txt.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

	if(g >= D_A0 && g < D_A0+NREG) {
		aregused[g-D_A0]++;
		return g;
	}
	for(g=0; g<NREG; g++)
		if(aregused[g] == 0) {
			aregused[g]++;
			return g + D_A0;
		}
	diag(Z, "out of addr registers");
	return D_TOS;
}

int
regpair(int g)
{

	if(g >= D_R0+1 && g < D_R0+NREG)
		if(!regused[g-D_R0-1]) {
			regused[g-D_R0-1]++;
			regused[g-D_R0]++;
			return g-1;
		}
	if(g >= D_R0 && g < D_R0+NREG-1)
		if(!regused[g-D_R0+1]) {
			regused[g-D_R0+1]++;
			regused[g-D_R0]++;
			return g;
		}
	for(g = 0; g < NREG-1; g++)
		if(!regused[g])
		if(!regused[g+1]) {
			regused[g]++;
			regused[g+1]++;
			return g + D_R0;
		}
	diag(Z, "out of register pairs");
	return D_TOS;
}

int
regret(Type *t)
{

	if(t == T)
		return D_NONE;
	if(typefd[t->etype])
		return D_F0;
	return D_R0;
}

void
regfree(int g)
{

	g &= D_MASK;
	if(g == D_TOS || g == D_TREE || g == D_NONE)
		return;
	if(g >= D_R0 && g < D_R0+NREG) {
		regused[g-D_R0]--;
		return;
	}
	if(g >= D_A0 && g < D_A0+NREG) {
		aregused[g-D_A0]--;
		return;
	}
	if(g >= D_F0 && g < D_F0+NREG) {
		fregused[g-D_F0]--;
		return;
	}
	diag(Z, "bad in regfree: %d", g);
}

void
gmove(Type *tf, Type *tt, int gf, Node *f, int gt, Node *t)
{
	int g, a, b;
	Prog *p1;

	tindex(tf, tt);
	if(txtp->preclr) {
		if(gf >= D_R0 && gf < D_R0+NREG)
		if(txtp->preclr < 0) {
			gmove(tt, tt, gf, f, gt, t);
			return;
		}
		g = regalloc(types[TLONG], gt);
		if(g == gf) {
			g = regalloc(types[TLONG], D_NONE);
			regfree(gf);
		}
		if(txtp->preclr > 0)
			gopcode(OAS, types[TLONG], D_CONST, nodconst(0), g, Z);
		gopcode(OAS, tf, gf, f, g, Z);
		if(g != gt)
			gopcode(OAS, tt, g, Z, gt, t);
		regfree(g);
		return;
	}
	a = txtp->postext;
	if(a != AGOK) {
		if(gf >= D_R0 && gf < D_R0+NREG)
			g = regalloc(types[TLONG], gf);
		else
			g = regalloc(types[TLONG], gt);
		if(g != gf)
			gopcode(OAS, tf, gf, f, g, Z);
		nextpc();
		p->as = a;
		p->to.type = g;
		if(debug['g'])
			print("%P\n", p);
		if(g != gt)
			gopcode(OAS, tt, g, Z, gt, t);
		regfree(g);
		return;
	}
	if((regbase[gf] != D_NONE && regbase[gf] == regbase[gt]) ||
	   (gf == D_TREE && gt == D_TREE && f == t))
		return;
	if(typefd[tf->etype] || typefd[tt->etype]) {
		if(typeu[tf->etype] && typefd[tt->etype]) {	/* unsign->float */
			a = regalloc(types[TLONG], D_NONE);
			gmove(tf, types[TLONG], gf, f, a, t);
			if(tf->etype == TULONG) {
				b = regalloc(types[TDOUBLE], D_NONE);
				gmove(types[TLONG], tt, a, t, b, t);
				gopcode(OTST, types[TLONG], D_NONE, Z, a, t);
				gbranch(OGE);
				p1 = p;
				gopcode(OASADD, types[TDOUBLE],
					D_CONST, nodconst(100), b, t);
				p->from.dval = 4294967296.;
				patch(p1, pc);
				gmove(types[TDOUBLE], tt, b, t, gt, t);
				regfree(b);
			} else
				gmove(types[TLONG], tt, a, t, gt, t);
			regfree(a);
			return;
		}
		if(typefd[tf->etype] && !typefd[tt->etype]) {	/* float->fix */
			a = regalloc(types[TLONG], D_NONE);
			gopcode(OAS, types[TLONG], D_FPCR, t, a, t);
			gopcode(OAS, types[TLONG], D_CONST, nodconst(16), D_FPCR, t);
		}
		if(gf < D_F0 || gf >= D_F0+NREG) {
			g = regalloc(types[TDOUBLE], gt);
			gopcode(OFAS, tf, gf, f, g, t);
			if(g != gt)
				gopcode(OFAS, tt, g, t, gt, t);
			regfree(g);
		} else
			gopcode(OFAS, tt, gf, f, gt, t);
		if(typefd[tf->etype] && !typefd[tt->etype]) {	/* float->fix */
			gopcode(OAS, types[TLONG], a, t, D_FPCR, t);
			regfree(a);
		}
		return;
	}
	gopcode(OAS, tt, gf, f, gt, t);
}

