/* Generate the LR(0) parser states for Bison.
Copyright (C) 1984, 1986, 1989, 2000-2002, 2004-2007, 2009-2012 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/>. */
/* See comments in state.h for the data structures that represent it.
The entry point is generate_states. */
#include <config.h>
#include "system.h"
#include <bitset.h>
#include "LR0.h"
#include "closure.h"
#include "complain.h"
#include "getargs.h"
#include "gram.h"
#include "gram.h"
#include "lalr.h"
#include "reader.h"
#include "reduce.h"
#include "state.h"
#include "symtab.h"
typedef struct state_list
{
struct state_list *next;
state *state;
} state_list;
static state_list *first_state = NULL;
static state_list *last_state = NULL;
/*------------------------------------------------------------------.
| A state was just discovered from another state. Queue it for |
| later examination, in order to find its transitions. Return it. |
`------------------------------------------------------------------*/
static state *
state_list_append (symbol_number sym, size_t core_size, item_number *core)
{
state_list *node = xmalloc (sizeof *node);
state *s = state_new (sym, core_size, core);
if (trace_flag & trace_automaton)
fprintf (stderr, "state_list_append (state = %d, symbol = %d (%s))\n",
nstates, sym, symbols[sym]->tag);
node->next = NULL;
node->state = s;
if (!first_state)
first_state = node;
if (last_state)
last_state->next = node;
last_state = node;
return s;
}
static int nshifts;
static symbol_number *shift_symbol;
static rule **redset;
static state **shiftset;
static item_number **kernel_base;
static int *kernel_size;
static item_number *kernel_items;
static void
allocate_itemsets (void)
{
symbol_number i;
rule_number r;
item_number *rhsp;
/* Count the number of occurrences of all the symbols in RITEMS.
Note that useless productions (hence useless nonterminals) are
browsed too, hence we need to allocate room for _all_ the
symbols. */
size_t count = 0;
size_t *symbol_count = xcalloc (nsyms + nuseless_nonterminals,
sizeof *symbol_count);
for (r = 0; r < nrules; ++r)
for (rhsp = rules[r].rhs; *rhsp >= 0; ++rhsp)
{
count++;
symbol_count[*rhsp]++;
}
/* See comments before new_itemsets. All the vectors of items
live inside KERNEL_ITEMS. The number of active items after
some symbol S cannot be more than the number of times that S
appears as an item, which is SYMBOL_COUNT[S].
We allocate that much space for each symbol. */
kernel_base = xnmalloc (nsyms, sizeof *kernel_base);
kernel_items = xnmalloc (count, sizeof *kernel_items);
count = 0;
for (i = 0; i < nsyms; i++)
{
kernel_base[i] = kernel_items + count;
count += symbol_count[i];
}
free (symbol_count);
kernel_size = xnmalloc (nsyms, sizeof *kernel_size);
}
static void
allocate_storage (void)
{
allocate_itemsets ();
shiftset = xnmalloc (nsyms, sizeof *shiftset);
redset = xnmalloc (nrules, sizeof *redset);
state_hash_new ();
shift_symbol = xnmalloc (nsyms, sizeof *shift_symbol);
}
static void
free_storage (void)
{
free (shift_symbol);
free (redset);
free (shiftset);
free (kernel_base);
free (kernel_size);
free (kernel_items);
state_hash_free ();
}
/*---------------------------------------------------------------.
| Find which symbols can be shifted in S, and for each one |
| record which items would be active after that shift. Uses the |
| contents of itemset. |
| |
| shift_symbol is set to a vector of the symbols that can be |
| shifted. For each symbol in the grammar, kernel_base[symbol] |
| points to a vector of item numbers activated if that symbol is |
| shifted, and kernel_size[symbol] is their numbers. |
| |
| itemset is sorted on item index in ritem, which is sorted on |
| rule number. Compute each kernel_base[symbol] with the same |
| sort. |
`---------------------------------------------------------------*/
static void
new_itemsets (state *s)
{
size_t i;
if (trace_flag & trace_automaton)
fprintf (stderr, "Entering new_itemsets, state = %d\n", s->number);
memset (kernel_size, 0, nsyms * sizeof *kernel_size);
nshifts = 0;
for (i = 0; i < nitemset; ++i)
if (item_number_is_symbol_number (ritem[itemset[i]]))
{
symbol_number sym = item_number_as_symbol_number (ritem[itemset[i]]);
if (!kernel_size[sym])
{
shift_symbol[nshifts] = sym;
nshifts++;
}
kernel_base[sym][kernel_size[sym]] = itemset[i] + 1;
kernel_size[sym]++;
}
}
/*--------------------------------------------------------------.
