mirror of
https://git.savannah.gnu.org/git/bison.git
synced 2026-03-10 12:53:03 +00:00
5844cd0cfa
removal of useless rules via CPP but via `if (0)', so that the compiler still check the code is valid. For instance, it should have noticed `rline' no longer exists: use the `line' member of rule_t. * src/gram.c (dummy, rline): Remove, unused.
581 lines
15 KiB
C
581 lines
15 KiB
C
/* Grammar reduction for Bison.
|
||
Copyright 1988, 1989, 2000, 2001 Free Software Foundation, Inc.
|
||
|
||
This file is part of Bison, the GNU Compiler Compiler.
|
||
|
||
Bison is free software; you can redistribute it and/or modify
|
||
it under the terms of the GNU General Public License as published by
|
||
the Free Software Foundation; either version 2, or (at your option)
|
||
any later version.
|
||
|
||
Bison is distributed in the hope that it will be useful,
|
||
but WITHOUT ANY WARRANTY; without even the implied warranty of
|
||
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
||
GNU General Public License for more details.
|
||
|
||
You should have received a copy of the GNU General Public License
|
||
along with Bison; see the file COPYING. If not, write to
|
||
the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
|
||
Boston, MA 02111-1307, USA. */
|
||
|
||
|
||
/* Reduce the grammar: Find and eliminate unreachable terminals,
|
||
nonterminals, and productions. David S. Bakin. */
|
||
|
||
/* Don't eliminate unreachable terminals: They may be used by the
|
||
user's parser. */
|
||
|
||
#include "system.h"
|
||
#include "getargs.h"
|
||
#include "files.h"
|
||
#include "gram.h"
|
||
#include "complain.h"
|
||
#include "reduce.h"
|
||
#include "reader.h"
|
||
#include "getargs.h"
|
||
|
||
typedef unsigned *BSet;
|
||
typedef short *rule;
|
||
|
||
|
||
/* Set of all nonterminals which are not useless. */
|
||
static BSet N;
|
||
|
||
/* Set of all rules which have no useless nonterminals in their RHS. */
|
||
static BSet P;
|
||
|
||
/* Set of all accessible symbols. */
|
||
static BSet V;
|
||
|
||
/* Set of symbols used to define rule precedence (so they are
|
||
`useless', but no warning should be issued). */
|
||
static BSet V1;
|
||
|
||
static int nuseful_productions;
|
||
static int nuseless_productions;
|
||
static int nuseful_nonterminals;
|
||
int nuseless_nonterminals;
|
||
|
||
static bool
|
||
bits_equal (BSet L, BSet R, int n)
|
||
{
|
||
int i;
|
||
|
||
for (i = n - 1; i >= 0; i--)
|
||
if (L[i] != R[i])
|
||
return FALSE;
|
||
return TRUE;
|
||
}
|
||
|
||
|
||
static int
|
||
nbits (unsigned i)
|
||
{
|
||
int count = 0;
|
||
|
||
while (i != 0)
|
||
{
|
||
i ^= (i & ((unsigned) (-(int) i)));
|
||
++count;
|
||
}
|
||
return count;
|
||
}
|
||
|
||
|
||
static int
|
||
bits_size (BSet S, int n)
|
||
{
|
||
int i, count = 0;
|
||
|
||
for (i = n - 1; i >= 0; i--)
|
||
count += nbits (S[i]);
|
||
return count;
|
||
}
|
||
|
||
/*-------------------------------------------------------------------.
|
||
| Another way to do this would be with a set for each production and |
|
||
| then do subset tests against N0, but even for the C grammar the |
|
||
| whole reducing process takes only 2 seconds on my 8Mhz AT. |
|
||
`-------------------------------------------------------------------*/
|
||
|
||
static bool
|
||
useful_production (int i, BSet N0)
|
||
{
|
||
rule r;
|
||
short n;
|
||
|
||
/* A production is useful if all of the nonterminals in its appear
|
||
in the set of useful nonterminals. */
|
||
|
||
for (r = &ritem[rule_table[i].rhs]; *r > 0; r++)
|
||
if (ISVAR (n = *r))
|
||
if (!BITISSET (N0, n - ntokens))
|
||
return FALSE;
|
||
return TRUE;
|
||
}
|
||
|
||
|
||
/*---------------------------------------------------------.
