Python/compile.c

/***********************************************************
Copyright 1991 by Stichting Mathematisch Centrum, Amsterdam, The
Netherlands.

                        All Rights Reserved

Permission to use, copy, modify, and distribute this software and its 
documentation for any purpose and without fee is hereby granted, 
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in 
supporting documentation, and that the names of Stichting Mathematisch
Centrum or CWI not be used in advertising or publicity pertaining to
distribution of the software without specific, written prior permission.

STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE
FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

******************************************************************/

/* Compile an expression node to intermediate code */

/* XXX TO DO:
   XXX Compute maximum needed stack sizes while compiling
   XXX Generate simple jump for break/return outside 'try...finally'
   XXX Include function name in code (and module names?)
*/

#include "allobjects.h"

#include "node.h"
#include "token.h"
#include "graminit.h"
#include "compile.h"
#include "opcode.h"
#include "structmember.h"

#include <ctype.h>

extern int errno;

#define OFF(x) offsetof(codeobject, x)

static struct memberlist code_memberlist[] = {
	{"co_code",	T_OBJECT,	OFF(co_code)},
	{"co_consts",	T_OBJECT,	OFF(co_consts)},
	{"co_names",	T_OBJECT,	OFF(co_names)},
	{"co_filename",	T_OBJECT,	OFF(co_filename)},
	{NULL}	/* Sentinel */
};

static object *
code_getattr(co, name)
	codeobject *co;
	char *name;
{
	return getmember((char *)co, code_memberlist, name);
}

static void
code_dealloc(co)
	codeobject *co;
{
	XDECREF(co->co_code);
	XDECREF(co->co_consts);
	XDECREF(co->co_names);
	XDECREF(co->co_filename);
	DEL(co);
}

typeobject Codetype = {
	OB_HEAD_INIT(&Typetype)
	0,
	"code",
	sizeof(codeobject),
	0,
	code_dealloc,	/*tp_dealloc*/
	0,		/*tp_print*/
	code_getattr,	/*tp_getattr*/
	0,		/*tp_setattr*/
	0,		/*tp_compare*/
	0,		/*tp_repr*/
	0,		/*tp_as_number*/
	0,		/*tp_as_sequence*/
	0,		/*tp_as_mapping*/
};

static codeobject *newcodeobject PROTO((object *, object *, object *, char *));

static codeobject *
newcodeobject(code, consts, names, filename)
	object *code;
	object *consts;
	object *names;
	char *filename;
{
	codeobject *co;
	int i;
	/* Check argument types */
	if (code == NULL || !is_stringobject(code) ||
		consts == NULL || !is_listobject(consts) ||
		names == NULL || !is_listobject(names)) {
		err_badcall();
		return NULL;
	}
	/* Make sure the list of names contains only strings */
	for (i = getlistsize(names); --i >= 0; ) {
		object *v = getlistitem(names, i);
		if (v == NULL || !is_stringobject(v)) {
			err_badcall();
			return NULL;
		}
	}
	co = NEWOBJ(codeobject, &Codetype);
	if (co != NULL) {
		INCREF(code);
		co->co_code = (stringobject *)code;
		INCREF(consts);
		co->co_consts = consts;
		INCREF(names);
		co->co_names = names;
		if ((co->co_filename = newstringobject(filename)) == NULL) {
			DECREF(co);
			co = NULL;
		}
	}
	return co;
}


/* Data structure used internally */
struct compiling {
	object *c_code;		/* string */
	object *c_consts;	/* list of objects */
	object *c_names;	/* list of strings (names) */
	int c_nexti;		/* index into c_code */
	int c_errors;		/* counts errors occurred */
	int c_infunction;	/* set when compiling a function */
	int c_loops;		/* counts nested loops */
	char *c_filename;	/* filename of current node */
};

/* Prototypes */
static int com_init PROTO((struct compiling *, char *));
static void com_free PROTO((struct compiling *));
static void com_done PROTO((struct compiling *));
static void com_node PROTO((struct compiling *, struct _node *));
static void com_addbyte PROTO((struct compiling *, int));
static void com_addint PROTO((struct compiling *, int));
static void com_addoparg PROTO((struct compiling *, int, int));
static void com_addfwref PROTO((struct compiling *, int, int *));
static void com_backpatch PROTO((struct compiling *, int));
static int com_add PROTO((struct compiling *, object *, object *));
static int com_addconst PROTO((struct compiling *, object *));
static int com_addname PROTO((struct compiling *, object *));
static void com_addopname PROTO((struct compiling *, int, node *));

static int
com_init(c, filename)
	struct compiling *c;
	char *filename;
{
	if ((c->c_code = newsizedstringobject((char *)NULL, 1000)) == NULL)
		goto fail_3;
	if ((c->c_consts = newlistobject(0)) == NULL)
		goto fail_2;
	if ((c->c_names = newlistobject(0)) == NULL)
		goto fail_1;
	c->c_nexti = 0;
	c->c_errors = 0;
	c->c_infunction = 0;
	c->c_loops = 0;
	c->c_filename = filename;
	return 1;
	
  fail_1:
	DECREF(c->c_consts);
  fail_2:
	DECREF(c->c_code);
  fail_3:
 	return 0;
}

static void
com_free(c)
	struct compiling *c;
{
	XDECREF(c->c_code);
	XDECREF(c->c_consts);
	XDECREF(c->c_names);
}

static void
com_done(c)
	struct compiling *c;
{
	if (c->c_code != NULL)
		resizestring(&c->c_code, c->c_nexti);
}

static void
com_addbyte(c, byte)
	struct compiling *c;
	int byte;
{
	int len;
	if (byte < 0 || byte > 255) {
		fprintf(stderr, "XXX compiling bad byte: %d\n", byte);
		abort();
		err_setstr(SystemError, "com_addbyte: byte out of range");
		c->c_errors++;
	}
	if (c->c_code == NULL)
		return;
	len = getstringsize(c->c_code);
	if (c->c_nexti >= len) {
		if (resizestring(&c->c_code, len+1000) != 0) {
			c->c_errors++;
			return;
		}
	}
	getstringvalue(c->c_code)[c->c_nexti++] = byte;
}

static void
com_addint(c, x)
	struct compiling *c;
	int x;
{
	com_addbyte(c, x & 0xff);
	com_addbyte(c, x >> 8); /* XXX x should be positive */
}

static void
com_addoparg(c, op, arg)
	struct compiling *c;
	int op;
	int arg;
{
	com_addbyte(c, op);
	com_addint(c, arg);
}

