t']) {
		/* 
		 * add strings to text segment
		 */
		c = rnd(c, 8);
		for(i=0; i<NHASH; i++)
		for(s = hash[i]; s != S; s = s->link) {
			if(s->type != SSTRING)
				continue;
			v = s->value;
			while(v & 3)
				v++;
			s->value = c;
			c += v;
		}
	}

	c = rnd(c, 8);

	setext = lookup("etext", 0);
	if(setext != S) {
		setext->value = c;
		textsize = c - INITTEXT;
	}
	if(INITRND)
		INITDAT = rnd(c, INITRND);
	if(debug['v'])
		Bprint(&bso, "tsize = %lux\n", textsize);
	Bflush(&bso);
}

/*
 * when the first reference to the literal pool threatens
 * to go out of range of a 12-bit PC-relative offset,
 * drop the pool now, and branch round it.
 * this happens only in extended basic blocks that exceed 4k.
 */
void
checkpool(Prog *p)
{
	if(pool.size >= 0xffc || immaddr((p->pc+4)+4+pool.size - pool.start+8) == 0)
		flushpool(p, 1);
	else if(p->link == P)
		flushpool(p, 2);
}

void
flushpool(Prog *p, int skip)
{
	Prog *q;

	if(blitrl) {
		if(skip){
			if(debug['v'] && skip == 1)
				print("note: flush literal pool at %lux: len=%lud ref=%lux\n", p->pc+4, pool.size, pool.start);
			q = prg();
			q->as = AB;
			q->to.type = D_BRANCH;
			q->cond = p->link;
			q->link = blitrl;
			blitrl = q;
		}
		else if(p->pc+pool.size-pool.start < 2048)
			return;
		elitrl->link = p->link;
		p->link = blitrl;
		blitrl = 0;	/* BUG: should refer back to values until out-of-range */
		elitrl = 0;
		pool.size = 0;
		pool.start = 0;
	}
}

void
addpool(Prog *p, Adr *a)
{
	Prog *q, t;
	int c;

	c = aclass(a);

	t = zprg;
	t.as = AWORD;

	switch(c) {
	default:
		t.to = *a;
		break;

	case C_SROREG:
	case C_LOREG:
	case C_ROREG:
	case C_FOREG:
	case C_SOREG:
	case C_FAUTO:
	case C_SAUTO:
	case C_LAUTO:
	case C_LACON:
		t.to.type = D_CONST;
		t.to.offset = instoffset;
		break;
	}

	for(q = blitrl; q != P; q = q->link)	/* could hash on t.t0.offset */
		if(memcmp(&q->to, &t.to, sizeof(t.to)) == 0) {
			p->cond = q;
			return;
		}

	q = prg();
	*q = t;
	q->pc = pool.size;

	if(blitrl == P) {
		blitrl = q;
		pool.start = p->pc;
	} else
		elitrl->link = q;
	elitrl = q;
	pool.size += 4;

	p->cond = q;
}

void
xdefine(char *p, int t, long v)
{
	Sym *s;

	s = lookup(p, 0);
	if(s->type == 0 || s->type == SXREF) {
		s->type = t;
		s->value = v;
	}
}

long
regoff(Adr *a)
{

	instoffset = 0;
	aclass(a);
	return instoffset;
}

long
immrot(ulong v)
{
	int i;

	for(i=0; i<16; i++) {
		if((v & ~0xff) == 0)
			return (i<<8) | v | (1<<25);
		v = (v<<2) | (v>>30);
	}
	return 0;
}

long
immaddr(long v)
{
	if(v >= 0 && v <= 0xfff)
		return (v & 0xfff) |
			(1<<24) |	/* pre indexing */
			(1<<23);	/* pre indexing, up */
	if(v >= -0xfff && v < 0)
		return (-v & 0xfff) |
			(1<<24);	/* pre indexing */
	return 0;
}

int
immfloat(long v)
{
	return (v & 0xC03) == 0;	/* offset will fit in floating-point load/store */
}

int
immhalf(long v)
{
	if(v >= 0 && v <= 0xff)
		return v|
			(1<<24)|	/* pre indexing */
			(1<<23);	/* pre indexing, up */
	if(v >= -0xff && v < 0)
		return (-v & 0xff)|
			(1<<24);	/* pre indexing */
	return 0;
}

int
aclass(Adr *a)
{
	Sym *s;
	int t;

	switch(a->type) {
	case D_NONE:
		return C_NONE;