|
||
| Remember that rules are 1-origin, symbols are 0-origin. |
|
||
`---------------------------------------------------------*/
|
||
|
||
static void
|
||
useless_nonterminals (void)
|
||
{
|
||
BSet Np, Ns;
|
||
int i;
|
||
|
||
/* N is set as built. Np is set being built this iteration. P is
|
||
set of all productions which have a RHS all in N. */
|
||
|
||
Np = XCALLOC (unsigned, WORDSIZE (nvars));
|
||
|
||
/* The set being computed is a set of nonterminals which can derive
|
||
the empty string or strings consisting of all terminals. At each
|
||
iteration a nonterminal is added to the set if there is a
|
||
production with that nonterminal as its LHS for which all the
|
||
nonterminals in its RHS are already in the set. Iterate until
|
||
the set being computed remains unchanged. Any nonterminals not
|
||
in the set at that point are useless in that they will never be
|
||
used in deriving a sentence of the language.
|
||
|
||
This iteration doesn't use any special traversal over the
|
||
productions. A set is kept of all productions for which all the
|
||
nonterminals in the RHS are in useful. Only productions not in
|
||
this set are scanned on each iteration. At the end, this set is
|
||
saved to be used when finding useful productions: only
|
||
productions in this set will appear in the final grammar. */
|
||
|
||
while (1)
|
||
{
|
||
for (i = WORDSIZE (nvars) - 1; i >= 0; i--)
|
||
Np[i] = N[i];
|
||
for (i = 1; i <= nrules; i++)
|
||
{
|
||
if (!BITISSET (P, i))
|
||
{
|
||
if (useful_production (i, N))
|
||
{
|
||
SETBIT (Np, rule_table[i].lhs - ntokens);
|
||
SETBIT (P, i);
|
||
}
|
||
}
|
||
}
|
||
if (bits_equal (N, Np, WORDSIZE (nvars)))
|
||
break;
|
||
Ns = Np;
|
||
Np = N;
|
||
N = Ns;
|
||
}
|
||
XFREE (N);
|
||
N = Np;
|
||
}
|
||
|
||
|
||
static void
|
||
inaccessable_symbols (void)
|
||
{
|
||
BSet Vp, Vs, Pp;
|
||
int i;
|
||
short t;
|
||
rule r;
|
||
|
||
/* Find out which productions are reachable and which symbols are
|
||
used. Starting with an empty set of productions and a set of
|
||
symbols which only has the start symbol in it, iterate over all
|
||
productions until the set of productions remains unchanged for an
|
||
iteration. For each production which has a LHS in the set of
|
||
reachable symbols, add the production to the set of reachable
|
||
productions, and add all of the nonterminals in the RHS of the
|
||
production to the set of reachable symbols.
|
||
|
||
Consider only the (partially) reduced grammar which has only
|
||
nonterminals in N and productions in P.
|
||
|
||
The result is the set P of productions in the reduced grammar,
|
||
and the set V of symbols in the reduced grammar.
|
||
|
||
Although this algorithm also computes the set of terminals which
|
||
are reachable, no terminal will be deleted from the grammar. Some
|
||
terminals might not be in the grammar but might be generated by
|
||
semantic routines, and so the user might want them available with
|
||
specified numbers. (Is this true?) However, the nonreachable
|
||
terminals are printed (if running in verbose mode) so that the
|
||
user can know. */
|
||
|
||
Vp = XCALLOC (unsigned, WORDSIZE (nsyms));
|
||
Pp = XCALLOC (unsigned, WORDSIZE (nrules + 1));
|
||
|
||
/* If the start symbol isn't useful, then nothing will be useful. */
|
||
if (BITISSET (N, start_symbol - ntokens))
|
||
{
|
||
SETBIT (V, start_symbol);
|
||
|
||
while (1)
|
||
{
|
||
for (i = WORDSIZE (nsyms) - 1; i >= 0; i--)
|
||
Vp[i] = V[i];
|
||
for (i = 1; i <= nrules; i++)
|
||
{
|
||
if (!BITISSET (Pp, i)
|
||
&& BITISSET (P, i)
|
||
&& BITISSET (V, rule_table[i].lhs))
|
||
{
|
||
for (r = &ritem[rule_table[i].rhs]; *r >= 0; r++)
|
||
if (ISTOKEN (t = *r) || BITISSET (N, t - ntokens))
|
||
SETBIT (Vp, t);
|
||
SETBIT (Pp, i);
|
||
}
|
||
}
|
||
if (bits_equal (V, Vp, WORDSIZE (nsyms)))
|
||
break;
|
||
Vs = Vp;
|
||
Vp = V;
|
||
V = Vs;
|
||
}
|
||
}
|
||
|
||
XFREE (V);
|
||
V = Vp;
|
||
|
||
/* Tokens 0, 1, and 2 are internal to Bison. Consider them useful. */
|
||
SETBIT (V, 0); /* end-of-input token */
|
||
SETBIT (V, 1); /* error token */
|
||
SETBIT (V, 2); /* some undefined token */
|
||
|
||
XFREE (P);
|
||
P = Pp;
|
||
|
||
nuseful_productions = bits_size (P, WORDSIZE (nrules + 1));
|
||
nuseless_productions = nrules - nuseful_productions;
|
||
|
||
nuseful_nonterminals = 0;
|
||
for (i = ntokens; i < nsyms; i++)
|
||
if (BITISSET (V, i))
|
||
nuseful_nonterminals++;
|
||
nuseless_nonterminals = nvars - nuseful_nonterminals;
|
||
|
||
/* A token that was used in %prec should not be warned about. */
|
||
for (i = 1; i < nrules; i++)
|
||
if (rule_table[i].precsym != 0)
|
||
SETBIT (V1, rule_table[i].precsym);
|
||
}
|
||
|
||
static void
|
||
reduce_grammar_tables (void)
|
||
{
|
||
/* This is turned off because we would need to change the numbers in
|
||
the case statements in the actions file.
