src/gen.c - master - ifl/lcc

src/gen.c
829 строк21 KB
David R. Hanson
Fix issue 8 reported by Martin Ettl.
05 ноя 2014, 03:55
05 ноя 2014, 03:5557047a2
#include "c.h"

static char rcsid[] = "$Id$";

#define readsreg(p) \
	(generic((p)->op)==INDIR && (p)->kids[0]->op==VREG+P)
#define setsrc(d) ((d) && (d)->x.regnode && \
	(d)->x.regnode->set == src->x.regnode->set && \
	(d)->x.regnode->mask&src->x.regnode->mask)

#define relink(a, b) ((b)->x.prev = (a), (a)->x.next = (b))

static Symbol   askfixedreg(Symbol);
static Symbol   askreg(Symbol, unsigned*);
static void     blkunroll(int, int, int, int, int, int, int[]);
static void     docall(Node);
static void     dumpcover(Node, int, int);
static void     dumpregs(char *, char *, char *);
static void     dumprule(int);
static void     dumptree(Node);
static void     genreload(Node, Symbol, int);
static void     genspill(Symbol, Node, Symbol);
static Symbol   getreg(Symbol, unsigned*, Node);
static int      getrule(Node, int);
static void     linearize(Node, Node);
static int      moveself(Node);
static void     prelabel(Node);
static Node*    prune(Node, Node*);
static void     putreg(Symbol);
static void     ralloc(Node);
static void     reduce(Node, int);
static int      reprune(Node*, int, int, Node);
static int      requate(Node);
static Node     reuse(Node, int);
static void     rewrite(Node);
static Symbol   spillee(Symbol, unsigned mask[], Node);
static void     spillr(Symbol, Node);
static int      uses(Node, Regnode);

int offset;

int maxoffset;

int framesize;
int argoffset;

int maxargoffset;

int dalign, salign;
int bflag = 0;  /* omit */
int dflag = 0;

int swap;

unsigned (*emitter)(Node, int) = emitasm;
static char NeedsReg[] = {
	0,                      /* unused */
	1,                      /* CNST */
	0, 0,                   /* ARG ASGN */
	1,                      /* INDIR  */
	0, 0, 1, 1,             /*  -  - CVF CVI */
	1, 0, 1, 1,             /* CVP - CVU NEG */
	1,                      /* CALL */
	1,                      /* LOAD */
	0,                      /* RET */
	1, 1, 1,                /* ADDRG ADDRF ADDRL */
	1, 1, 1, 1, 1,          /* ADD SUB LSH MOD RSH */
	1, 1, 1, 1,             /* BAND BCOM BOR BXOR */
	1, 1,                   /* DIV MUL */
	0, 0, 0, 0, 0, 0,       /* EQ GE GT LE LT NE */
	0, 0                   /* JUMP LABEL   */
};
Node head;

unsigned freemask[2];
unsigned usedmask[2];
unsigned tmask[2];
unsigned vmask[2];
Symbol mkreg(char *fmt, int n, int mask, int set) {
	Symbol p;

	NEW0(p, PERM);
	p->name = p->x.name = stringf(fmt, n);
	NEW0(p->x.regnode, PERM);
	p->x.regnode->number = n;
	p->x.regnode->mask = mask<<n;
	p->x.regnode->set = set;
	return p;
}
Symbol mkwildcard(Symbol *syms) {
	Symbol p;

	NEW0(p, PERM);
	p->name = p->x.name = "wildcard";
	p->x.wildcard = syms;
	return p;
}
void mkauto(Symbol p) {
	assert(p->sclass == AUTO);
	offset = roundup(offset + p->type->size, p->type->align);
	p->x.offset = -offset;
	p->x.name = stringd(-offset);
}
void blockbeg(Env *e) {
	e->offset = offset;
	e->freemask[IREG] = freemask[IREG];
	e->freemask[FREG] = freemask[FREG];
}
void blockend(Env *e) {
	if (offset > maxoffset)
		maxoffset = offset;
	offset = e->offset;
	freemask[IREG] = e->freemask[IREG];
	freemask[FREG] = e->freemask[FREG];
}
int mkactual(int align, int size) {
	int n = roundup(argoffset, align);