	case D_REG:
		return C_REG;

	case D_REGREG:
		return C_REGREG;

	case D_SHIFT:
		return C_SHIFT;

	case D_FREG:
		return C_FREG;

	case D_FPCR:
		return C_FCR;

	case D_OREG:
		switch(a->name) {
		case D_EXTERN:
		case D_STATIC:
			if(a->sym == 0 || a->sym->name == 0) {
				print("null sym external\n");
				print("%D\n", a);
				return C_GOK;
			}
			s = a->sym;
			t = s->type;
			if(t == 0 || t == SXREF) {
				diag("undefined external: %s in %s",
					s->name, TNAME);
				s->type = SDATA;
			}
			if(dlm) {
				switch(t) {
				default:
					instoffset = s->value + a->offset + INITDAT;
					break;
				case SUNDEF:
				case STEXT:
				case SCONST:
				case SLEAF:
				case SSTRING:
					instoffset = s->value + a->offset;
					break;
				}
				return C_ADDR;
			}
			instoffset = s->value + a->offset - BIG;
			t = immaddr(instoffset);
			if(t) {
				if(immhalf(instoffset))
					return immfloat(t) ? C_HFEXT : C_HEXT;
				if(immfloat(t))
					return C_FEXT;
				return C_SEXT;
			}
			return C_LEXT;
		case D_AUTO:
			instoffset = autosize + a->offset;
			t = immaddr(instoffset);
			if(t){
				if(immhalf(instoffset))
					return immfloat(t) ? C_HFAUTO : C_HAUTO;
				if(immfloat(t))
					return C_FAUTO;
				return C_SAUTO;
			}
			return C_LAUTO;

		case D_PARAM:
			instoffset = autosize + a->offset + 4L;
			t = immaddr(instoffset);
			if(t){
				if(immhalf(instoffset))
					return immfloat(t) ? C_HFAUTO : C_HAUTO;
				if(immfloat(t))
					return C_FAUTO;
				return C_SAUTO;
			}
			return C_LAUTO;
		case D_NONE:
			instoffset = a->offset;
			t = immaddr(instoffset);
			if(t) {
				if(immhalf(instoffset))		 /* n.b. that it will also satisfy immrot */
					return immfloat(t) ? C_HFOREG : C_HOREG;
				if(immfloat(t))
					return C_FOREG; /* n.b. that it will also satisfy immrot */
				t = immrot(instoffset);
				if(t)
					return C_SROREG;
				if(immhalf(instoffset))
					return C_HOREG;
				return C_SOREG;
			}
			t = immrot(instoffset);
			if(t)
				return C_ROREG;
			return C_LOREG;
		}
		return C_GOK;

	case D_PSR:
		return C_PSR;

	case D_OCONST:
		switch(a->name) {
		case D_EXTERN:
		case D_STATIC:
			s = a->sym;
			t = s->type;
			if(t == 0 || t == SXREF) {
				diag("undefined external: %s in %s",
					s->name, TNAME);
				s->type = SDATA;
			}
			instoffset = s->value + a->offset + INITDAT;
			if(s->type == STEXT || s->type == SLEAF || s->type == SUNDEF)
				instoffset = s->value + a->offset;
			return C_LCON;
		}
		return C_GOK;

	case D_FCONST:
		return C_FCON;

	case D_CONST:
		switch(a->name) {

		case D_NONE:
			instoffset = a->offset;
			if(a->reg != NREG)
				goto aconsize;

			t = immrot(instoffset);
			if(t)
				return C_RCON;
			t = immrot(~instoffset);
			if(t)
				return C_NCON;
			return C_LCON;

		case D_EXTERN:
		case D_STATIC:
			s = a->sym;
			if(s == S)
				break;
			t = s->type;
			switch(t) {
			case 0:
			case SXREF:
				diag("undefined external: %s in %s",
					s->name, TNAME);
				s->type = SDATA;
				break;
			case SUNDEF:
			case STEXT:
			case SSTRING:
			case SCONST:
			case SLEAF:
				instoffset = s->value + a->offset;
				return C_LCON;
			}
			if(!dlm) {
				instoffset = s->value + a->offset - BIG;
				t = immrot(instoffset);
				if(t && instoffset != 0)
					return C_RECON;
			}
			instoffset = s->value + a->offset + INITDAT;
			return C_LCON;

		case D_AUTO:
			instoffset = autosize + a->offset;