/* Compute lookahead criteria for Bison.
Copyright (C) 1984, 1986, 1989, 2000-2012 Free Software Foundation,
Inc.
This file is part of Bison, the GNU Compiler Compiler.
This program 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 3 of the License, or
(at your option) any later version.
This program 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 this program. If not, see <http://www.gnu.org/licenses/>. */
/* Find which rules need lookahead in each state, and which lookahead
tokens they accept. */
#include <config.h>
#include "system.h"
#include <bitset.h>
#include <bitsetv.h>
#include "LR0.h"
#include "complain.h"
#include "derives.h"
#include "getargs.h"
#include "gram.h"
#include "lalr.h"
#include "muscle-tab.h"
#include "nullable.h"
#include "reader.h"
#include "relation.h"
#include "symtab.h"
goto_number *goto_map;
goto_number ngotos;
state_number *from_state;
state_number *to_state;
bitsetv goto_follows = NULL;
/* Linked list of goto numbers. */
typedef struct goto_list
{
struct goto_list *next;
goto_number value;
} goto_list;
/* LA is an NLA by NTOKENS matrix of bits. LA[l, i] is 1 if the rule
LArule[l] is applicable in the appropriate state when the next
token is symbol i. If LA[l, i] and LA[l, j] are both 1 for i != j,
it is a conflict. */
static bitsetv LA = NULL;
size_t nLA;
static goto_number **includes;
static goto_list **lookback;
void
set_goto_map (void)
{
state_number s;
goto_number *temp_map;
goto_map = xcalloc (nvars + 1, sizeof *goto_map);
temp_map = xnmalloc (nvars + 1, sizeof *temp_map);
ngotos = 0;
for (s = 0; s < nstates; ++s)
{
transitions *sp = states[s]->transitions;
int i;
for (i = sp->num - 1; i >= 0 && TRANSITION_IS_GOTO (sp, i); --i)
{
ngotos++;
/* Abort if (ngotos + 1) would overflow. */
aver (ngotos != GOTO_NUMBER_MAXIMUM);
goto_map[TRANSITION_SYMBOL (sp, i) - ntokens]++;
}
}
{
goto_number k = 0;
int i;
for (i = ntokens; i < nsyms; i++)
{
temp_map[i - ntokens] = k;
k += goto_map[i - ntokens];
}
for (i = ntokens; i < nsyms; i++)
goto_map[i - ntokens] = temp_map[i - ntokens];
goto_map[nsyms - ntokens] = ngotos;
temp_map[nsyms - ntokens] = ngotos;
}
from_state = xcalloc (ngotos, sizeof *from_state);
to_state = xcalloc (ngotos, sizeof *to_state);
for (s = 0; s < nstates; ++s)
{
transitions *sp = states[s]->transitions;
int i;
for (i = sp->num - 1; i >= 0 && TRANSITION_IS_GOTO (sp, i); --i)
{
goto_number k = temp_map[TRANSITION_SYMBOL (sp, i) - ntokens]++;
from_state[k] = s;
to_state[k] = sp->states[i]->number;
}
}
free (temp_map);
}
goto_number
map_goto (state_number s0, symbol_number sym)
{
goto_number high;
goto_number low;
goto_number middle;
state_number s;
low = goto_map[sym - ntokens];
high = goto_map[sym - ntokens + 1] - 1;
for (;;)
{
aver (low <= high);
middle = (low + high) / 2;
s = from_state[middle];
if (s == s0)
return middle;
else if (s < s0)
low = middle + 1;
else
high = middle - 1;
}
}
static void
initialize_F (void)
{
goto_number **reads = xnmalloc (ngotos, sizeof *reads);
goto_number *edge = xnmalloc (ngotos + 1, sizeof *edge);
goto_number nedges = 0;
goto_number i;
goto_follows = bitsetv_create (ngotos, ntokens, BITSET_FIXED);
for (i = 0; i < ngotos; i++)
{
state_number stateno = to_state[i];
transitions *sp = states[stateno]->transitions;
int j;
FOR_EACH_SHIFT (sp, j)