static void
com_addfwref(c, op, p_anchor)
	struct compiling *c;
	int op;
	int *p_anchor;
{
	/* Compile a forward reference for backpatching */
	int here;
	int anchor;
	com_addbyte(c, op);
	here = c->c_nexti;
	anchor = *p_anchor;
	*p_anchor = here;
	com_addint(c, anchor == 0 ? 0 : here - anchor);
}

static void
com_backpatch(c, anchor)
	struct compiling *c;
	int anchor; /* Must be nonzero */
{
	unsigned char *code = (unsigned char *) getstringvalue(c->c_code);
	int target = c->c_nexti;
	int lastanchor = 0;
	int dist;
	int prev;
	for (;;) {
		/* Make the JUMP instruction at anchor point to target */
		prev = code[anchor] + (code[anchor+1] << 8);
		dist = target - (anchor+2);
		code[anchor] = dist & 0xff;
		code[anchor+1] = dist >> 8;
		if (!prev)
			break;
		lastanchor = anchor;
		anchor -= prev;
	}
}

/* Handle constants and names uniformly */

static int
com_add(c, list, v)
	struct compiling *c;
	object *list;
	object *v;
{
	int n = getlistsize(list);
	int i;
	for (i = n; --i >= 0; ) {
		object *w = getlistitem(list, i);
		if (cmpobject(v, w) == 0)
			return i;
	}
	if (addlistitem(list, v) != 0)
		c->c_errors++;
	return n;
}

static int
com_addconst(c, v)
	struct compiling *c;
	object *v;
{
	return com_add(c, c->c_consts, v);
}

static int
com_addname(c, v)
	struct compiling *c;
	object *v;
{
	return com_add(c, c->c_names, v);
}

static void
com_addopname(c, op, n)
	struct compiling *c;
	int op;
	node *n;
{
	object *v;
	int i;
	char *name;
	if (TYPE(n) == STAR)
		name = "*";
	else {
		REQ(n, NAME);
		name = STR(n);
	}
	if ((v = newstringobject(name)) == NULL) {
		c->c_errors++;
		i = 255;
	}
	else {
		i = com_addname(c, v);
		DECREF(v);
	}
	com_addoparg(c, op, i);
}

static object *
parsenumber(s)
	char *s;
{
	extern long strtol();
	extern double strtod();
	char *end = s;
	long x;
	double xx;
	errno = 0;
	x = strtol(s, &end, 0);
	if (*end == '\0') {
		if (errno != 0) {
			err_setstr(RuntimeError, "integer constant too large");
			return NULL;
		}
		return newintobject(x);
	}
	if (*end == 'l' || *end == 'L') {
		extern object *long_scan();
		return long_scan(s, 0);
	}
	errno = 0;
	xx = strtod(s, &end);
	if (*end == '\0') {
		if (errno != 0) {
			err_setstr(RuntimeError, "float constant too large");
			return NULL;
		}
		return newfloatobject(xx);
	}
	err_setstr(RuntimeError, "bad number syntax");
	return NULL;
}

static object *
parsestr(s)
	char *s;
{
	object *v;
	int len;
	char *buf;
	char *p;
	int c;
	if (*s != '\'') {
		err_badcall();
		return NULL;
	}
	s++;
	len = strlen(s);
	if (s[--len] != '\'') {
		err_badcall();
		return NULL;
	}
	if (strchr(s, '\\') == NULL)
		return newsizedstringobject(s, len);
	v = newsizedstringobject((char *)NULL, len);
	p = buf = getstringvalue(v);
	while (*s != '\0' && *s != '\'') {
		if (*s != '\\') {
			*p++ = *s++;
			continue;
		}
		s++;
		switch (*s++) {
		/* XXX This assumes ASCII! */
		case '\\': *p++ = '\\'; break;
		case '\'': *p++ = '\''; break;
		case 'b': *p++ = '\b'; break;
		case 'f': *p++ = '\014'; break; /* FF */
		case 't': *p++ = '\t'; break;
		case 'n': *p++ = '\n'; break;
		case 'r': *p++ = '\r'; break;
		case 'v': *p++ = '\013'; break; /* VT */
		case 'E': *p++ = '\033'; break; /* ESC, not C */
		case 'a': *p++ = '\007'; break; /* BEL, not classic C */
		case '0': case '1': case '2': case '3':
		case '4': case '5': case '6': case '7':
			c = s[-1] - '0';
			if ('0' <= *s && *s <= '7') {
				c = (c<<3) + *s++ - '0';
				if ('0' <= *s && *s <= '7')
					c = (c<<3) + *s++ - '0';
			}
			*p++ = c;
			break;
		case 'x':
			if (isxdigit(*s)) {
				sscanf(s, "%x", &c);
				*p++ = c;
				do {
					s++;
				} while (isxdigit(*s));
				break;
			}
		/* FALLTHROUGH */
		default: *p++ = '\\'; *p++ = s[-1]; break;
		}
	}
	resizestring(&v, (int)(p - buf));
	return v;
}

static void
com_list_constructor(c, n)
	struct compiling *c;
	node *n;
{
	int len;
	int i;
	object *v, *w;
	if (TYPE(n) != testlist)
		REQ(n, exprlist);
	/* exprlist: expr (',' expr)* [',']; likewise for testlist */
	len = (NCH(n) + 1) / 2;
	for (i = 0; i < NCH(n); i += 2)
		com_node(c, CHILD(n, i));
	com_addoparg(c, BUILD_LIST, len);
}

static void
com_atom(c, n)
	struct compiling *c;
	node *n;
{
	node *ch;
	object *v;
	int i;
	REQ(n, atom);
	ch = CHILD(n, 0);
	switch (TYPE(ch)) {
	case LPAR:
		if (TYPE(CHILD(n, 1)) == RPAR)
			com_addoparg(c, BUILD_TUPLE, 0);
		else
			com_node(c, CHILD(n, 1));
		break;
	case LSQB:
		if (TYPE(CHILD(n, 1)) == RSQB)
			com_addoparg(c, BUILD_LIST, 0);
		else
			com_list_constructor(c, CHILD(n, 1));
		break;
	case LBRACE:
		com_addoparg(c, BUILD_MAP, 0);
		break;
	case BACKQUOTE:
		com_node(c, CHILD(n, 1));
		com_addbyte(c, UNARY_CONVERT);
		break;
	case NUMBER:
		if ((v = parsenumber(STR(ch))) == NULL) {
			c->c_errors++;
			i = 255;
		}
		else {
			i = com_addconst(c, v);
			DECREF(v);
		}
		com_addoparg(c, LOAD_CONST, i);
		break;
	case STRING:
		if ((v = parsestr(STR(ch))) == NULL) {
			c->c_errors++;
			i = 255;
		}
		else {
			i = com_addconst(c, v);
			DECREF(v);
		}
		com_addoparg(c, LOAD_CONST, i);
		break;
	case NAME:
		com_addopname(c, LOAD_NAME, ch);
		break;
	default:
		fprintf(stderr, "node type %d\n", TYPE(ch));
		err_setstr(SystemError, "com_atom: unexpected node type");
		c->c_errors++;
	}
}

