com.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(tcompat(n, T, l->type, tindir))
			goto bad;
		n->type = l->type->link;
		n->addable = 1;
		break;

	case OSTRUCT:
		if(tcomx(n))
			goto bad;
		break;
	}
	t = n->type;
	if(t == T)
		goto bad;
	if(t->width < 0) {
		snap(t);
		if(t->width < 0) {
			if(typesu[t->etype] && t->tag)
				diag(n, "structure not fully declared %s", t->tag->name);
			else
				diag(n, "structure not fully declared");
			goto bad;
		}
	}
	if(typeaf[t->etype]) {
		if(f & ADDROF)
			goto addaddr;
		if(f & ADDROP)
			warn(n, "address of array/func ignored");
	}
	return 0;

addaddr:
	if(tlvalue(n))
		goto bad;
	l = new1(OXXX, Z, Z);
	*l = *n;
	n->op = OADDR;
	if(l->type->etype == TARRAY)
		l->type = l->type->link;
	n->left = l;
	n->right = Z;
	n->addable = 0;
	n->type = typ(TIND, l->type);
	n->type->width = types[TIND]->width;
	return 0;

bad:
	n->type = T;
	return 1;
}

int
tcoma(Node *l, Node *n, Type *t, int f)
{
	Node *n1;
	int o;

	if(t != T)
	if(t->etype == TOLD || t->etype == TDOT)	/* .../old in prototype */
		t = T;
	if(n == Z) {
		if(t != T && !sametype(t, types[TVOID])) {
			diag(n, "not enough function arguments: %F", l);
			return 1;
		}
		return 0;
	}
	if(n->op == OLIST) {
		o = tcoma(l, n->left, t, 0);
		if(t != T) {
			t = t->down;
			if(t == T)
				t = types[TVOID];
		}
		return o | tcoma(l, n->right, t, 1);
	}
	if(f && t != T)
		tcoma(l, Z, t->down, 0);
	if(tcom(n) || tcompat(n, T, n->type, targ))
		return 1;
	if(sametype(t, types[TVOID])) {
		diag(n, "too many function arguments: %F", l);
		return 1;
	}
	if(t != T) {
		typeext(t, n);
		if(stcompat(nodproto, t, n->type, tasign)) {
			diag(l, "argument prototype mismatch \"%T\" for \"%T\": %F",
				n->type, t, l);
			return 1;
		}
		switch(t->etype) {
		case TCHAR:
		case TSHORT:
			t = types[TINT];
			break;

		case TUCHAR:
		case TUSHORT:
			t = types[TUINT];
			break;
		}
	} else
	switch(n->type->etype)
	{
	case TCHAR:
	case TSHORT:
		t = types[TINT];
		break;

	case TUCHAR:
	case TUSHORT:
		t = types[TUINT];
		break;

	case TFLOAT:
		t = types[TDOUBLE];
	}
	if(t != T && !sametype(t, n->type)) {
		n1 = new1(OXXX, Z, Z);
		*n1 = *n;
		n->op = OCAST;
		n->left = n1;
		n->right = Z;
		n->type = t;
		n->addable = 0;
	}
	return 0;
}

int
tcomd(Node *n)
{
	Type *t;
	long o;

	o = 0;
	t = dotsearch(n->sym, n->left->type->link, n, &o);
	if(t == T) {
		diag(n, "not a member of struct/union: %F", n);
		return 1;
	}
	makedot(n, t, o);
	return 0;
}

int
tcomx(Node *n)
{
	Type *t;
	Node *l, *r, **ar, **al;
	int e;

	e = 0;
	if(n->type->etype != TSTRUCT) {
		diag(n, "constructor must be a structure");
		return 1;
	}
	l = invert(n->left);
	n->left = l;
	al = &n->left;
	for(t = n->type->link; t != T; t = t->down) {
		if(l == Z) {
			diag(n, "constructor list too short");
			return 1;
		}
		if(l->op == OLIST) {
			r = l->left;
			ar = &l->left;
			al = &l->right;
			l = l->right;
		} else {
			r = l;
			ar = al;
			l = Z;
		}
		if(tcom(r))
			e++;
		typeext(t, r);
		if(tcompat(n, t, r->type, tasign))
			e++;
		constas(n, t, r->type);
		if(!e && !sametype(t, r->type)) {
			r = new1(OCAST, r, Z);
			r->type = t;
			*ar = r;
		}
	}
	if(l != Z) {
		diag(n, "constructor list too long");
		return 1;
	}
	return e;
}

int
tlvalue(Node *n)
{

	if(!n->addable) {
		diag(n, "not an l-value");
		return 1;
	}
	return 0;
}

/*
 *	general rewrite
 *	(IND(ADDR x)) ==> x
 *	(ADDR(IND x)) ==> x
 *	remove some zero operands
 *	remove no op casts
 *	evaluate constants
 */
void
ccom(Node *n)
{
	Node *l, *r;
	int t;