bitset_set (goto_follows[i], TRANSITION_SYMBOL (sp, j));
for (; j < sp->num; j++)
{
symbol_number sym = TRANSITION_SYMBOL (sp, j);
if (nullable[sym - ntokens])
edge[nedges++] = map_goto (stateno, sym);
}
if (nedges == 0)
reads[i] = NULL;
else
{
reads[i] = xnmalloc (nedges + 1, sizeof reads[i][0]);
memcpy (reads[i], edge, nedges * sizeof edge[0]);
reads[i][nedges] = END_NODE;
nedges = 0;
}
}
relation_digraph (reads, ngotos, &goto_follows);
for (i = 0; i < ngotos; i++)
free (reads[i]);
free (reads);
free (edge);
}
static void
add_lookback_edge (state *s, rule *r, goto_number gotono)
{
int ri = state_reduction_find (s, r);
goto_list *sp = xmalloc (sizeof *sp);
sp->next = lookback[(s->reductions->lookahead_tokens - LA) + ri];
sp->value = gotono;
lookback[(s->reductions->lookahead_tokens - LA) + ri] = sp;
}
static void
build_relations (void)
{
goto_number *edge = xnmalloc (ngotos + 1, sizeof *edge);
state_number *states1 = xnmalloc (ritem_longest_rhs () + 1, sizeof *states1);
goto_number i;
includes = xnmalloc (ngotos, sizeof *includes);
for (i = 0; i < ngotos; i++)
{
int nedges = 0;
symbol_number symbol1 = states[to_state[i]]->accessing_symbol;
rule **rulep;
for (rulep = derives[symbol1 - ntokens]; *rulep; rulep++)
{
bool done;
int length = 1;
item_number const *rp;
state *s = states[from_state[i]];
states1[0] = s->number;
for (rp = (*rulep)->rhs; ! item_number_is_rule_number (*rp); rp++)
{
s = transitions_to (s->transitions,
item_number_as_symbol_number (*rp));
states1[length++] = s->number;
}
if (!s->consistent)
add_lookback_edge (s, *rulep, i);
length--;
done = false;
while (!done)
{
done = true;
/* Each rhs ends in a rule number, and there is a
sentinel (ritem[-1]=0) before the first rhs, so it is safe to
decrement RP here. */
rp--;
if (ISVAR (*rp))
{
/* Downcasting from item_number to symbol_number. */
edge[nedges++] = map_goto (states1[--length],
item_number_as_symbol_number (*rp));
if (nullable[*rp - ntokens])
done = false;
}
}
}
if (nedges == 0)
includes[i] = NULL;
else
{
int j;
includes[i] = xnmalloc (nedges + 1, sizeof includes[i][0]);
for (j = 0; j < nedges; j++)
includes[i][j] = edge[j];
includes[i][nedges] = END_NODE;
}
}
free (edge);
free (states1);
relation_transpose (&includes, ngotos);
}
static void
compute_FOLLOWS (void)
{
goto_number i;
relation_digraph (includes, ngotos, &goto_follows);
for (i = 0; i < ngotos; i++)
free (includes[i]);
free (includes);
}
static void
compute_lookahead_tokens (void)
{
size_t i;
goto_list *sp;
for (i = 0; i < nLA; i++)
for (sp = lookback[i]; sp; sp = sp->next)
bitset_or (LA[i], LA[i], goto_follows[sp->value]);
/* Free LOOKBACK. */
for (i = 0; i < nLA; i++)
LIST_FREE (goto_list, lookback[i]);
free (lookback);
}
/*----------------------------------------------------.
| Count the number of lookahead tokens required for S |
| (N_LOOKAHEAD_TOKENS member). |
`----------------------------------------------------*/
static int
state_lookahead_tokens_count (state *s, bool default_reduction_only_for_accept)
{
int n_lookahead_tokens = 0;
reductions *rp = s->reductions;
transitions *sp = s->transitions;
/* Transitions are only disabled during conflict resolution, and that
hasn't happened yet, so there should be no need to check that
transition 0 hasn't been disabled before checking if it is a shift.