static void
com_slice(c, n, op)
	struct compiling *c;
	node *n;
	int op;
{
	if (NCH(n) == 1) {
		com_addbyte(c, op);
	}
	else if (NCH(n) == 2) {
		if (TYPE(CHILD(n, 0)) != COLON) {
			com_node(c, CHILD(n, 0));
			com_addbyte(c, op+1);
		}
		else {
			com_node(c, CHILD(n, 1));
			com_addbyte(c, op+2);
		}
	}
	else {
		com_node(c, CHILD(n, 0));
		com_node(c, CHILD(n, 2));
		com_addbyte(c, op+3);
	}
}

static void
com_apply_subscript(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, subscript);
	if (NCH(n) == 1 && TYPE(CHILD(n, 0)) != COLON) {
		/* It's a single subscript */
		com_node(c, CHILD(n, 0));
		com_addbyte(c, BINARY_SUBSCR);
	}
	else {
		/* It's a slice: [expr] ':' [expr] */
		com_slice(c, n, SLICE);
	}
}

static void
com_call_function(c, n)
	struct compiling *c;
	node *n; /* EITHER testlist OR ')' */
{
	if (TYPE(n) == RPAR) {
		com_addbyte(c, UNARY_CALL);
	}
	else {
		com_node(c, n);
		com_addbyte(c, BINARY_CALL);
	}
}

static void
com_select_member(c, n)
	struct compiling *c;
	node *n;
{
	com_addopname(c, LOAD_ATTR, n);
}

static void
com_apply_trailer(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, trailer);
	switch (TYPE(CHILD(n, 0))) {
	case LPAR:
		com_call_function(c, CHILD(n, 1));
		break;
	case DOT:
		com_select_member(c, CHILD(n, 1));
		break;
	case LSQB:
		com_apply_subscript(c, CHILD(n, 1));
		break;
	default:
		err_setstr(SystemError,
			"com_apply_trailer: unknown trailer type");
		c->c_errors++;
	}
}

static void
com_factor(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	REQ(n, factor);
	if (TYPE(CHILD(n, 0)) == PLUS) {
		com_factor(c, CHILD(n, 1));
		com_addbyte(c, UNARY_POSITIVE);
	}
	else if (TYPE(CHILD(n, 0)) == MINUS) {
		com_factor(c, CHILD(n, 1));
		com_addbyte(c, UNARY_NEGATIVE);
	}
	else {
		com_atom(c, CHILD(n, 0));
		for (i = 1; i < NCH(n); i++)
			com_apply_trailer(c, CHILD(n, i));
	}
}

static void
com_term(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	int op;
	REQ(n, term);
	com_factor(c, CHILD(n, 0));
	for (i = 2; i < NCH(n); i += 2) {
		com_factor(c, CHILD(n, i));
		switch (TYPE(CHILD(n, i-1))) {
		case STAR:
			op = BINARY_MULTIPLY;
			break;
		case SLASH:
			op = BINARY_DIVIDE;
			break;
		case PERCENT:
			op = BINARY_MODULO;
			break;
		default:
			err_setstr(SystemError,
				"com_term: term operator not *, / or %");
			c->c_errors++;
			op = 255;
		}
		com_addbyte(c, op);
	}
}

static void
com_expr(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	int op;
	REQ(n, expr);
	com_term(c, CHILD(n, 0));
	for (i = 2; i < NCH(n); i += 2) {
		com_term(c, CHILD(n, i));
		switch (TYPE(CHILD(n, i-1))) {
		case PLUS:
			op = BINARY_ADD;
			break;
		case MINUS:
			op = BINARY_SUBTRACT;
			break;
		default:
			err_setstr(SystemError,
				"com_expr: expr operator not + or -");
			c->c_errors++;
			op = 255;
		}
		com_addbyte(c, op);
	}
}

static enum cmp_op
cmp_type(n)
	node *n;
{
	REQ(n, comp_op);
	/* comp_op: '<' | '>' | '=' | '>' '=' | '<' '=' | '<' '>'
	          | 'in' | 'not' 'in' | 'is' | 'is' not' */
	if (NCH(n) == 1) {
		n = CHILD(n, 0);
		switch (TYPE(n)) {
		case LESS:	return LT;
		case GREATER:	return GT;
		case EQUAL:	return EQ;
		case NAME:	if (strcmp(STR(n), "in") == 0) return IN;
				if (strcmp(STR(n), "is") == 0) return IS;
		}
	}
	else if (NCH(n) == 2) {
		int t2 = TYPE(CHILD(n, 1));
		switch (TYPE(CHILD(n, 0))) {
		case LESS:	if (t2 == EQUAL)	return LE;
				if (t2 == GREATER)	return NE;
				break;
		case GREATER:	if (t2 == EQUAL)	return GE;
				break;
		case NAME:	if (strcmp(STR(CHILD(n, 1)), "in") == 0)
					return NOT_IN;
				if (strcmp(STR(CHILD(n, 0)), "is") == 0)
					return IS_NOT;
		}
	}
	return BAD;
}

static void
com_comparison(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	enum cmp_op op;
	int anchor;
	REQ(n, comparison); /* comparison: expr (comp_op expr)* */
	com_expr(c, CHILD(n, 0));
	if (NCH(n) == 1)
		return;
	
	/****************************************************************
	   The following code is generated for all but the last
	   comparison in a chain:
	   
	   label:	on stack:	opcode:		jump to:
	   
			a		<code to load b>
			a, b		DUP_TOP
			a, b, b		ROT_THREE
			b, a, b		COMPARE_OP
			b, 0-or-1	JUMP_IF_FALSE	L1
			b, 1		POP_TOP
			b		
	
	   We are now ready to repeat this sequence for the next
	   comparison in the chain.
	   