void
gopcode(int o, Type *ty, int gf, Node *f, int gt, Node *t)
{
	int i, fidx, tidx;

	if(o == OAS)
		if(gf == gt)
			if(gf != D_TREE || f == t)
				return;

	fidx = D_NONE;
	tidx = D_NONE;
	i = 0;
	if(ty != T) {
		i = ty->etype;
		if(i >= NTYPE)
			i = 0;
	}
	nextpc();
	if(gf == D_TREE) {
		naddr(f, &p->from, fidx);
	} else {
		p->from.type = gf;
		if(gf == D_CONST) {
			p->from.offset = (long)(uintptr)f;
			if(typefd[i]) {
				p->from.type = D_FCONST;
				p->from.dval = (long)(uintptr)f;
			}
		}
	}
	p->as = opxt[o][i];
	if(gt == D_TREE) {
		naddr(t, &p->to, tidx);
	} else {
		p->to.type = gt;
		if(gt == D_CONST)
			p->to.offset = (long)(uintptr)t;
	}
	if(o == OBIT) {
		p->from.field = f->type->nbits;
		p->to.field = f->type->shift;
		if(p->from.field == 0)
			diag(Z, "BIT zero width bit field");
	}
	if(p->as == AMOVL || p->as == AMOVW || p->as == AMOVB)
		asopt();
	if(debug['g'])
		print("%P\n", p);
	if(p->as == AGOK)
		diag(Z, "GOK in gopcode: %s", onames[o]);
	if(fidx != D_NONE)
		regfree(fidx);
	if(tidx != D_NONE)
		regfree(tidx);
}

void
asopt(void)
{
	long v;
	int g;
	Prog *q;

	/*
	 * mov $0, ...
	 * ==>
	 * clr , ...
	 */
	v = 0;
	if(p->from.type == D_CONST) {
		v = p->from.offset;
		if(v == 0) {
			p->from.type = D_NONE;
			if(p->as == AMOVL)
				p->as = ACLRL;
			if(p->as == AMOVW)
				p->as = ACLRW;
			if(p->as == AMOVB)
				p->as = ACLRB;
			return;
		}
	}
	/*
	 * mov ..., TOS
	 * ==>
	 * pea (...)
	 */
	if(p->as == AMOVL && p->to.type == D_TOS)
	switch(p->from.type) {
	case D_CONST:
		p->from.type |= I_INDIR;
		p->to = p->from;
		p->from = zprog.from;
		p->as = APEA;
		return;

	case I_ADDR|D_EXTERN:
	case I_ADDR|D_STATIC:
		p->from.type &= ~I_ADDR;
		p->to = p->from;
		p->from = zprog.from;
		p->as = APEA;
		return;
	}
	/*
	 * movL $Qx, ...
	 * ==>
	 * movL $Qx,R
	 * movL R, ...
	 */
	if(p->as == AMOVL && p->from.type == D_CONST)
	if(v >= -128 && v < 128)
	if(p->to.type < D_R0 || p->to.type >= D_R0+NREG) {
		g = regalloc(types[TLONG], D_NONE);
		q = p;
		nextpc();
		p->as = AMOVL;
		p->from.type = g;
		p->to = q->to;
		q->to = p->from;
		regfree(g);
		if(debug['g'])
			print("%P\n", q);
		return;
	}
}

void
gbranch(int o)
{
	int a;