	argoffset = n + size;
	return n;
}
static void docall(Node p) {
	p->syms[1] = p->syms[0];
	p->syms[0] = intconst(argoffset);
	if (argoffset > maxargoffset)
		maxargoffset = argoffset;
	argoffset = 0;
}
void blkcopy(int dreg, int doff, int sreg, int soff, int size, int tmp[]) {
	assert(size >= 0);
	if (size == 0)
		return;
	else if (size <= 2)
		blkunroll(size, dreg, doff, sreg, soff, size, tmp);
	else if (size == 3) {
		blkunroll(2, dreg, doff,   sreg, soff,   2, tmp);
		blkunroll(1, dreg, doff+2, sreg, soff+2, 1, tmp);
	}
	else if (size <= 16) {
		blkunroll(4, dreg, doff, sreg, soff, size&~3, tmp);
		blkcopy(dreg, doff+(size&~3),
	                sreg, soff+(size&~3), size&3, tmp);
	}
	else
		(*IR->x.blkloop)(dreg, doff, sreg, soff, size, tmp);
}
static void blkunroll(int k, int dreg, int doff, int sreg, int soff, int size, int tmp[]) {
	int i;

	assert(IR->x.max_unaligned_load);
	if (k > IR->x.max_unaligned_load
	&& (k > salign || k > dalign))
		k = IR->x.max_unaligned_load;
	for (i = 0; i+k < size; i += 2*k) {
		(*IR->x.blkfetch)(k, soff+i,   sreg, tmp[0]);
		(*IR->x.blkfetch)(k, soff+i+k, sreg, tmp[1]);
		(*IR->x.blkstore)(k, doff+i,   dreg, tmp[0]);
		(*IR->x.blkstore)(k, doff+i+k, dreg, tmp[1]);
	}
	if (i < size) {
		(*IR->x.blkfetch)(k, i+soff, sreg, tmp[0]);
		(*IR->x.blkstore)(k, i+doff, dreg, tmp[0]);
	}
}
void parseflags(int argc, char *argv[]) {
	int i;

	for (i = 0; i < argc; i++)
		if (strcmp(argv[i], "-d") == 0)
			dflag = 1;
		else if (strcmp(argv[i], "-b") == 0)	/* omit */
			bflag = 1;			/* omit */
}
static int getrule(Node p, int nt) {
	int rulenum;

	assert(p);
	rulenum = (*IR->x._rule)(p->x.state, nt);
	if (!rulenum) {
		fprint(stderr, "(%x->op=%s at %w is corrupt.)\n", p, opname(p->op), &src);
		assert(0);
	}
	return rulenum;
}
static void reduce(Node p, int nt) {
	int rulenum, i;
	short *nts;
	Node kids[10];

	p = reuse(p, nt);
	rulenum = getrule(p, nt);
	nts = IR->x._nts[rulenum];
	(*IR->x._kids)(p, rulenum, kids);
	for (i = 0; nts[i]; i++)
		reduce(kids[i], nts[i]);
	if (IR->x._isinstruction[rulenum]) {
		assert(p->x.inst == 0 || p->x.inst == nt);
		p->x.inst = nt;
		if (p->syms[RX] && p->syms[RX]->temporary) {
			debug(fprint(stderr, "(using %s)\n", p->syms[RX]->name));
			p->syms[RX]->x.usecount++;
		}
	}
}
static Node reuse(Node p, int nt) {
	struct _state {
		short cost[1];
	};
	Symbol r = p->syms[RX];

	if (generic(p->op) == INDIR && p->kids[0]->op == VREG+P
	&& r->u.t.cse && p->x.mayrecalc
	&& ((struct _state*)r->u.t.cse->x.state)->cost[nt] == 0)
		return r->u.t.cse;
	else
		return p;
}

int mayrecalc(Node p) {
	int op;

	assert(p && p->syms[RX]);
	if (p->syms[RX]->u.t.cse == NULL)
		return 0;
	op = generic(p->syms[RX]->u.t.cse->op);
	if (op == CNST || op == ADDRF || op == ADDRG || op == ADDRL) {
		p->x.mayrecalc = 1;
		return 1;
	} else
		return 0;
}
static Node *prune(Node p, Node pp[]) {
	if (p == NULL)
		return pp;
	p->x.kids[0] = p->x.kids[1] = p->x.kids[2] = NULL;
	if (p->x.inst == 0)
		return prune(p->kids[1], prune(p->kids[0], pp));
	else if (p->syms[RX] && p->syms[RX]->temporary
	&& p->syms[RX]->x.usecount < 2) {
		p->x.inst = 0;
		debug(fprint(stderr, "(clobbering %s)\n", p->syms[RX]->name));
		return prune(p->kids[1], prune(p->kids[0], pp));
	}
	else {
		prune(p->kids[1], prune(p->kids[0], &p->x.kids[0]));
		*pp = p;
		return pp + 1;
	}
}