|
||
|
||
We don't disable it via CPP so that it is still checked with the
|
||
rest of the code, to avoid its becoming completely obsolete.
|
||
|
||
FIXME: I think the comment above demonstrates this code must be
|
||
turned off for *semantic* parser, not in the general case. Try
|
||
to understand this better --akim. */
|
||
|
||
if (0)
|
||
/* remove useless productions */
|
||
if (nuseless_productions > 0)
|
||
{
|
||
short np, pn, ni, pi;
|
||
|
||
np = 0;
|
||
ni = 0;
|
||
for (pn = 1; pn <= nrules; pn++)
|
||
if (BITISSET (P, pn))
|
||
{
|
||
np++;
|
||
if (pn != np)
|
||
{
|
||
rule_table[np].lhs = rule_table[pn].lhs;
|
||
rule_table[np].line = rule_table[pn].line;
|
||
rule_table[np].prec = rule_table[pn].prec;
|
||
rule_table[np].assoc = rule_table[pn].assoc;
|
||
rule_table[np].rhs = rule_table[pn].rhs;
|
||
if (rule_table[np].rhs != ni)
|
||
{
|
||
pi = rule_table[np].rhs;
|
||
rule_table[np].rhs = ni;
|
||
while (ritem[pi] >= 0)
|
||
ritem[ni++] = ritem[pi++];
|
||
ritem[ni++] = -np;
|
||
}
|
||
}
|
||
else
|
||
{
|
||
while (ritem[ni++] >= 0);
|
||
}
|
||
}
|
||
|
||
ritem[ni] = 0;
|
||
nrules -= nuseless_productions;
|
||
nitems = ni;
|
||
|
||
/* Is it worth it to reduce the amount of memory for the
|
||
grammar? Probably not. */
|
||
}
|
||
|
||
/* Disable useless productions. */
|
||
if (nuseless_productions > 0)
|
||
{
|
||
int pn;
|
||
for (pn = 1; pn <= nrules; pn++)
|
||
rule_table[pn].useful = BITISSET (P, pn);
|
||
}
|
||
}
|
||
|
||
|
||
/*------------------------------.
