X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/f16b08196c780556cbf50691e2944960aebc46f6..8d90395dd7aa01e6616cb46eddc1dbddafd8d9ee:/src/lalr.c?ds=sidebyside diff --git a/src/lalr.c b/src/lalr.c index 15213422..fbd2800f 100644 --- a/src/lalr.c +++ b/src/lalr.c @@ -1,7 +1,7 @@ /* Compute lookahead criteria for Bison. Copyright (C) 1984, 1986, 1989, 2000, 2001, 2002, 2003, 2004, 2005, - 2006, 2007 Free Software Foundation, Inc. + 2006, 2007, 2008, 2009 Free Software Foundation, Inc. This file is part of Bison, the GNU Compiler Compiler. @@ -36,15 +36,17 @@ #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 @@ -63,17 +65,13 @@ static bitsetv LA = NULL; size_t nLA; -/* And for the famous F variable, which name is so descriptive that a - comment is hardly needed. . */ -static bitsetv F = NULL; - static goto_number **includes; static goto_list **lookback; -static void +void set_goto_map (void) { state_number s; @@ -133,12 +131,7 @@ set_goto_map (void) } - -/*----------------------------------------------------------. -| 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; @@ -173,7 +166,7 @@ initialize_F (void) goto_number i; - F = bitsetv_create (ngotos, ntokens, BITSET_FIXED); + goto_follows = bitsetv_create (ngotos, ntokens, BITSET_FIXED); for (i = 0; i < ngotos; i++) { @@ -182,7 +175,7 @@ initialize_F (void) 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++) { @@ -202,7 +195,7 @@ initialize_F (void) } } - relation_digraph (reads, ngotos, &F); + relation_digraph (reads, ngotos, &goto_follows); for (i = 0; i < ngotos; i++) free (reads[i]); @@ -262,8 +255,8 @@ build_relations (void) while (!done) { done = true; - /* Each rhs ends in an item number, and there is a - sentinel before the first rhs, so it is safe to + /* 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)) @@ -302,7 +295,7 @@ compute_FOLLOWS (void) { goto_number i; - relation_digraph (includes, ngotos, &F); + relation_digraph (includes, ngotos, &goto_follows); for (i = 0; i < ngotos; i++) free (includes[i]); @@ -319,14 +312,13 @@ compute_lookahead_tokens (void) 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); } @@ -336,22 +328,31 @@ compute_lookahead_tokens (void) `----------------------------------------------------*/ 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; @@ -364,28 +365,39 @@ state_lookahead_tokens_count (state *s) | 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; @@ -437,6 +449,7 @@ lalr (void) initialize_LA (); set_goto_map (); initialize_F (); + lookback = xcalloc (nLA, sizeof *lookback); build_relations (); compute_FOLLOWS (); compute_lookahead_tokens ();