#define ck(i) return (i) ? 0 : LBURG_MAX

int range(Node p, int lo, int hi) {
	Symbol s = p->syms[0];

	switch (specific(p->op)) {
	case ADDRF+P:
	case ADDRL+P: ck(s->x.offset >= lo && s->x.offset <= hi);
	case CNST+I:  ck(s->u.c.v.i  >= lo && s->u.c.v.i  <= hi);
	case CNST+U:  ck(s->u.c.v.u  >= lo && s->u.c.v.u  <= hi);
	case CNST+P:  ck(s->u.c.v.p  == 0  && lo <= 0 && hi >= 0);
	}
	return LBURG_MAX;
}
static void dumptree(Node p) {
	if (p->op == VREG+P && p->syms[0]) {
		fprint(stderr, "VREGP(%s)", p->syms[0]->name);
		return;
	} else if (generic(p->op) == LOAD) {
		fprint(stderr, "LOAD(");
		dumptree(p->kids[0]);
		fprint(stderr, ")");
		return;
	}
	fprint(stderr, "%s(", opname(p->op));
	switch (generic(p->op)) {
	case CNST: case LABEL:
	case ADDRG: case ADDRF: case ADDRL:
		if (p->syms[0])
			fprint(stderr, "%s", p->syms[0]->name);
		break;
	case RET:
		if (p->kids[0])
			dumptree(p->kids[0]);
		break;
	case CVF: case CVI: case CVP: case CVU: case JUMP: 
	case ARG: case BCOM: case NEG: case INDIR:
		dumptree(p->kids[0]);
		break;
	case CALL:
		if (optype(p->op) != B) {
			dumptree(p->kids[0]);
			break;
		}
		/* else fall thru */
	case EQ: case NE: case GT: case GE: case LE: case LT:
	case ASGN: case BOR: case BAND: case BXOR: case RSH: case LSH:
	case ADD: case SUB:  case DIV: case MUL: case MOD:
		dumptree(p->kids[0]);
		fprint(stderr, ", ");
		dumptree(p->kids[1]);
		break;
	default: assert(0);
	}
	fprint(stderr, ")");
}
static void dumpcover(Node p, int nt, int in) {
	int rulenum, i;
	short *nts;
	Node kids[10];

	p = reuse(p, nt);
	rulenum = getrule(p, nt);
	nts = IR->x._nts[rulenum];
	fprint(stderr, "dumpcover(%x) = ", p);
	for (i = 0; i < in; i++)
		fprint(stderr, " ");
	dumprule(rulenum);
	(*IR->x._kids)(p, rulenum, kids);
	for (i = 0; nts[i]; i++)
		dumpcover(kids[i], nts[i], in+1);
}

static void dumprule(int rulenum) {
	assert(rulenum);
	fprint(stderr, "%s / %s", IR->x._string[rulenum],
		IR->x._templates[rulenum]);
	if (!IR->x._isinstruction[rulenum])
		fprint(stderr, "\n");
}
unsigned emitasm(Node p, int nt) {
	int rulenum;
	short *nts;
	char *fmt;
	Node kids[10];