	   For the last we generate:
	   
	   		b		<code to load c>
	   		b, c		COMPARE_OP
	   		0-or-1		
	   
	   If there were any jumps to L1 (i.e., there was more than one
	   comparison), we generate:
	   
	   		0-or-1		JUMP_FORWARD	L2
	   L1:		b, 0		ROT_TWO
	   		0, b		POP_TOP
	   		0
	   L2:
	****************************************************************/
	
	anchor = 0;
	
	for (i = 2; i < NCH(n); i += 2) {
		com_expr(c, CHILD(n, i));
		if (i+2 < NCH(n)) {
			com_addbyte(c, DUP_TOP);
			com_addbyte(c, ROT_THREE);
		}
		op = cmp_type(CHILD(n, i-1));
		if (op == BAD) {
			err_setstr(SystemError,
				"com_comparison: unknown comparison op");
			c->c_errors++;
		}
		com_addoparg(c, COMPARE_OP, op);
		if (i+2 < NCH(n)) {
			com_addfwref(c, JUMP_IF_FALSE, &anchor);
			com_addbyte(c, POP_TOP);
		}
	}
	
	if (anchor) {
		int anchor2 = 0;
		com_addfwref(c, JUMP_FORWARD, &anchor2);
		com_backpatch(c, anchor);
		com_addbyte(c, ROT_TWO);
		com_addbyte(c, POP_TOP);
		com_backpatch(c, anchor2);
	}
}

static void
com_not_test(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, not_test); /* 'not' not_test | comparison */
	if (NCH(n) == 1) {
		com_comparison(c, CHILD(n, 0));
	}
	else {
		com_not_test(c, CHILD(n, 1));
		com_addbyte(c, UNARY_NOT);
	}
}

static void
com_and_test(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	int anchor;
	REQ(n, and_test); /* not_test ('and' not_test)* */
	anchor = 0;
	i = 0;
	for (;;) {
		com_not_test(c, CHILD(n, i));
		if ((i += 2) >= NCH(n))
			break;
		com_addfwref(c, JUMP_IF_FALSE, &anchor);
		com_addbyte(c, POP_TOP);
	}
	if (anchor)
		com_backpatch(c, anchor);
}

static void
com_test(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	int anchor;
	REQ(n, test); /* and_test ('and' and_test)* */
	anchor = 0;
	i = 0;
	for (;;) {
		com_and_test(c, CHILD(n, i));
		if ((i += 2) >= NCH(n))
			break;
		com_addfwref(c, JUMP_IF_TRUE, &anchor);
		com_addbyte(c, POP_TOP);
	}
	if (anchor)
		com_backpatch(c, anchor);
}

static void
com_list(c, n)
	struct compiling *c;
	node *n;
{
	/* exprlist: expr (',' expr)* [',']; likewise for testlist */
	if (NCH(n) == 1) {
		com_node(c, CHILD(n, 0));
	}
	else {
		int i;
		int len;
		len = (NCH(n) + 1) / 2;
		for (i = 0; i < NCH(n); i += 2)
			com_node(c, CHILD(n, i));
		com_addoparg(c, BUILD_TUPLE, len);
	}
}


/* Begin of assignment compilation */

static void com_assign_name PROTO((struct compiling *, node *, int));
static void com_assign PROTO((struct compiling *, node *, int));

static void
com_assign_attr(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	com_addopname(c, assigning ? STORE_ATTR : DELETE_ATTR, n);
}

static void
com_assign_slice(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	com_slice(c, n, assigning ? STORE_SLICE : DELETE_SLICE);
}

static void
com_assign_subscript(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	com_node(c, n);
	com_addbyte(c, assigning ? STORE_SUBSCR : DELETE_SUBSCR);
}

static void
com_assign_trailer(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	char *name;
	REQ(n, trailer);
	switch (TYPE(CHILD(n, 0))) {
	case LPAR: /* '(' [exprlist] ')' */
		err_setstr(TypeError, "can't assign to function call");
		c->c_errors++;
		break;
	case DOT: /* '.' NAME */
		com_assign_attr(c, CHILD(n, 1), assigning);
		break;
	case LSQB: /* '[' subscript ']' */
		n = CHILD(n, 1);
		REQ(n, subscript); /* subscript: expr | [expr] ':' [expr] */
		if (NCH(n) > 1 || TYPE(CHILD(n, 0)) == COLON)
			com_assign_slice(c, n, assigning);
		else
			com_assign_subscript(c, CHILD(n, 0), assigning);
		break;
	default:
		err_setstr(TypeError, "unknown trailer type");
		c->c_errors++;
	}
}

static void
com_assign_tuple(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	int i;
	if (TYPE(n) != testlist)
		REQ(n, exprlist);
	if (assigning)
		com_addoparg(c, UNPACK_TUPLE, (NCH(n)+1)/2);
	for (i = 0; i < NCH(n); i += 2)
		com_assign(c, CHILD(n, i), assigning);
}

static void
com_assign_list(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	int i;
	if (assigning)
		com_addoparg(c, UNPACK_LIST, (NCH(n)+1)/2);
	for (i = 0; i < NCH(n); i += 2)
		com_assign(c, CHILD(n, i), assigning);
}

static void
com_assign_name(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	REQ(n, NAME);
	com_addopname(c, assigning ? STORE_NAME : DELETE_NAME, n);
}

static void
com_assign(c, n, assigning)
	struct compiling *c;
	node *n;
	int assigning;
{
	/* Loop to avoid trivial recursion */
	for (;;) {
		switch (TYPE(n)) {
		
		case exprlist:
		case testlist:
			if (NCH(n) > 1) {
				com_assign_tuple(c, n, assigning);
				return;
			}
			n = CHILD(n, 0);
			break;
		
		case test:
		case and_test:
		case not_test:
			if (NCH(n) > 1) {
				err_setstr(TypeError,
					"can't assign to operator");
				c->c_errors++;
				return;
			}
			n = CHILD(n, 0);
			break;
		
		case comparison:
			if (NCH(n) > 1) {
				err_setstr(TypeError,
					"can't assign to operator");
				c->c_errors++;
				return;
			}
			n = CHILD(n, 0);
			break;
		
		case expr:
			if (NCH(n) > 1) {
				err_setstr(TypeError,
					"can't assign to operator");
				c->c_errors++;
				return;
			}
			n = CHILD(n, 0);
			break;
		
