Remove the useless rules from the parser.

Remove the useless rules from the parser.
* src/gram.h, src/gram.c (rules_swap, rule_rhs_length): New.
(ritem_longest_rhs): Use the latter.
* src/gram.h (rule_t): `number' is a new member.
* src/reader.c (packgram): Set it.
* src/reduce.c (reduce_grammar_tables): Move the useless rules at
the end of `rules', and count them out of `nrules'.
(reduce_output, dump_grammar): Adjust.
* src/print.c (print_grammar): It is no longer needed to check for
the usefulness of a rule, as useless rules are beyond `nrules + 1'.
* tests/reduce.at (Reduced Automaton): New test.
Changes in version 1.49a:
* False `Token not used' report fixed.
On a grammar such as
/* Allocate input grammar variables for bison,
This file is part of Bison, the GNU Compiler Compiler.
int error_token_number;
/*------------------------.
| Dump RITEM for traces.  |
`------------------------*/
size_t
ritem_longest_rhs (void)
{
int i;
return max;
}
typedef struct rule_s
{
short lhs;
short *rhs;
short prec;
extern int error_token_number;
/* Dump RITEM for traces. */
void ritem_print PARAMS ((FILE *out));
fprintf (out, "%snn", _("Grammar"));
fprintf (out, "  %sn", _("Number, Line, Rule"));
for (i = 1; i < nrules + 1; i++)
fputs ("nn", out);
while (p)
{
bucket *ruleprec = p->ruleprec;
rules[ruleno].lhs = p->sym->number;
rules[ruleno].rhs = ritem + itemno;
rules[ruleno].line = p->line;
bitset_set (V1, rules[i].precsym);
}
static void
reduce_grammar_tables (void)
{
if (nuseless_productions > 0)
{
int pn;
for (pn = 1; pn < nrules + 1; pn++)
rules[pn].useful = bitset_test (P, pn);
}
}
{
int i;
fprintf (out, "%snn", _("Useless rules:"));
fputs ("nn", out);
}
}
fprintf (out, "nn");
fprintf (out, "Rulesn-----nn");
fprintf (out, "Num (Prec, Assoc, Useful, Ritem Range) Lhs -> Rhs (Ritem range) [Num]n");
{
int rhs_count = 0;
/* Find the last RHS index in ritems. */
}
fprintf (out, "nn");
fprintf (out, "Rules interpretedn-----------------nn");
{
fprintf (out, "%-5d  %s :", i, symbols[rules[i].lhs]->tag);
for (r = rules[i].rhs; *r >= 0; r++)
## ------------------- ##
## Underivable Rules.  ##
## ------------------- ##