	p = reuse(p, nt);
	rulenum = getrule(p, nt);
	nts = IR->x._nts[rulenum];
	fmt = IR->x._templates[rulenum];
	assert(fmt);
	if (IR->x._isinstruction[rulenum] && p->x.emitted)
		print("%s", p->syms[RX]->x.name);
	else if (*fmt == '#')
		(*IR->x.emit2)(p);
	else {
		if (*fmt == '?') {
			fmt++;
			assert(p->kids[0]);
			if (p->syms[RX] == p->x.kids[0]->syms[RX])
				while (*fmt++ != '\n')
					;
		}
		for ((*IR->x._kids)(p, rulenum, kids); *fmt; fmt++)
			if (*fmt != '%')
				(void)putchar(*fmt);
			else if (*++fmt == 'F')
				print("%d", framesize);
			else if (*fmt >= '0' && *fmt <= '9')
				emitasm(kids[*fmt - '0'], nts[*fmt - '0']);
			else if (*fmt >= 'a' && *fmt < 'a' + NELEMS(p->syms))
				fputs(p->syms[*fmt - 'a']->x.name, stdout);
			else
				(void)putchar(*fmt);
	}
	return 0;
}
void emit(Node p) {
	for (; p; p = p->x.next) {
		assert(p->x.registered);
		if (p->x.equatable && requate(p) || moveself(p))
			;
		else
			(*emitter)(p, p->x.inst);
		p->x.emitted = 1;
	}
}
static int moveself(Node p) {
	return p->x.copy
	&& p->syms[RX]->x.name == p->x.kids[0]->syms[RX]->x.name;
}
int move(Node p) {
	p->x.copy = 1;
	return 1;
}
static int requate(Node q) {
	Symbol src = q->x.kids[0]->syms[RX];
	Symbol tmp = q->syms[RX];
	Node p;
	int n = 0;

	debug(fprint(stderr, "(requate(%x): tmp=%s src=%s)\n", q, tmp->x.name, src->x.name));
	for (p = q->x.next; p; p = p->x.next)
		if (p->x.copy && p->syms[RX] == src
		&&  p->x.kids[0]->syms[RX] == tmp)
			debug(fprint(stderr, "(requate arm 0 at %x)\n", p)),
			p->syms[RX] = tmp;
		else if (setsrc(p->syms[RX]) && !moveself(p) && !readsreg(p))
			return 0;
		else if (p->x.spills)
			return 0;
		else if (generic(p->op) == CALL && p->x.next)
			return 0;
		else if (p->op == LABEL+V && p->x.next)
			return 0;
		else if (p->syms[RX] == tmp && readsreg(p))
			debug(fprint(stderr, "(requate arm 5 at %x)\n", p)),
			n++;
		else if (p->syms[RX] == tmp)
			break;
	debug(fprint(stderr, "(requate arm 7 at %x)\n", p));
	assert(n > 0);
	for (p = q->x.next; p; p = p->x.next)
		if (p->syms[RX] == tmp && readsreg(p)) {
			p->syms[RX] = src;
			if (--n <= 0)
				break;
		}
	return 1;
}
static void prelabel(Node p) {
	if (p == NULL)
		return;
	prelabel(p->kids[0]);
	prelabel(p->kids[1]);
	if (NeedsReg[opindex(p->op)])
		setreg(p, (*IR->x.rmap)(opkind(p->op)));
	switch (generic(p->op)) {
	case ADDRF: case ADDRL:
		if (p->syms[0]->sclass == REGISTER)
			p->op = VREG+P;
		break;
	case INDIR:
		if (p->kids[0]->op == VREG+P)
			setreg(p, p->kids[0]->syms[0]);
		break;
	case ASGN:
		if (p->kids[0]->op == VREG+P)
			rtarget(p, 1, p->kids[0]->syms[0]);
		break;
	case CVI: case CVU: case CVP:
		if (optype(p->op) != F
		&&  opsize(p->op) <= p->syms[0]->u.c.v.i)
			p->op = LOAD + opkind(p->op);
		break;
	}
	(IR->x.target)(p);
}
void setreg(Node p, Symbol r) {
	p->syms[RX] = r;
}
void rtarget(Node p, int n, Symbol r) {
	Node q = p->kids[n];

	assert(q);
	assert(r);
	assert(r->sclass == REGISTER || !r->x.wildcard);
	assert(q->syms[RX]);
	if (r != q->syms[RX] && !q->syms[RX]->x.wildcard) {
		q = newnode(LOAD + opkind(q->op),
			q, NULL, q->syms[0]);
		if (r->u.t.cse == p->kids[n])
			r->u.t.cse = q;
		p->kids[n] = p->x.kids[n] = q;
		q->x.kids[0] = q->kids[0];
	}
	setreg(q, r);
	debug(fprint(stderr, "(targeting %x->x.kids[%d]=%x to %s)\n", p, n, p->kids[n], r->x.name));
}
static void rewrite(Node p) {
	assert(p->x.inst == 0);
	prelabel(p);
	debug(dumptree(p));
	debug(fprint(stderr, "\n"));
	(*IR->x._label)(p);
	debug(dumpcover(p, 1, 0));
	reduce(p, 1);
}
Node gen(Node forest) {
	int i;
	struct node sentinel;
	Node dummy, p;