loop:
	if(n == Z)
		return;
	l = n->left;
	r = n->right;
	switch(n->op) {

	case OAS:
	case OASXOR:
	case OASAND:
	case OASOR:
	case OASMOD:
	case OASLMOD:
	case OASLSHR:
	case OASASHR:
	case OASASHL:
	case OASDIV:
	case OASLDIV:
	case OASMUL:
	case OASLMUL:
	case OASSUB:
	case OASADD:
		ccom(l);
		ccom(r);
		if(n->op == OASLSHR || n->op == OASASHR || n->op == OASASHL)
		if(r->op == OCONST) {
			t = n->type->width * 8;	/* bits per byte */
			if(r->vconst >= t || r->vconst < 0)
				warn(n, "stupid shift: %lld", r->vconst);
		}
		break;

	case OCAST:
		ccom(l);
		if(l->op == OCONST) {
			evconst(n);
			if(n->op == OCONST)
				break;
		}
		if(nocast(l->type, n->type)) {
			l->type = n->type;
			*n = *l;
		}
		break;

	case OCOND:
		ccom(l);
		ccom(r);
		if(l->op == OCONST)
			if(vconst(l) == 0)
				*n = *r->right;
			else
				*n = *r->left;
		break;

	case OREGISTER:
	case OINDREG:
	case OCONST:
	case ONAME:
		break;

	case OADDR:
		ccom(l);
		l->etype = TVOID;
		if(l->op == OIND) {
			l->left->type = n->type;
			*n = *l->left;
			break;
		}
		goto common;

	case OIND:
		ccom(l);
		if(l->op == OADDR) {
			l->left->type = n->type;
			*n = *l->left;
			break;
		}
		goto common;

	case OEQ:
	case ONE:

	case OLE:
	case OGE:
	case OLT:
	case OGT:

	case OLS:
	case OHS:
	case OLO:
	case OHI:
		ccom(l);
		ccom(r);
		if(compar(n, 0) || compar(n, 1))
			break;
		relcon(l, r);
		relcon(r, l);
		goto common;

	case OASHR:
	case OASHL:
	case OLSHR:
		ccom(l);
		if(vconst(l) == 0 && !side(r)) {
			*n = *l;
			break;
		}
		ccom(r);
		if(vconst(r) == 0) {
			*n = *l;
			break;
		}
		if(r->op == OCONST) {
			t = n->type->width * 8;	/* bits per byte */
			if(r->vconst >= t || r->vconst <= -t)
				warn(n, "stupid shift: %lld", r->vconst);
		}
		goto common;

	case OMUL:
	case OLMUL:
		ccom(l);
		t = vconst(l);
		if(t == 0 && !side(r)) {
			*n = *l;
			break;
		}
		if(t == 1) {
			*n = *r;
			goto loop;
		}
		ccom(r);
		t = vconst(r);
		if(t == 0 && !side(l)) {
			*n = *r;
			break;
		}
		if(t == 1) {
			*n = *l;
			break;
		}
		goto common;

	case ODIV:
	case OLDIV:
		ccom(l);
		if(vconst(l) == 0 && !side(r)) {
			*n = *l;
			break;
		}
		ccom(r);
		t = vconst(r);
		if(t == 0) {
			diag(n, "divide check");
			*n = *r;
			break;
		}
		if(t == 1) {
			*n = *l;
			break;
		}
		goto common;

	case OSUB:
		ccom(r);
		if(r->op == OCONST) {
			if(typefd[r->type->etype]) {
				n->op = OADD;
				r->fconst = -r->fconst;
				goto loop;
			} else {
				n->op = OADD;
				r->vconst = -r->vconst;
				goto loop;
			}
		}
		ccom(l);
		goto common;

	case OXOR:
	case OOR:
	case OADD:
		ccom(l);
		if(vconst(l) == 0) {
			*n = *r;
			goto loop;
		}
		ccom(r);
		if(vconst(r) == 0) {
			*n = *l;
			break;
		}
		goto commute;

	case OAND:
		ccom(l);
		ccom(r);
		if(vconst(l) == 0 && !side(r)) {
			*n = *l;
			break;
		}
		if(vconst(r) == 0 && !side(l)) {
			*n = *r;
			break;
		}

	commute:
		/* look for commutative constant */
		if(r->op == OCONST) {
			if(l->op == n->op) {
				if(l->left->op == OCONST) {
					n->right = l->right;
					l->right = r;
					goto loop;
				}
				if(l->right->op == OCONST) {
					n->right = l->left;
					l->left = r;
					goto loop;
				}
			}
		}
		if(l->op == OCONST) {
			if(r->op == n->op) {
				if(r->left->op == OCONST) {
					n->left = r->right;
					r->right = l;
					goto loop;
				}
				if(r->right->op == OCONST) {
					n->left = r->left;
					r->left = l;
					goto loop;
				}
			}
		}
		goto common;

	case OANDAND:
		ccom(l);
		if(vconst(l) == 0) {
			*n = *l;
			break;
		}
		ccom(r);
		goto common;

	case OOROR:
		ccom(l);
		if(l->op == OCONST && l->vconst != 0) {
			*n = *l;
			n->vconst = 1;
			break;
		}
		ccom(r);
		goto common;

	default:
		if(l != Z)
			ccom(l);
		if(r != Z)
			ccom(r);
	common:
		if(l != Z)
		if(l->op != OCONST)
			break;
		if(r != Z)
		if(r->op != OCONST)
			break;
		evconst(n);
	}
}