	a = ABNE;
	switch(o) {
	case ORETURN: a = ARTS; break;
	case OGOTO: a = ABRA; break;
	case OEQ: a = ABEQ; break;
	case ONE: a = ABNE; break;
	case OLE: a = ABLE; break;
	case OLS: a = ABLS; break;
	case OLT: a = ABLT; break;
	case OLO: a = ABCS; break;
	case OGE: a = ABGE; break;
	case OHS: a = ABCC; break;
	case OGT: a = ABGT; break;
	case OHI: a = ABHI; break;
	case OBIT: a = ABCS; break;
	case OCASE: a = ABCASE; break;
	}
	nextpc();
	p->from.type = D_NONE;
	p->to.type = D_NONE;
	p->as = a;
}

void
fpbranch(void)
{
	int a;

	a = p->as;
	switch(a) {
	case ABEQ: a = AFBEQ; break;
	case ABNE: a = AFBNE; break;
	case ABLE: a = AFBLE; break;
	case ABLT: a = AFBLT; break;
	case ABGE: a = AFBGE; break;
	case ABGT: a = AFBGT; break;
	}
	p->as = a;
}

void
patch(Prog *op, long pc)
{

	op->to.offset = pc;
	op->to.type = D_BRANCH;
}

void
gpseudo(int a, Sym *s, int g, long v)
{

	nextpc();
	if(a == ADATA)
		pc--;
	p->as = a;
	p->to.type = g;
	p->to.offset = v;
	p->from.sym = s;
	p->from.type = D_EXTERN;
	if(s->class == CSTATIC)
		p->from.type = D_STATIC;
}

void
gpseudotree(int a, Sym *s, Node *n)
{

	nextpc();
	if(a == ADATA)
		pc--;
	p->as = a;
	naddr(n, &p->to, D_NONE);
	p->from.sym = s;
	p->from.type = D_EXTERN;
	if(s->class == CSTATIC)
		p->from.type = D_STATIC;
}

long
exreg(Type *t)
{
	long o;

	if(typechl[t->etype]) {
		if(exregoffset <= 5)
			return 0;
		o = exregoffset + D_R0;
		exregoffset--;
		return o;
	}
	if(t->etype == TIND) {
		if(exaregoffset <= 3)
			return 0;
		o = exaregoffset + D_A0;
		exaregoffset--;
		return o;
	}
	if(typefd[t->etype]) {
		if(exfregoffset <= 5)
			return 0;
		o = exfregoffset + D_F0;
		exfregoffset--;
		return o;
	}
	return 0;
}

schar	ewidth[NTYPE] =
{
	-1,		/* [TXXX] */
	SZ_CHAR,	/* [TCHAR] */
	SZ_CHAR,	/* [TUCHAR] */
	SZ_SHORT,	/* [TSHORT] */
	SZ_SHORT,	/* [TUSHORT] */
	SZ_INT,		/* [TINT] */
	SZ_INT,		/* [TUINT] */
	SZ_LONG,	/* [TLONG] */
	SZ_LONG,	/* [TULONG] */
	SZ_VLONG,	/* [TVLONG] */
	SZ_VLONG,	/* [TUVLONG] */
	SZ_FLOAT,	/* [TFLOAT] */
	SZ_DOUBLE,	/* [TDOUBLE] */
	SZ_IND,		/* [TIND] */
	0,		/* [TFUNC] */
	-1,		/* [TARRAY] */
	0,		/* [TVOID] */
	-1,		/* [TSTRUCT] */
	-1,		/* [TUNION] */
	SZ_INT,		/* [TENUM] */
};
long	ncast[NTYPE] =
{
	0,				/* [TXXX] */
	BCHAR|BUCHAR,			/* [TCHAR] */
	BCHAR|BUCHAR,			/* [TUCHAR] */
	BSHORT|BUSHORT,			/* [TSHORT] */
	BSHORT|BUSHORT,			/* [TUSHORT] */
	BINT|BUINT|BLONG|BULONG|BIND,	/* [TINT] */
	BINT|BUINT|BLONG|BULONG|BIND,	/* [TUINT] */
	BINT|BUINT|BLONG|BULONG|BIND,	/* [TLONG] */
	BINT|BUINT|BLONG|BULONG|BIND,	/* [TULONG] */
	BVLONG|BUVLONG,			/* [TVLONG] */
	BVLONG|BUVLONG,			/* [TUVLONG] */
	BFLOAT,				/* [TFLOAT] */
	BDOUBLE,			/* [TDOUBLE] */
	BLONG|BULONG|BIND,		/* [TIND] */
	0,				/* [TFUNC] */
	0,				/* [TARRAY] */
	0,				/* [TVOID] */
	BSTRUCT,			/* [TSTRUCT] */
	BUNION,				/* [TUNION] */
	0,				/* [TENUM] */
};