	head = forest;
	for (p = forest; p; p = p->link) {
		assert(p->count == 0);
		if (generic(p->op) == CALL)
			docall(p);
		else if (   generic(p->op) == ASGN
		&& generic(p->kids[1]->op) == CALL)
			docall(p->kids[1]);
		else if (generic(p->op) == ARG)
			(*IR->x.doarg)(p);
		rewrite(p);
		p->x.listed = 1;
	}
	for (p = forest; p; p = p->link)
		prune(p, &dummy);
	relink(&sentinel, &sentinel);
	for (p = forest; p; p = p->link)
		linearize(p, &sentinel);
	forest = sentinel.x.next;
	assert(forest);
	sentinel.x.next->x.prev = NULL;
	sentinel.x.prev->x.next = NULL;
	for (p = forest; p; p = p->x.next)
		for (i = 0; i < NELEMS(p->x.kids) && p->x.kids[i]; i++) {
			assert(p->x.kids[i]->syms[RX]);
			if (p->x.kids[i]->syms[RX]->temporary) {
				p->x.kids[i]->x.prevuse =
					p->x.kids[i]->syms[RX]->x.lastuse;
				p->x.kids[i]->syms[RX]->x.lastuse = p->x.kids[i];
			}
		}
	for (p = forest; p; p = p->x.next) {
		ralloc(p);
		if (p->x.listed && NeedsReg[opindex(p->op)]
		&& (*IR->x.rmap)(opkind(p->op))) {
			assert(generic(p->op) == CALL || generic(p->op) == LOAD);
			putreg(p->syms[RX]);
		}
	}
	return forest;
}
int notarget(Node p) {
	return p->syms[RX]->x.wildcard ? 0 : LBURG_MAX;
}
static void putreg(Symbol r) {
	assert(r && r->x.regnode);
	freemask[r->x.regnode->set] |= r->x.regnode->mask;
	debug(dumpregs("(freeing %s)\n", r->x.name, NULL));
}
static Symbol askfixedreg(Symbol s) {
	Regnode r = s->x.regnode;
	int n = r->set;

	if (r->mask&~freemask[n])
		return NULL;
	else {
		freemask[n] &= ~r->mask;
		usedmask[n] |=  r->mask;
		return s;
	}
}
static Symbol askreg(Symbol rs, unsigned rmask[]) {
	int i;

	if (rs->x.wildcard == NULL)
		return askfixedreg(rs);
	for (i = 31; i >= 0; i--) {
		Symbol r = rs->x.wildcard[i];
		if (r != NULL
		&& !(r->x.regnode->mask&~rmask[r->x.regnode->set])
		&& askfixedreg(r))
			return r;
	}
	return NULL;
}

static Symbol getreg(Symbol s, unsigned mask[], Node p) {
	Symbol r = askreg(s, mask);
	if (r == NULL) {
		r = spillee(s, mask, p);
		assert(r && r->x.regnode);
		spill(r->x.regnode->mask, r->x.regnode->set, p);
		r = askreg(s, mask);
	}
	assert(r && r->x.regnode);
	r->x.regnode->vbl = NULL;
	return r;
}
int askregvar(Symbol p, Symbol regs) {
	Symbol r;

	assert(p);
	if (p->sclass != REGISTER)
		return 0;
	else if (!isscalar(p->type)) {
		p->sclass = AUTO;
		return 0;
	}
	else if (p->temporary) {
		p->x.name = "?";
		return 1;
	}
	else if ((r = askreg(regs, vmask)) != NULL) {
		p->x.regnode = r->x.regnode;
		p->x.regnode->vbl = p;
		p->x.name = r->x.name;
		debug(dumpregs("(allocating %s to symbol %s)\n", p->x.name, p->name));
		return 1;
	}
	else {
		p->sclass = AUTO;
		return 0;
	}
}
static void linearize(Node p, Node next) {
	int i;

	for (i = 0; i < NELEMS(p->x.kids) && p->x.kids[i]; i++)
		linearize(p->x.kids[i], next);
	relink(next->x.prev, p);
	relink(p, next);
	debug(fprint(stderr, "(listing %x)\n", p));
}
static void ralloc(Node p) {
	int i;
	unsigned mask[2];

