Instead of emitting SET_LINENO instructions, generate a line number

table which is incorporated in the code object.  This way, the runtime
overhead to keep track of line numbers is only incurred when an
exception has to be reported.

Python/compile.c

@@ -76,6 +76,8 @@ static struct memberlist code_memberlist[] = {
 	{"co_varnames",	T_OBJECT,	OFF(co_varnames),	READONLY},
 	{"co_filename",	T_OBJECT,	OFF(co_filename),	READONLY},
 	{"co_name",	T_OBJECT,	OFF(co_name),		READONLY},
+	{"co_firstlineno", T_INT,	OFF(co_firstlineno),	READONLY},
+	{"co_lnotab",	T_OBJECT,	OFF(co_lnotab),		READONLY},
 	{NULL}	/* Sentinel */
 };
 
@@ -180,7 +182,8 @@ typeobject Codetype = {
 
 codeobject *
 newcodeobject(argcount, nlocals, stacksize, flags,
-	      code, consts, names, varnames, filename, name)
+	      code, consts, names, varnames, filename, name,
+	      firstlineno, lnotab)
 	int argcount;
 	int nlocals;
 	int stacksize;
@@ -191,6 +194,8 @@ newcodeobject(argcount, nlocals, stacksize, flags,
 	object *varnames;
 	object *filename;
 	object *name;
+	int firstlineno;
+	object *lnotab;
 {
 	codeobject *co;
 	int i;
@@ -201,7 +206,8 @@ newcodeobject(argcount, nlocals, stacksize, flags,
 	    names == NULL || !is_tupleobject(names) ||
 	    varnames == NULL || !is_tupleobject(varnames) ||
 	    name == NULL || !is_stringobject(name) ||
-	    filename == NULL || !is_stringobject(filename)) {
+	    filename == NULL || !is_stringobject(filename) ||
+		lnotab == NULL || !is_stringobject(lnotab)) {
 		err_badcall();
 		return NULL;
 	}
@@ -252,6 +258,9 @@ newcodeobject(argcount, nlocals, stacksize, flags,
 		co->co_filename = filename;
 		INCREF(name);
 		co->co_name = name;
+		co->co_firstlineno = firstlineno;
+		INCREF(lnotab);
+		co->co_lnotab = lnotab;
 	}
 	return co;
 }
@@ -282,6 +291,9 @@ struct compiling {
 	int c_lineno;		/* Current line number */
 	int c_stacklevel;	/* Current stack level */
 	int c_maxstacklevel;	/* Maximum stack level */
+	int c_firstlineno;
+	object *c_lnotab;	/* Table mapping address to line number */
+	int c_last_addr, c_last_line, c_lnotab_next;
 #ifdef PRIVATE_NAME_MANGLING
 	char *c_private;	/* for private name mangling */
 #endif
@@ -387,6 +399,8 @@ com_init(c, filename)
 		goto fail_00;
 	if ((c->c_varnames = newlistobject(0)) == NULL)
 		goto fail_000;
+	if ((c->c_lnotab = newsizedstringobject((char *)NULL, 1000)) == NULL)
+		goto fail_0000;
 	c->c_nlocals = 0;
 	c->c_argcount = 0;
 	c->c_flags = 0;
@@ -402,8 +416,14 @@ com_init(c, filename)
 	c->c_lineno = 0;
 	c->c_stacklevel = 0;
 	c->c_maxstacklevel = 0;
+	c->c_firstlineno = 0;
+	c->c_last_addr = 0;
+	c->c_last_line = 0;
+	c-> c_lnotab_next = 0;
 	return 1;
 	
+  fail_0000:
+  	DECREF(c->c_lnotab);
   fail_000:
   	DECREF(c->c_locals);
   fail_00:
@@ -428,6 +448,7 @@ com_free(c)
 	XDECREF(c->c_globals);
 	XDECREF(c->c_locals);
 	XDECREF(c->c_varnames);
+	XDECREF(c->c_lnotab);
 }
 
 static void
@@ -462,6 +483,8 @@ com_done(c)
 {
 	if (c->c_code != NULL)
 		resizestring(&c->c_code, c->c_nexti);
+	if (c->c_lnotab != NULL)
+		resizestring(&c->c_lnotab, c->c_lnotab_next);
 }
 
 static void
@@ -499,6 +522,57 @@ com_addint(c, x)
 	com_addbyte(c, x >> 8); /* XXX x should be positive */
 }
 
+static void
+com_add_lnotab(c, addr, line)
+	struct compiling *c;
+	int addr;
+	int line;
+{
+	int size;
+	char *p;
+	if (c->c_lnotab == NULL)
+		return;
+	size = getstringsize(c->c_lnotab);
+	if (c->c_lnotab_next+2 > size) {
+		if (resizestring(&c->c_lnotab, size + 1000) < 0) {
+			c->c_errors++;
+			return;
+		}
+	}
+	p = getstringvalue(c->c_lnotab) + c->c_lnotab_next;
+	*p++ = addr;
+	*p++ = line;
+	c->c_lnotab_next += 2;
+}
+
+static void
+com_set_lineno(c, lineno)
+	struct compiling *c;
+	int lineno;
+{
+	c->c_lineno = lineno;
+	if (c->c_firstlineno == 0) {
+		c->c_firstlineno = c->c_last_line = lineno;
+	}
+	else {
+		int incr_addr = c->c_nexti - c->c_last_addr;
+		int incr_line = lineno - c->c_last_line;
+		while (incr_addr > 0 || incr_line > 0) {
+			int trunc_addr = incr_addr;
+			int trunc_line = incr_line;
+			if (trunc_addr > 255)
+				trunc_addr = 255;
+			if (trunc_line > 255)
+				trunc_line = 255;
+			com_add_lnotab(c, trunc_addr, trunc_line);
+			incr_addr -= trunc_addr;
+			incr_line -= trunc_line;
+		}
+		c->c_last_addr = c->c_nexti;
+		c->c_last_line = lineno;
+	}
+}
+
 static void
 com_addoparg(c, op, arg)
 	struct compiling *c;
@@ -506,9 +580,11 @@ com_addoparg(c, op, arg)
 	int arg;
 {
 	if (op == SET_LINENO)
-		c->c_lineno = arg;
+		com_set_lineno(c, arg);
+	else {
 		com_addbyte(c, op);
 		com_addint(c, arg);
+	}
 }
 
 static void
@@ -3212,7 +3288,9 @@ jcompile(n, filename, base)
 					   names,
 					   varnames,
 					   filename,
-					   name);
+					   name,
+					   sc.c_firstlineno,
+					   sc.c_lnotab);
 		XDECREF(consts);
 		XDECREF(names);
 		XDECREF(varnames);
@@ -3222,3 +3300,21 @@ jcompile(n, filename, base)
 	com_free(&sc);
 	return co;
 }
+
+int
+PyCode_Addr2Line(co, addrq)
+	PyCodeObject *co;
+	int addrq;
+{
+	int size = PyString_Size(co->co_lnotab) / 2;
+	char *p = PyString_AsString(co->co_lnotab);
+	int line = co->co_firstlineno;
+	int addr = 0;
+	while (--size >= 0) {
+		addr += *p++;
+		if (addr > addrq)
+			break;
+		line += *p++;
+	}
+	return line;
+}