| Find the state we would get to (from the current state) by |
| shifting SYM. Create a new state if no equivalent one exists |
| already. Used by append_states. |
`--------------------------------------------------------------*/
static state *
get_state (symbol_number sym, size_t core_size, item_number *core)
{
state *s;
if (trace_flag & trace_automaton)
fprintf (stderr, "Entering get_state, symbol = %d (%s)\n",
sym, symbols[sym]->tag);
s = state_hash_lookup (core_size, core);
if (!s)
s = state_list_append (sym, core_size, core);
if (trace_flag & trace_automaton)
fprintf (stderr, "Exiting get_state => %d\n", s->number);
return s;
}
/*---------------------------------------------------------------.
| Use the information computed by new_itemsets to find the state |
| numbers reached by each shift transition from S. |
| |
| SHIFTSET is set up as a vector of those states. |
`---------------------------------------------------------------*/
static void
append_states (state *s)
{
int i;
if (trace_flag & trace_automaton)
fprintf (stderr, "Entering append_states, state = %d\n", s->number);
/* First sort shift_symbol into increasing order. */
for (i = 1; i < nshifts; i++)
{
symbol_number sym = shift_symbol[i];
int j;
for (j = i; 0 < j && sym < shift_symbol[j - 1]; j--)
shift_symbol[j] = shift_symbol[j - 1];
shift_symbol[j] = sym;
}
for (i = 0; i < nshifts; i++)
{
symbol_number sym = shift_symbol[i];
shiftset[i] = get_state (sym, kernel_size[sym], kernel_base[sym]);
}
}
/*----------------------------------------------------------------.
| Find which rules can be used for reduction transitions from the |
| current state and make a reductions structure for the state to |
| record their rule numbers. |
`----------------------------------------------------------------*/
static void
save_reductions (state *s)
{
int count = 0;
size_t i;
/* Find and count the active items that represent ends of rules. */
for (i = 0; i < nitemset; ++i)
{
item_number item = ritem[itemset[i]];
if (item_number_is_rule_number (item))
{
rule_number r = item_number_as_rule_number (item);
redset[count++] = &rules[r];
if (r == 0)
{
/* This is "reduce 0", i.e., accept. */
aver (!final_state);
final_state = s;
}
}
}
/* Make a reductions structure and copy the data into it. */
state_reductions_set (s, count, redset);
}
/*---------------.
| Build STATES. |
`---------------*/
static void
set_states (void)
{
states = xcalloc (nstates, sizeof *states);
while (first_state)
{
state_list *this = first_state;
/* Pessimization, but simplification of the code: make sure all
the states have valid transitions and reductions members,
even if reduced to 0. It is too soon for errs, which are
computed later, but set_conflicts. */
state *s = this->state;
if (!s->transitions)
state_transitions_set (s, 0, 0);
if (!s->reductions)
state_reductions_set (s, 0, 0);
states[s->number] = s;
first_state = this->next;
free (this);
}
first_state = NULL;
last_state = NULL;
}
/*-------------------------------------------------------------------.
| Compute the LR(0) parser states (see state.h for details) from the |
| grammar. |
`-------------------------------------------------------------------*/
void
generate_states (void)
{
item_number initial_core = 0;
state_list *list = NULL;
allocate_storage ();
new_closure (nritems);
/* Create the initial state. The 0 at the lhs is the index of the
item of this initial rule. */
state_list_append (0, 1, &initial_core);
/* States are queued when they are created; process them all. */
for (list = first_state; list; list = list->next)
{
state *s = list->state;
if (trace_flag & trace_automaton)
fprintf (stderr, "Processing state %d (reached by %s)\n",
s->number,
symbols[s->accessing_symbol]->tag);
/* Set up itemset for the transitions out of this state. itemset gets a
vector of all the items that could be accepted next. */
closure (s->items, s->nitems);
/* Record the reductions allowed out of this state. */
save_reductions (s);
/* Find the itemsets of the states that shifts can reach. */
new_itemsets (s);
/* Find or create the core structures for those states. */
append_states (s);
/* Create the shifts structures for the shifts to those states,
now that the state numbers transitioning to are known. */
state_transitions_set (s, nshifts, shiftset);
}
/* discard various storage */
free_closure ();
free_storage ();
/* Set up STATES. */
set_states ();
}