/* Compute lookahead criteria for Bison.
- Copyright (C) 1984, 1986, 1989, 2000, 2001, 2002, 2003, 2004, 2005,
- 2006, 2007 Free Software Foundation, Inc.
+ Copyright (C) 1984, 1986, 1989, 2000-2012 Free Software Foundation,
+ Inc.
This file is part of Bison, the GNU Compiler Compiler.
along with this program. If not, see <http://www.gnu.org/licenses/>. */
-/* Compute how to make the finite state machine deterministic; find
- which rules need lookahead in each state, and which lookahead
+/* Find which rules need lookahead in each state, and which lookahead
tokens they accept. */
#include <config.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;
-static goto_number ngotos;
+goto_number ngotos;
state_number *from_state;
state_number *to_state;
+bitsetv goto_follows = NULL;
/* Linked list of goto numbers. */
typedef struct goto_list
size_t nLA;
-/* And for the famous F variable, which name is so descriptive that a
- comment is hardly needed. <grin>. */
-static bitsetv F = NULL;
-
static goto_number **includes;
static goto_list **lookback;
-static void
+void
set_goto_map (void)
{
state_number s;
}
-
-/*----------------------------------------------------------.
-| Map a state/symbol pair into its numeric representation. |
-`----------------------------------------------------------*/
-
-static goto_number
+goto_number
map_goto (state_number s0, symbol_number sym)
{
goto_number high;
goto_number i;
- F = bitsetv_create (ngotos, ntokens, BITSET_FIXED);
+ goto_follows = bitsetv_create (ngotos, ntokens, BITSET_FIXED);
for (i = 0; i < ngotos; i++)
{
int j;
FOR_EACH_SHIFT (sp, j)
- bitset_set (F[i], TRANSITION_SYMBOL (sp, j));
+ bitset_set (goto_follows[i], TRANSITION_SYMBOL (sp, j));
for (; j < sp->num; j++)
{
}
}
- relation_digraph (reads, ngotos, &F);
+ relation_digraph (reads, ngotos, &goto_follows);
for (i = 0; i < ngotos; i++)
free (reads[i]);
{
done = true;
/* Each rhs ends in a rule number, and there is a
- sentinel before the first rhs, so it is safe to
+ sentinel (ritem[-1]=0) before the first rhs, so it is safe to
decrement RP here. */
rp--;
if (ISVAR (*rp))
{
goto_number i;
- relation_digraph (includes, ngotos, &F);
+ relation_digraph (includes, ngotos, &goto_follows);
for (i = 0; i < ngotos; i++)
free (includes[i]);
for (i = 0; i < nLA; i++)
for (sp = lookback[i]; sp; sp = sp->next)
- bitset_or (LA[i], LA[i], F[sp->value]);
+ 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);
- bitsetv_free (F);
}
`----------------------------------------------------*/
static int
-state_lookahead_tokens_count (state *s)
+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;
- /* 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'. There is no need to check that
- transition 0 hasn't been disabled before checking if it is a
- shift since transitions are only disabled during conflict
- resolution, and that hasn't happened yet. */
+ /* 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 && 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;
| Compute LA, NLA, and the lookahead_tokens members. |
`----------------------------------------------------*/
-static void
+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]);
+ 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);
- lookback = xcalloc (nLA, sizeof *lookback);
/* 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]);
+ int count =
+ state_lookahead_tokens_count (states[i],
+ default_reduction_only_for_accept);
if (count)
{
states[i]->reductions->lookahead_tokens = pLA;
initialize_LA ();
set_goto_map ();
initialize_F ();
+ lookback = xcalloc (nLA, sizeof *lookback);
build_relations ();
compute_FOLLOWS ();
compute_lookahead_tokens ();
projects / bison.git / blobdiff