	mask[0] = tmask[0];
	mask[1] = tmask[1];
	assert(p);
	debug(fprint(stderr, "(rallocing %x)\n", p));
	for (i = 0; i < NELEMS(p->x.kids) && p->x.kids[i]; i++) {
		Node kid = p->x.kids[i];
		Symbol r = kid->syms[RX];
		assert(r && kid->x.registered);
		if (r->sclass != REGISTER && r->x.lastuse == kid)
			putreg(r);
	}
	if (!p->x.registered && NeedsReg[opindex(p->op)]
	&& (*IR->x.rmap)(opkind(p->op))) {
		Symbol sym = p->syms[RX], set = sym;
		assert(sym);
		if (sym->temporary)
			set = (*IR->x.rmap)(opkind(p->op));
		assert(set);
		if (set->sclass != REGISTER) {
			Symbol r;
			if (*IR->x._templates[getrule(p, p->x.inst)] == '?')
				for (i = 1; i < NELEMS(p->x.kids) && p->x.kids[i]; i++) {
					Symbol r = p->x.kids[i]->syms[RX];
					assert(p->x.kids[i]->x.registered);
					assert(r && r->x.regnode);
					assert(sym->x.wildcard || sym != r);
					mask[r->x.regnode->set] &= ~r->x.regnode->mask;
				}
			r = getreg(set, mask, p);
			if (sym->temporary) {
				Node q;
				r->x.lastuse = sym->x.lastuse;
				for (q = sym->x.lastuse; q; q = q->x.prevuse) {
					q->syms[RX] = r;
					q->x.registered = 1;
					if (sym->u.t.cse && q->x.copy)
						q->x.equatable = 1;
				}
			} else {
				p->syms[RX] = r;
				r->x.lastuse = p;
			}
			debug(dumpregs("(allocating %s to node %x)\n", r->x.name, (char *) p));
		}
	}
	p->x.registered = 1;
	(*IR->x.clobber)(p);
}
static Symbol spillee(Symbol set, unsigned mask[], Node here) {
	Symbol bestreg = NULL;
	int bestdist = -1, i;

	assert(set);
	if (!set->x.wildcard)
		bestreg = set;
	else {
		for (i = 31; i >= 0; i--) {
			Symbol ri = set->x.wildcard[i];
			if (
				ri != NULL &&
				ri->x.lastuse &&
				(ri->x.regnode->mask&tmask[ri->x.regnode->set]&mask[ri->x.regnode->set])
			) {
				Regnode rn = ri->x.regnode;
				Node q = here;
				int dist = 0;
				for (; q && !uses(q, rn); q = q->x.next)
					dist++;
				if (q && dist > bestdist) {
					bestdist = dist;
					bestreg = ri;
				}
			}
		}
	}
	assert(bestreg); /* Must be able to spill something. Reconfigure the register allocator
		to ensure that we can allocate a register for all nodes without spilling
		the node's necessary input regs. */	
	assert(bestreg->x.regnode->vbl == NULL); /* Can't spill register variables because
		the reload site might be in other blocks. Reconfigure the register allocator
		to ensure that this register is never allocated to a variable. */
	return bestreg;
}
static int uses(Node p, Regnode rn) {
	int i;

	for (i = 0; i < NELEMS(p->x.kids); i++)
		if (
			p->x.kids[i] &&
			p->x.kids[i]->x.registered &&
			rn->set == p->x.kids[i]->syms[RX]->x.regnode->set &&
			(rn->mask&p->x.kids[i]->syms[RX]->x.regnode->mask)
		)
			return 1;
	return 0;
}
static void spillr(Symbol r, Node here) {
	int i;
	Symbol tmp;
	Node p = r->x.lastuse;
	assert(p);
	while (p->x.prevuse)
		assert(r == p->syms[RX]),
		p = p->x.prevuse;
	assert(p->x.registered && !readsreg(p));
	tmp = newtemp(AUTO, optype(p->op), opsize(p->op));
	genspill(r, p, tmp);
	for (p = here->x.next; p; p = p->x.next)
		for (i = 0; i < NELEMS(p->x.kids) && p->x.kids[i]; i++) {
			Node k = p->x.kids[i];
			if (k->x.registered && k->syms[RX] == r)
				genreload(p, tmp, i);
		}
	putreg(r);
}
static void genspill(Symbol r, Node last, Symbol tmp) {
	Node p, q;
	Symbol s;
	unsigned ty;