|
||
| Remove useless nonterminals. |
|
||
`------------------------------*/
|
||
|
||
static void
|
||
nonterminals_reduce (void)
|
||
{
|
||
int i, n;
|
||
rule r;
|
||
|
||
/* Map the nonterminals to their new index: useful first, useless
|
||
afterwards. Kept for later report. */
|
||
|
||
short *nontermmap = XCALLOC (short, nvars) - ntokens;
|
||
n = ntokens;
|
||
for (i = ntokens; i < nsyms; i++)
|
||
if (BITISSET (V, i))
|
||
nontermmap[i] = n++;
|
||
for (i = ntokens; i < nsyms; i++)
|
||
if (!BITISSET (V, i))
|
||
nontermmap[i] = n++;
|
||
|
||
|
||
/* Shuffle elements of tables indexed by symbol number. */
|
||
{
|
||
short *sassoc_sorted = XMALLOC (short, nvars) - ntokens;
|
||
short *sprec_sorted = XMALLOC (short, nvars) - ntokens;
|
||
char **tags_sorted = XMALLOC (char *, nvars) - ntokens;
|
||
|
||
for (i = ntokens; i < nsyms; i++)
|
||
{
|
||
n = nontermmap[i];
|
||
sassoc_sorted[n] = sassoc[i];
|
||
sprec_sorted[n] = sprec[i];
|
||
tags_sorted[n] = tags[i];
|
||
}
|
||
for (i = ntokens; i < nsyms; i++)
|
||
{
|
||
sassoc[i] = sassoc_sorted[i];
|
||
sprec[i] = sprec_sorted[i];
|
||
tags[i] = tags_sorted[i];
|
||
}
|
||
free (sassoc_sorted + ntokens);
|
||
free (sprec_sorted + ntokens);
|
||
free (tags_sorted + ntokens);
|
||
}
|
||
|
||
/* Replace all symbol numbers in valid data structures. */
|
||
|
||
for (i = 1; i <= nrules; i++)
|
||
{
|
||
rule_table[i].lhs = nontermmap[rule_table[i].lhs];
|
||
if (ISVAR (rule_table[i].precsym))
|
||
/* Can this happen? */
|
||
rule_table[i].precsym = nontermmap[rule_table[i].precsym];
|
||
}
|
||
|
||
for (r = ritem; *r; r++)
|
||
if (ISVAR (*r))
|
||
*r = nontermmap[*r];
|
||
|
||
start_symbol = nontermmap[start_symbol];
|
||
|
||
nsyms -= nuseless_nonterminals;
|
||
nvars -= nuseless_nonterminals;
|
||
|
||
free (nontermmap + ntokens);
|
||
}
|
||
|
||
|
||
/*------------------------------------------------------------------.
|
||
| Output the detailed results of the reductions. For FILE.output. |
|
||
`------------------------------------------------------------------*/
|
||
|
||
void
|
||
reduce_output (FILE *out)
|
||
{
|
||
if (nuseless_nonterminals > 0)
|
||
{
|
||
int i;
|
||
fprintf (out, "%s\n\n", _("Useless nonterminals:"));
|
||
for (i = 0; i < nuseless_nonterminals; ++i)
|
||
fprintf (out, " %s\n", tags[nsyms + i]);
|
||
fputs ("\n\n", out);
|
||
}
|
||
|
||
{
|
||
bool b = FALSE;
|
||
int i;
|
||
for (i = 0; i < ntokens; i++)
|
||
if (!BITISSET (V, i) && !BITISSET (V1, i))
|
||
{
|
||
if (!b)
|
||
fprintf (out, "%s\n\n", _("Terminals which are not used:"));
|
||
b = TRUE;
|
||
fprintf (out, " %s\n", tags[i]);
|
||
}
|
||
if (b)
|
||
fputs ("\n\n", out);
|
||
}
|
||
|
||
if (nuseless_productions > 0)
|
||
{
|
||
int i;
|
||
fprintf (out, "%s\n\n", _("Useless rules:"));
|
||
for (i = 1; i <= nrules; i++)
|
||
if (!rule_table[i].useful)
|
||
{
|
||
rule r;
|
||
fprintf (out, "#%-4d ", i);
|
||
fprintf (out, "%s:", tags[rule_table[i].lhs]);
|
||
for (r = &ritem[rule_table[i].rhs]; *r >= 0; r++)
|
||
fprintf (out, " %s", tags[*r]);
|
||
fputs (";\n", out);
|
||
}
|
||
fputs ("\n\n", out);
|
||
}
|
||
}
|
||
|
||
static void
|
||
dump_grammar (FILE *out)
|
||
{
|
||
int i;
|
||
rule r;
|
||
|
||
fprintf (out, "REDUCED GRAMMAR\n\n");
|
||
fprintf (out,
|
||
"ntokens = %d, nvars = %d, nsyms = %d, nrules = %d, nitems = %d\n\n",
|
||
ntokens, nvars, nsyms, nrules, nitems);
|
||
fprintf (out, "Variables\n---------\n\n");
|
||
fprintf (out, "Value Sprec Sassoc Tag\n");