/*	OEQ, ONE, OLE, OLS, OLT, OLO, OGE, OHS, OGT, OHI */
static char *cmps[12] = 
{
	"==", "!=", "<=", "<=", "<", "<", ">=", ">=", ">", ">",
};

/* 128-bit numbers */
typedef struct Big Big;
struct Big
{
	vlong a;
	uvlong b;
};
static int
cmp(Big x, Big y)
{
	if(x.a != y.a){
		if(x.a < y.a)
			return -1;
		return 1;
	}
	if(x.b != y.b){
		if(x.b < y.b)
			return -1;
		return 1;
	}
	return 0;
}
static Big
add(Big x, int y)
{
	uvlong ob;
	
	ob = x.b;
	x.b += y;
	if(y > 0 && x.b < ob)
		x.a++;
	if(y < 0 && x.b > ob)
		x.a--;
	return x;
} 

Big
big(vlong a, uvlong b)
{
	Big x;

	x.a = a;
	x.b = b;
	return x;
}

int
compar(Node *n, int reverse)
{
	Big lo, hi, x;
	int op;
	char xbuf[40], cmpbuf[50];
	Node *l, *r;
	Type *lt, *rt;

	/*
	 * The point of this function is to diagnose comparisons 
	 * that can never be true or that look misleading because
	 * of the `usual arithmetic conversions'.  As an example 
	 * of the latter, if x is a ulong, then if(x <= -1) really means
	 * if(x <= 0xFFFFFFFF), while if(x <= -1LL) really means
	 * what it says (but 8c compiles it wrong anyway).
	 */

	if(reverse){
		r = n->left;
		l = n->right;
		op = comrel[relindex(n->op)];
	}else{
		l = n->left;
		r = n->right;
		op = n->op;
	}

	/*
	 * Skip over left casts to find out the original expression range.
	 */
	while(l->op == OCAST)
		l = l->left;
	if(l->op == OCONST)
		return 0;
	lt = l->type;
	if(l->op == ONAME){
		lt = l->sym->type;
		if(lt && lt->etype == TARRAY)
			lt = lt->link;
	}
	if(lt == T)
		return 0;
	if(lt->etype == TXXX || lt->etype > TUVLONG)
		return 0;
	
	/*
	 * Skip over the right casts to find the on-screen value.
	 */
	if(r->op != OCONST)
		return 0;
	while(r->oldop == OCAST && !r->xcast)
		r = r->left;
	rt = r->type;
	if(rt == T)
		return 0;

	x.b = r->vconst;
	x.a = 0;
	if((rt->etype&1) && r->vconst < 0)	/* signed negative */
		x.a = ~0ULL;

	if((lt->etype&1)==0){
		/* unsigned */
		lo = big(0, 0);
		if(lt->width == 8)
			hi = big(0, ~0ULL);
		else
			hi = big(0, (1LL<<(l->type->width*8))-1);
	}else{
		lo = big(~0ULL, -(1LL<<(l->type->width*8-1)));
		hi = big(0, (1LL<<(l->type->width*8-1))-1);
	}

	switch(op){
	case OLT:
	case OLO:
	case OGE:
	case OHS:
		if(cmp(x, lo) <= 0)
			goto useless;
		if(cmp(x, add(hi, 1)) >= 0)
			goto useless;
		break;
	case OLE:
	case OLS:
	case OGT:
	case OHI:
		if(cmp(x, add(lo, -1)) <= 0)
			goto useless;
		if(cmp(x, hi) >= 0)
			goto useless;
		break;
	case OEQ:
	case ONE:
		/*
		 * Don't warn about comparisons if the expression
		 * is as wide as the value: the compiler-supplied casts
		 * will make both outcomes possible.
		 */
		if(lt->width >= rt->width && debug['w'] < 2)
			return 0;
		if(cmp(x, lo) < 0 || cmp(x, hi) > 0)
			goto useless;
		break;
	}
	return 0;

useless:
	if((x.a==0 && x.b<=9) || (x.a==~0LL && x.b >= -9ULL))
		snprint(xbuf, sizeof xbuf, "%lld", x.b);
	else if(x.a == 0)
		snprint(xbuf, sizeof xbuf, "%#llux", x.b);
	else
		snprint(xbuf, sizeof xbuf, "%#llx", x.b);
	if(reverse)
		snprint(cmpbuf, sizeof cmpbuf, "%s %s %T",
			xbuf, cmps[relindex(n->op)], lt);
	else
		snprint(cmpbuf, sizeof cmpbuf, "%T %s %s",
			lt, cmps[relindex(n->op)], xbuf);
	warn(n, "useless or misleading comparison: %s", cmpbuf);
	return 0;
}