	debug(fprint(stderr, "(spilling %s to local %s)\n", r->x.name, tmp->x.name));
	debug(fprint(stderr, "(genspill: "));
	debug(dumptree(last));
	debug(fprint(stderr, ")\n"));
	ty = opkind(last->op);
	NEW0(s, FUNC);
	s->sclass = REGISTER;
	s->name = s->x.name = r->x.name;
	s->x.regnode = r->x.regnode;
	q = newnode(ADDRL+P + sizeop(IR->ptrmetric.size), NULL, NULL, s);
	q = newnode(INDIR + ty, q, NULL, NULL);
	p = newnode(ADDRL+P + sizeop(IR->ptrmetric.size), NULL, NULL, tmp);
	p = newnode(ASGN + ty, p, q, NULL);
	p->x.spills = 1;
	rewrite(p);
	prune(p, &q);
	q = last->x.next;
	linearize(p, q);
	for (p = last->x.next; p != q; p = p->x.next) {
		ralloc(p);
		assert(!p->x.listed || !NeedsReg[opindex(p->op)] || !(*IR->x.rmap)(opkind(p->op)));
	}
}

static void genreload(Node p, Symbol tmp, int i) {
	Node q;
	int ty;

	debug(fprint(stderr, "(replacing %x with a reload from %s)\n", p->x.kids[i], tmp->x.name));
	debug(fprint(stderr, "(genreload: "));
	debug(dumptree(p->x.kids[i]));
	debug(fprint(stderr, ")\n"));
	ty = opkind(p->x.kids[i]->op);
	q = newnode(ADDRL+P + sizeop(IR->ptrmetric.size), NULL, NULL, tmp);
	p->x.kids[i] = newnode(INDIR + ty, q, NULL, NULL);
	rewrite(p->x.kids[i]);
	prune(p->x.kids[i], &q);
	reprune(&p->kids[1], reprune(&p->kids[0], 0, i, p), i, p);
	prune(p, &q);
	linearize(p->x.kids[i], p);
}
static int reprune(Node *pp, int k, int n, Node p) {
	struct node x, *q = *pp;

	if (q == NULL || k > n)
		return k;
	else if (q->x.inst == 0)
		return reprune(&q->kids[1],
			reprune(&q->kids[0], k, n, p), n, p);
	if (k == n) {
		debug(fprint(stderr, "(reprune changes %x from %x to %x)\n", pp, *pp, p->x.kids[n]));
		*pp = p->x.kids[n];
		x = *p;
		(IR->x.target)(&x);
	}
	return k + 1;
}
void spill(unsigned mask, int n, Node here) {
	int i;
	Node p;

	here->x.spills = 1;
	usedmask[n] |= mask;
	if (mask&~freemask[n]) {

		assert( /* It makes no sense for a node to clobber() its target. */
			here->x.registered == 0 || /* call isn't coming through clobber() */
			here->syms[RX] == NULL ||
			here->syms[RX]->x.regnode == NULL ||
			here->syms[RX]->x.regnode->set != n ||
			(here->syms[RX]->x.regnode->mask&mask) == 0
		);

		for (p = here; p; p = p->x.next)
			for (i = 0; i < NELEMS(p->x.kids) && p->x.kids[i]; i++) {
				Symbol r = p->x.kids[i]->syms[RX];
				assert(r);
				if (p->x.kids[i]->x.registered && r->x.regnode->set == n
				&& r->x.regnode->mask&mask)
					spillr(r, here);
			}
	}
}
static void dumpregs(char *msg, char *a, char *b) {
	fprint(stderr, msg, a, b);
	fprint(stderr, "(free[0]=%x)\n", freemask[0]);
	fprint(stderr, "(free[1]=%x)\n", freemask[1]);
}

int getregnum(Node p) {
	assert(p && p->syms[RX] && p->syms[RX]->x.regnode);
	return p->syms[RX]->x.regnode->number;
}


unsigned regloc(Symbol p) {
	assert(p && p->sclass == REGISTER && p->x.regnode);
	return p->x.regnode->set<<8 | p->x.regnode->number;
}