		case term:
			if (NCH(n) > 1) {
				err_setstr(TypeError,
					"can't assign to operator");
				c->c_errors++;
				return;
			}
			n = CHILD(n, 0);
			break;
		
		case factor: /* ('+'|'-') factor | atom trailer* */
			if (TYPE(CHILD(n, 0)) != atom) { /* '+' | '-' */
				err_setstr(TypeError,
					"can't assign to operator");
				c->c_errors++;
				return;
			}
			if (NCH(n) > 1) { /* trailer present */
				int i;
				com_node(c, CHILD(n, 0));
				for (i = 1; i+1 < NCH(n); i++) {
					com_apply_trailer(c, CHILD(n, i));
				} /* NB i is still alive */
				com_assign_trailer(c,
						CHILD(n, i), assigning);
				return;
			}
			n = CHILD(n, 0);
			break;
		
		case atom:
			switch (TYPE(CHILD(n, 0))) {
			case LPAR:
				n = CHILD(n, 1);
				if (TYPE(n) == RPAR) {
					/* XXX Should allow () = () ??? */
					err_setstr(TypeError,
						"can't assign to ()");
					c->c_errors++;
					return;
				}
				break;
			case LSQB:
				n = CHILD(n, 1);
				if (TYPE(n) == RSQB) {
					err_setstr(TypeError,
						"can't assign to []");
					c->c_errors++;
					return;
				}
				com_assign_list(c, n, assigning);
				return;
			case NAME:
				com_assign_name(c, CHILD(n, 0), assigning);
				return;
			default:
				err_setstr(TypeError,
						"can't assign to constant");
				c->c_errors++;
				return;
			}
			break;
		
		default:
			fprintf(stderr, "node type %d\n", TYPE(n));
			err_setstr(SystemError, "com_assign: bad node");
			c->c_errors++;
			return;
		
		}
	}
}

static void
com_expr_stmt(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, expr_stmt); /* exprlist ('=' exprlist)* NEWLINE */
	com_node(c, CHILD(n, NCH(n)-2));
	if (NCH(n) == 2) {
		com_addbyte(c, PRINT_EXPR);
	}
	else {
		int i;
		for (i = 0; i < NCH(n)-3; i+=2) {
			if (i+2 < NCH(n)-3)
				com_addbyte(c, DUP_TOP);
			com_assign(c, CHILD(n, i), 1/*assign*/);
		}
	}
}

static void
com_print_stmt(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	REQ(n, print_stmt); /* 'print' (test ',')* [test] NEWLINE */
	for (i = 1; i+1 < NCH(n); i += 2) {
		com_node(c, CHILD(n, i));
		com_addbyte(c, PRINT_ITEM);
	}
	if (TYPE(CHILD(n, NCH(n)-2)) != COMMA)
		com_addbyte(c, PRINT_NEWLINE);
		/* XXX Alternatively, LOAD_CONST '\n' and then PRINT_ITEM */
}

static void
com_return_stmt(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, return_stmt); /* 'return' [testlist] NEWLINE */
	if (!c->c_infunction) {
		err_setstr(TypeError, "'return' outside function");
		c->c_errors++;
	}
	if (NCH(n) == 2)
		com_addoparg(c, LOAD_CONST, com_addconst(c, None));
	else
		com_node(c, CHILD(n, 1));
	com_addbyte(c, RETURN_VALUE);
}

static void
com_raise_stmt(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, raise_stmt); /* 'raise' expr [',' expr] NEWLINE */
	com_node(c, CHILD(n, 1));
	if (NCH(n) > 3)
		com_node(c, CHILD(n, 3));
	else
		com_addoparg(c, LOAD_CONST, com_addconst(c, None));
	com_addbyte(c, RAISE_EXCEPTION);
}

static void
com_import_stmt(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	REQ(n, import_stmt);
	/* 'import' NAME (',' NAME)* NEWLINE |
	   'from' NAME 'import' ('*' | NAME (',' NAME)*) NEWLINE */
	if (STR(CHILD(n, 0))[0] == 'f') {
		/* 'from' NAME 'import' ... */
		REQ(CHILD(n, 1), NAME);
		com_addopname(c, IMPORT_NAME, CHILD(n, 1));
		for (i = 3; i < NCH(n); i += 2)
			com_addopname(c, IMPORT_FROM, CHILD(n, i));
		com_addbyte(c, POP_TOP);
	}
	else {
		/* 'import' ... */
		for (i = 1; i < NCH(n); i += 2) {
			com_addopname(c, IMPORT_NAME, CHILD(n, i));
			com_addopname(c, STORE_NAME, CHILD(n, i));
		}
	}
}

static void
com_if_stmt(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	int anchor = 0;
	REQ(n, if_stmt);
	/*'if' test ':' suite ('elif' test ':' suite)* ['else' ':' suite] */
	for (i = 0; i+3 < NCH(n); i+=4) {
		int a = 0;
		node *ch = CHILD(n, i+1);
		if (i > 0)
			com_addoparg(c, SET_LINENO, ch->n_lineno);
		com_node(c, CHILD(n, i+1));
		com_addfwref(c, JUMP_IF_FALSE, &a);
		com_addbyte(c, POP_TOP);
		com_node(c, CHILD(n, i+3));
		com_addfwref(c, JUMP_FORWARD, &anchor);
		com_backpatch(c, a);
		com_addbyte(c, POP_TOP);
	}
	if (i+2 < NCH(n))
		com_node(c, CHILD(n, i+2));
	com_backpatch(c, anchor);
}

static void
com_while_stmt(c, n)
	struct compiling *c;
	node *n;
{
	int break_anchor = 0;
	int anchor = 0;
	int begin;
	REQ(n, while_stmt); /* 'while' test ':' suite ['else' ':' suite] */
	com_addfwref(c, SETUP_LOOP, &break_anchor);
	begin = c->c_nexti;
	com_addoparg(c, SET_LINENO, n->n_lineno);
	com_node(c, CHILD(n, 1));
	com_addfwref(c, JUMP_IF_FALSE, &anchor);
	com_addbyte(c, POP_TOP);
	c->c_loops++;
	com_node(c, CHILD(n, 3));
	c->c_loops--;
	com_addoparg(c, JUMP_ABSOLUTE, begin);
	com_backpatch(c, anchor);
	com_addbyte(c, POP_TOP);
	com_addbyte(c, POP_BLOCK);
	if (NCH(n) > 4)
		com_node(c, CHILD(n, 6));
	com_backpatch(c, break_anchor);
}