|
||
for (i = ntokens; i < nsyms; i++)
|
||
fprintf (out, "%5d %5d %5d %s\n", i, sprec[i], sassoc[i], tags[i]);
|
||
fprintf (out, "\n\n");
|
||
fprintf (out, "Rules\n-----\n\n");
|
||
fprintf (out, "Num (Prec, Assoc, Useful, Ritem Range) Lhs -> Rhs (Ritem range) [Num]\n");
|
||
for (i = 1; i <= nrules; i++)
|
||
{
|
||
int rhs_count = 0;
|
||
/* Find the last RHS index in ritems. */
|
||
for (r = &ritem[rule_table[i].rhs]; *r > 0; ++r)
|
||
++rhs_count;
|
||
fprintf (out, "%3d (%2d, %2d, %2d, %2d-%2d) %2d ->",
|
||
i,
|
||
rule_table[i].prec, rule_table[i].assoc, rule_table[i].useful,
|
||
rule_table[i].rhs, rule_table[i].rhs + rhs_count - 1,
|
||
rule_table[i].lhs);
|
||
/* Dumped the RHS. */
|
||
for (r = &ritem[rule_table[i].rhs]; *r > 0; r++)
|
||
fprintf (out, "%3d", *r);
|
||
fprintf (out, " [%d]\n", -(*r));
|
||
}
|
||
fprintf (out, "\n\n");
|
||
fprintf (out, "Rules interpreted\n-----------------\n\n");
|
||
for (i = 1; i <= nrules; i++)
|
||
{
|
||
fprintf (out, "%-5d %s :", i, tags[rule_table[i].lhs]);
|
||
for (r = &ritem[rule_table[i].rhs]; *r > 0; r++)
|
||
fprintf (out, " %s", tags[*r]);
|
||
fputc ('\n', out);
|
||
}
|
||
fprintf (out, "\n\n");
|
||
}
|
||
|
||
|
||
|
||
/*-------------------------------.
|
||
| Report the results to STDERR. |
|
||
`-------------------------------*/
|
||
|
||
static void
|
||
reduce_print (void)
|
||
{
|
||
if (yacc_flag && nuseless_productions)
|
||
fprintf (stderr, ngettext ("%d rule never reduced\n",
|
||
"%d rules never reduced\n",
|
||
nuseless_productions),
|
||
nuseless_productions);
|
||
|
||
fprintf (stderr, _("%s contains "), infile);
|
||
|
||
if (nuseless_nonterminals > 0)
|
||
fprintf (stderr, ngettext ("%d useless nonterminal",
|
||
"%d useless nonterminals",
|
||
nuseless_nonterminals),
|
||
nuseless_nonterminals);
|
||
|
||
if (nuseless_nonterminals > 0 && nuseless_productions > 0)
|
||
fprintf (stderr, _(" and "));
|
||
|
||
if (nuseless_productions > 0)
|
||
fprintf (stderr, ngettext ("%d useless rule",
|
||
"%d useless rules",
|
||
nuseless_productions),
|
||
nuseless_productions);
|
||
fprintf (stderr, "\n");
|
||
fflush (stderr);
|
||
}
|
||
|
||
void
|
||
reduce_grammar (void)
|
||
{
|
||
bool reduced;
|
||
|
||
/* Allocate the global sets used to compute the reduced grammar */
|
||
|
||
N = XCALLOC (unsigned, WORDSIZE (nvars));
|
||
P = XCALLOC (unsigned, WORDSIZE (nrules + 1));
|
||
V = XCALLOC (unsigned, WORDSIZE (nsyms));
|
||
V1 = XCALLOC (unsigned, WORDSIZE (nsyms));
|
||
|
||
useless_nonterminals ();
|
||
inaccessable_symbols ();
|
||
|
||
reduced = (bool) (nuseless_nonterminals + nuseless_productions > 0);
|
||
|
||
if (!reduced)
|
||
return;
|
||
|
||
reduce_print ();
|
||
|
||
if (!BITISSET (N, start_symbol - ntokens))
|
||
fatal (_("Start symbol %s does not derive any sentence"),
|
||
tags[start_symbol]);
|
||
|
||
reduce_grammar_tables ();
|
||
if (nuseless_nonterminals > 0)
|
||
nonterminals_reduce ();
|
||
|
||
if (trace_flag)
|
||
{
|
||
dump_grammar (stderr);
|
||
|
||
fprintf (stderr, "reduced %s defines %d terminals, %d nonterminals\
|
||
, and %d productions.\n",
|
||
infile, ntokens, nvars, nrules);
|
||
}
|
||
}
|
||
|
||
|
||
/*-----------------------------------------------------------.
|
||
| Free the global sets used to compute the reduced grammar. |
|
||
`-----------------------------------------------------------*/
|
||
|
||
void
|
||
reduce_free (void)
|
||
{
|
||
XFREE (N);
|
||
XFREE (V);
|
||
XFREE (V1);
|
||
XFREE (P);
|
||
}
|