However, this check was performed at one time, so we leave it as an
aver. */
aver (sp->num == 0 || !TRANSITION_IS_DISABLED (sp, 0));
/* We need a lookahead either to distinguish different reductions
(i.e., there are two or more), or to distinguish a reduction from a
shift. Otherwise, it is straightforward, and the state is
`consistent'. However, do not treat a state with any reductions as
consistent unless it is the accepting state (because there is never
a lookahead token that makes sense there, and so no lookahead token
should be read) if the user has otherwise disabled default
reductions. */
if (rp->num > 1
|| (rp->num == 1 && sp->num && TRANSITION_IS_SHIFT (sp, 0))
|| (rp->num == 1 && rp->rules[0]->number != 0
&& default_reduction_only_for_accept))
n_lookahead_tokens += rp->num;
else
s->consistent = 1;
return n_lookahead_tokens;
}
/*----------------------------------------------------.
| Compute LA, NLA, and the lookahead_tokens members. |
`----------------------------------------------------*/
void
initialize_LA (void)
{
state_number i;
bitsetv pLA;
bool default_reduction_only_for_accept;
{
char *default_reductions =
muscle_percent_define_get ("lr.default-reductions");
default_reduction_only_for_accept =
0 == strcmp (default_reductions, "accepting");
free (default_reductions);
}
/* Compute the total number of reductions requiring a lookahead. */
nLA = 0;
for (i = 0; i < nstates; i++)
nLA +=
state_lookahead_tokens_count (states[i],
default_reduction_only_for_accept);
/* Avoid having to special case 0. */
if (!nLA)
nLA = 1;
pLA = LA = bitsetv_create (nLA, ntokens, BITSET_FIXED);
/* Initialize the members LOOKAHEAD_TOKENS for each state whose reductions
require lookahead tokens. */
for (i = 0; i < nstates; i++)
{
int count =
state_lookahead_tokens_count (states[i],
default_reduction_only_for_accept);
if (count)
{
states[i]->reductions->lookahead_tokens = pLA;
pLA += count;
}
}
}
/*---------------------------------------------.
| Output the lookahead tokens for each state. |
`---------------------------------------------*/
static void
lookahead_tokens_print (FILE *out)
{
state_number i;
int j, k;
fprintf (out, "Lookahead tokens: BEGIN\n");
for (i = 0; i < nstates; ++i)
{
reductions *reds = states[i]->reductions;
bitset_iterator iter;
int n_lookahead_tokens = 0;
if (reds->lookahead_tokens)
for (k = 0; k < reds->num; ++k)
if (reds->lookahead_tokens[k])
++n_lookahead_tokens;
fprintf (out, "State %d: %d lookahead tokens\n",
i, n_lookahead_tokens);
if (reds->lookahead_tokens)
for (j = 0; j < reds->num; ++j)
BITSET_FOR_EACH (iter, reds->lookahead_tokens[j], k, 0)
{
fprintf (out, " on %d (%s) -> rule %d\n",
k, symbols[k]->tag,
reds->rules[j]->number);
};
}
fprintf (out, "Lookahead tokens: END\n");
}
void
lalr (void)
{
initialize_LA ();
set_goto_map ();
initialize_F ();
lookback = xcalloc (nLA, sizeof *lookback);
build_relations ();
compute_FOLLOWS ();
compute_lookahead_tokens ();
if (trace_flag & trace_sets)
lookahead_tokens_print (stderr);
}
void
lalr_update_state_numbers (state_number old_to_new[], state_number nstates_old)
{
goto_number ngotos_reachable = 0;
symbol_number nonterminal = 0;
aver (nsyms == nvars + ntokens);
{
goto_number i;
for (i = 0; i < ngotos; ++i)
{
while (i == goto_map[nonterminal])
goto_map[nonterminal++] = ngotos_reachable;
/* If old_to_new[from_state[i]] = nstates_old, remove this goto
entry. */
if (old_to_new[from_state[i]] != nstates_old)
{
/* from_state[i] is not removed, so it and thus to_state[i] are
reachable, so to_state[i] != nstates_old. */
aver (old_to_new[to_state[i]] != nstates_old);
from_state[ngotos_reachable] = old_to_new[from_state[i]];
to_state[ngotos_reachable] = old_to_new[to_state[i]];
++ngotos_reachable;
}
}
}
while (nonterminal <= nvars)
{
aver (ngotos == goto_map[nonterminal]);
goto_map[nonterminal++] = ngotos_reachable;
}
ngotos = ngotos_reachable;
}
void
lalr_free (void)
{
state_number s;
for (s = 0; s < nstates; ++s)
states[s]->reductions->lookahead_tokens = NULL;
bitsetv_free (LA);
}