static void
com_for_stmt(c, n)
	struct compiling *c;
	node *n;
{
	object *v;
	int break_anchor = 0;
	int anchor = 0;
	int begin;
	REQ(n, for_stmt);
	/* 'for' exprlist 'in' exprlist ':' suite ['else' ':' suite] */
	com_addfwref(c, SETUP_LOOP, &break_anchor);
	com_node(c, CHILD(n, 3));
	v = newintobject(0L);
	if (v == NULL)
		c->c_errors++;
	com_addoparg(c, LOAD_CONST, com_addconst(c, v));
	XDECREF(v);
	begin = c->c_nexti;
	com_addoparg(c, SET_LINENO, n->n_lineno);
	com_addfwref(c, FOR_LOOP, &anchor);
	com_assign(c, CHILD(n, 1), 1/*assigning*/);
	c->c_loops++;
	com_node(c, CHILD(n, 5));
	c->c_loops--;
	com_addoparg(c, JUMP_ABSOLUTE, begin);
	com_backpatch(c, anchor);
	com_addbyte(c, POP_BLOCK);
	if (NCH(n) > 8)
		com_node(c, CHILD(n, 8));
	com_backpatch(c, break_anchor);
}

/* Although 'execpt' and 'finally' clauses can be combined
   syntactically, they are compiled separately.  In fact,
	try: S
	except E1: S1
	except E2: S2
	...
	finally: Sf
   is equivalent to
	try:
	    try: S
	    except E1: S1
	    except E2: S2
	    ...
	finally: Sf
   meaning that the 'finally' clause is entered even if things
   go wrong again in an exception handler.  Note that this is
   not the case for exception handlers: at most one is entered.
   
   Code generated for "try: S finally: Sf" is as follows:
   
		SETUP_FINALLY	L
		<code for S>
		POP_BLOCK
		LOAD_CONST	<nil>
	L:	<code for Sf>
		END_FINALLY
   
   The special instructions use the block stack.  Each block
   stack entry contains the instruction that created it (here
   SETUP_FINALLY), the level of the value stack at the time the
   block stack entry was created, and a label (here L).
   
   SETUP_FINALLY:
	Pushes the current value stack level and the label
	onto the block stack.
   POP_BLOCK:
	Pops en entry from the block stack, and pops the value
	stack until its level is the same as indicated on the
	block stack.  (The label is ignored.)
   END_FINALLY:
	Pops a variable number of entries from the *value* stack
	and re-raises the exception they specify.  The number of
	entries popped depends on the (pseudo) exception type.
   
   The block stack is unwound when an exception is raised:
   when a SETUP_FINALLY entry is found, the exception is pushed
   onto the value stack (and the exception condition is cleared),
   and the interpreter jumps to the label gotten from the block
   stack.
   
   Code generated for "try: S except E1, V1: S1 except E2, V2: S2 ...":
   (The contents of the value stack is shown in [], with the top
   at the right; 'tb' is trace-back info, 'val' the exception's
   associated value, and 'exc' the exception.)
   
   Value stack		Label	Instruction	Argument
   []				SETUP_EXCEPT	L1
   []				<code for S>
   []				POP_BLOCK
   []				JUMP_FORWARD	L0
   
   [tb, val, exc]	L1:	DUP				)
   [tb, val, exc, exc]		<evaluate E1>			)
   [tb, val, exc, exc, E1]	COMPARE_OP	EXC_MATCH	) only if E1
   [tb, val, exc, 1-or-0]	JUMP_IF_FALSE	L2		)
   [tb, val, exc, 1]		POP				)
   [tb, val, exc]		POP
   [tb, val]			<assign to V1>	(or POP if no V1)
   [tb]				POP
   []				<code for S1>
   				JUMP_FORWARD	L0
   
   [tb, val, exc, 0]	L2:	POP
   [tb, val, exc]		DUP
   .............................etc.......................

   [tb, val, exc, 0]	Ln+1:	POP
   [tb, val, exc]	   	END_FINALLY	# re-raise exception
   
   []			L0:	<next statement>
   
   Of course, parts are not generated if Vi or Ei is not present.
*/

static void
com_try_stmt(c, n)
	struct compiling *c;
	node *n;
{
	int finally_anchor = 0;
	int except_anchor = 0;
	REQ(n, try_stmt);
	/* 'try' ':' suite (except_clause ':' suite)* ['finally' ':' suite] */
	
	if (NCH(n) > 3 && TYPE(CHILD(n, NCH(n)-3)) != except_clause) {
		/* Have a 'finally' clause */
		com_addfwref(c, SETUP_FINALLY, &finally_anchor);
	}
	if (NCH(n) > 3 && TYPE(CHILD(n, 3)) == except_clause) {
		/* Have an 'except' clause */
		com_addfwref(c, SETUP_EXCEPT, &except_anchor);
	}
	com_node(c, CHILD(n, 2));
	if (except_anchor) {
		int end_anchor = 0;
		int i;
		node *ch;
		com_addbyte(c, POP_BLOCK);
		com_addfwref(c, JUMP_FORWARD, &end_anchor);
		com_backpatch(c, except_anchor);
		for (i = 3;
			i < NCH(n) && TYPE(ch = CHILD(n, i)) == except_clause;
								i += 3) {
			/* except_clause: 'except' [expr [',' expr]] */
			if (except_anchor == 0) {
				err_setstr(TypeError,
					"default 'except:' must be last");
				c->c_errors++;
				break;
			}
			except_anchor = 0;
			com_addoparg(c, SET_LINENO, ch->n_lineno);
			if (NCH(ch) > 1) {
				com_addbyte(c, DUP_TOP);
				com_node(c, CHILD(ch, 1));
				com_addoparg(c, COMPARE_OP, EXC_MATCH);
				com_addfwref(c, JUMP_IF_FALSE, &except_anchor);
				com_addbyte(c, POP_TOP);
			}
			com_addbyte(c, POP_TOP);
			if (NCH(ch) > 3)
				com_assign(c, CHILD(ch, 3), 1/*assigning*/);
			else
				com_addbyte(c, POP_TOP);
			com_addbyte(c, POP_TOP);
			com_node(c, CHILD(n, i+2));
			com_addfwref(c, JUMP_FORWARD, &end_anchor);
			if (except_anchor) {
				com_backpatch(c, except_anchor);
				com_addbyte(c, POP_TOP);
			}
		}
		com_addbyte(c, END_FINALLY);
		com_backpatch(c, end_anchor);
	}
	if (finally_anchor) {
		node *ch;
		com_addbyte(c, POP_BLOCK);
		com_addoparg(c, LOAD_CONST, com_addconst(c, None));
		com_backpatch(c, finally_anchor);
		ch = CHILD(n, NCH(n)-1);
		com_addoparg(c, SET_LINENO, ch->n_lineno);
		com_node(c, ch);
		com_addbyte(c, END_FINALLY);
	}
}

static void
com_suite(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, suite);
	/* simple_stmt | NEWLINE INDENT NEWLINE* (stmt NEWLINE*)+ DEDENT */
	if (NCH(n) == 1) {
		com_node(c, CHILD(n, 0));
	}
	else {
		int i;
		for (i = 0; i < NCH(n); i++) {
			node *ch = CHILD(n, i);
			if (TYPE(ch) == stmt)
				com_node(c, ch);
		}
	}
}

static void
com_funcdef(c, n)
	struct compiling *c;
	node *n;
{
	object *v;
	REQ(n, funcdef); /* funcdef: 'def' NAME parameters ':' suite */
	v = (object *)compile(n, c->c_filename);
	if (v == NULL)
		c->c_errors++;
	else {
		int i = com_addconst(c, v);
		com_addoparg(c, LOAD_CONST, i);
		com_addbyte(c, BUILD_FUNCTION);
		com_addopname(c, STORE_NAME, CHILD(n, 1));
		DECREF(v);
	}
}

static void
com_bases(c, n)
	struct compiling *c;
	node *n;
{
	int i, nbases;
	REQ(n, baselist);
	/*
	baselist: atom arguments (',' atom arguments)*
	arguments: '(' [testlist] ')'
	*/
	for (i = 0; i < NCH(n); i += 3)
		com_node(c, CHILD(n, i));
	com_addoparg(c, BUILD_TUPLE, (NCH(n)+1) / 3);
}

static void
com_classdef(c, n)
	struct compiling *c;
	node *n;
{
	object *v;
	REQ(n, classdef);
	/*
	classdef: 'class' NAME parameters ['=' baselist] ':' suite
	baselist: atom arguments (',' atom arguments)*
	arguments: '(' [testlist] ')'
	*/
	if (NCH(n) == 7)
		com_bases(c, CHILD(n, 4));
	else
		com_addoparg(c, LOAD_CONST, com_addconst(c, None));
	v = (object *)compile(n, c->c_filename);
	if (v == NULL)
		c->c_errors++;
	else {
		int i = com_addconst(c, v);
		com_addoparg(c, LOAD_CONST, i);
		com_addbyte(c, BUILD_FUNCTION);
		com_addbyte(c, UNARY_CALL);
		com_addbyte(c, BUILD_CLASS);
		com_addopname(c, STORE_NAME, CHILD(n, 1));
		DECREF(v);
	}
}

static void
com_node(c, n)
	struct compiling *c;
	node *n;
{
	switch (TYPE(n)) {
	
	/* Definition nodes */
	
	case funcdef:
		com_funcdef(c, n);
		break;
	case classdef:
		com_classdef(c, n);
		break;
	
	/* Trivial parse tree nodes */
	
	case stmt:
	case flow_stmt:
		com_node(c, CHILD(n, 0));
		break;

	case simple_stmt:
	case compound_stmt:
		com_addoparg(c, SET_LINENO, n->n_lineno);
		com_node(c, CHILD(n, 0));
		break;

	/* Statement nodes */
	
	case expr_stmt:
		com_expr_stmt(c, n);
		break;
	case print_stmt:
		com_print_stmt(c, n);
		break;
	case del_stmt: /* 'del' exprlist NEWLINE */
		com_assign(c, CHILD(n, 1), 0/*delete*/);
		break;
	case pass_stmt:
		break;
	case break_stmt:
		if (c->c_loops == 0) {
			err_setstr(TypeError, "'break' outside loop");
			c->c_errors++;
		}
		com_addbyte(c, BREAK_LOOP);
		break;
	case return_stmt:
		com_return_stmt(c, n);
		break;
	case raise_stmt:
		com_raise_stmt(c, n);
		break;
	case import_stmt:
		com_import_stmt(c, n);
		break;
	case if_stmt:
		com_if_stmt(c, n);
		break;
	case while_stmt:
		com_while_stmt(c, n);
		break;
	case for_stmt:
		com_for_stmt(c, n);
		break;
	case try_stmt:
		com_try_stmt(c, n);
		break;
	case suite:
		com_suite(c, n);
		break;
	
	/* Expression nodes */
	
	case testlist:
		com_list(c, n);
		break;
	case test:
		com_test(c, n);
		break;
	case and_test:
		com_and_test(c, n);
		break;
	case not_test:
		com_not_test(c, n);
		break;
	case comparison:
		com_comparison(c, n);
		break;
	case exprlist:
		com_list(c, n);
		break;
	case expr:
		com_expr(c, n);
		break;
	case term:
		com_term(c, n);
		break;
	case factor:
		com_factor(c, n);
		break;
	case atom:
		com_atom(c, n);
		break;
	
	default:
		fprintf(stderr, "node type %d\n", TYPE(n));
		err_setstr(SystemError, "com_node: unexpected node type");
		c->c_errors++;
	}
}

static void com_fplist PROTO((struct compiling *, node *));

static void
com_fpdef(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, fpdef); /* fpdef: NAME | '(' fplist ')' */
	if (TYPE(CHILD(n, 0)) == LPAR)
		com_fplist(c, CHILD(n, 1));
	else
		com_addopname(c, STORE_NAME, CHILD(n, 0));
}

static void
com_fplist(c, n)
	struct compiling *c;
	node *n;
{
	REQ(n, fplist); /* fplist: fpdef (',' fpdef)* */
	if (NCH(n) == 1) {
		com_fpdef(c, CHILD(n, 0));
	}
	else {
		int i;
		com_addoparg(c, UNPACK_TUPLE, (NCH(n)+1)/2);
		for (i = 0; i < NCH(n); i += 2)
			com_fpdef(c, CHILD(n, i));
	}
}

static void
com_file_input(c, n)
	struct compiling *c;
	node *n;
{
	int i;
	REQ(n, file_input); /* (NEWLINE | stmt)* ENDMARKER */
	for (i = 0; i < NCH(n); i++) {
		node *ch = CHILD(n, i);
		if (TYPE(ch) != ENDMARKER && TYPE(ch) != NEWLINE)
			com_node(c, ch);
	}
}

/* Top-level compile-node interface */

static void
compile_funcdef(c, n)
	struct compiling *c;
	node *n;
{
	node *ch;
	REQ(n, funcdef); /* funcdef: 'def' NAME parameters ':' suite */
	ch = CHILD(n, 2); /* parameters: '(' [fplist] ')' */
	ch = CHILD(ch, 1); /* ')' | fplist */
	if (TYPE(ch) == RPAR)
		com_addbyte(c, REFUSE_ARGS);
	else {
		com_addbyte(c, REQUIRE_ARGS);
		com_fplist(c, ch);
	}
	c->c_infunction = 1;
	com_node(c, CHILD(n, 4));
	c->c_infunction = 0;
	com_addoparg(c, LOAD_CONST, com_addconst(c, None));
	com_addbyte(c, RETURN_VALUE);
}

static void
compile_node(c, n)
	struct compiling *c;
	node *n;
{
	com_addoparg(c, SET_LINENO, n->n_lineno);
	
	switch (TYPE(n)) {
	
	case single_input: /* One interactive command */
		/* NEWLINE | simple_stmt | compound_stmt NEWLINE */
		com_addbyte(c, REFUSE_ARGS);
		n = CHILD(n, 0);
		if (TYPE(n) != NEWLINE)
			com_node(c, n);
		com_addoparg(c, LOAD_CONST, com_addconst(c, None));
		com_addbyte(c, RETURN_VALUE);
		break;
	
	case file_input: /* A whole file, or built-in function exec() */
		com_addbyte(c, REFUSE_ARGS);
		com_file_input(c, n);
		com_addoparg(c, LOAD_CONST, com_addconst(c, None));
		com_addbyte(c, RETURN_VALUE);
		break;
	
	case expr_input: /* Built-in function eval() */
		com_addbyte(c, REFUSE_ARGS);
		com_node(c, CHILD(n, 0));
		com_addbyte(c, RETURN_VALUE);
		break;
	
	case eval_input: /* Built-in function input() */
		com_addbyte(c, REFUSE_ARGS);
		com_node(c, CHILD(n, 0));
		com_addbyte(c, RETURN_VALUE);
		break;
	
	case funcdef: /* A function definition */
		compile_funcdef(c, n);
		break;
	
	case classdef: /* A class definition */
		/* 'class' NAME parameters ['=' baselist] ':' suite */
		com_addbyte(c, REFUSE_ARGS);
		com_node(c, CHILD(n, NCH(n)-1));
		com_addbyte(c, LOAD_LOCALS);
		com_addbyte(c, RETURN_VALUE);
		break;
	
	default:
		fprintf(stderr, "node type %d\n", TYPE(n));
		err_setstr(SystemError, "compile_node: unexpected node type");
		c->c_errors++;
	}
}

/* Optimization for local and global variables.

   Attempt to replace all LOAD_NAME instructions that refer to a local
   variable with LOAD_LOCAL instructions, and all that refer to a global
   variable with LOAD_GLOBAL instructions.
   
   To find all local variables, we check all STORE_NAME and IMPORT_FROM
   instructions.  This yields all local variables, including arguments,
   function definitions, class definitions and import statements.
   
   There is one leak: 'from foo import *' introduces local variables
   that we can't know while compiling.  If this is the case, LOAD_GLOBAL
   instructions are not generated -- LOAD_NAME is left in place for
   globals, since it first checks for globals (LOAD_LOCAL is still used
   for recognized locals, since it doesn't hurt).
   
   This optimization means that using the same name as a global and
   as a local variable within the same scope is now illegal, which
   is a change to the language!  Also using eval() to introduce new
   local variables won't work.  But both were bad practice at best.
   
   The optimization doesn't save much: basically, it saves one
   unsuccessful dictionary lookup per global (or built-in) variable
   reference.  On the (slow!) Mac Plus, with 4 local variables,
   this saving was measured to be about 0.18 ms.  We might save more
   by using a different data structure to hold local variables, like
   an array indexed by variable number.
   
   NB: this modifies the string object co->co_code!
*/

static void
optimizer(co)
	codeobject *co;
{
	unsigned char *next_instr, *cur_instr;
	object *locals;
	int opcode;
	int oparg;
	object *name;
	int star_used;

#define NEXTOP()	(*next_instr++)
#define NEXTARG()	(next_instr += 2, (next_instr[-1]<<8) + next_instr[-2])
#define GETITEM(v, i)	(getlistitem((v), (i)))
#define GETNAMEOBJ(i)	(GETITEM(co->co_names, (i)))

	locals = newdictobject();
	if (locals == NULL) {
		err_clear();
		return; /* For now, this is OK */
	}
	
	next_instr = (unsigned char *) GETSTRINGVALUE(co->co_code); 
	for (;;) {
		opcode = NEXTOP();
		if (opcode == STOP_CODE)
			break;
		if (HAS_ARG(opcode))
			oparg = NEXTARG();
		if (opcode == STORE_NAME || opcode == IMPORT_FROM) {
			name = GETNAMEOBJ(oparg);
			if (dict2insert(locals, name, None) != 0) {
				DECREF(locals);
				return; /* Sorry */
			}
		}
	}
	
	star_used = (dictlookup(locals, "*") != NULL);
	next_instr = (unsigned char *) GETSTRINGVALUE(co->co_code); 
	for (;;) {
		cur_instr = next_instr;
		opcode = NEXTOP();
		if (opcode == STOP_CODE)
			break;
		if (HAS_ARG(opcode))
			oparg = NEXTARG();
		if (opcode == LOAD_NAME) {
			name = GETNAMEOBJ(oparg);
			if (dictlookup(locals, getstringvalue(name)) != NULL)
				*cur_instr = LOAD_LOCAL;
			else if (!star_used)
				*cur_instr = LOAD_GLOBAL;
		}
	}
	
	DECREF(locals);
}

codeobject *
compile(n, filename)
	node *n;
	char *filename;
{
	struct compiling sc;
	codeobject *co;
	if (!com_init(&sc, filename))
		return NULL;
	compile_node(&sc, n);
	com_done(&sc);
	if (sc.c_errors == 0)
		co = newcodeobject(sc.c_code, sc.c_consts, sc.c_names, filename);
	else
		co = NULL;
	com_free(&sc);
	if (co != NULL && filename[0] != '<')
		optimizer(co);
	return co;
}