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Re: [PATCH] cex: Fix state-item pruning
From: |
Akim Demaille |
Subject: |
Re: [PATCH] cex: Fix state-item pruning |
Date: |
Sun, 24 Jan 2021 08:04:39 +0100 |
Hi Vincent,
> Le 23 janv. 2021 à 19:25, Vincent Imbimbo <vmi6@cornell.edu> a écrit :
>
> There were several bugs in pruning that would leave the state-item graph in
> an inconsistent state which could cause crashes later on:
> * Pruning now happens in one pass instead of two.
> * Disabled state-items no longer prune the state-items they transition to if
> that state-item has other states that transition to it.
> * State-items that transition to disabled state-items are always pruned even
> if they have productions.
Wonderful! Thanks a lot for this. There's no way I could have found the right
fix...
I'm installing your fix as follows, in the maint branch for 3.7.5.
Cheers!
commit 3b94105d213795ec4a2614e24abae970b6f4a7a1
Author: Vincent Imbimbo <vmi6@cornell.edu>
Date: Sat Jan 23 13:25:18 2021 -0500
cex: fix state-item pruning
There were several bugs in pruning that would leave the state-item
graph in an inconsistent state which could cause crashes later on:
- Pruning now happens in one pass instead of two.
- Disabled state-items no longer prune the state-items they transition
to if that state-item has other states that transition to it.
- State-items that transition to disabled state-items are always
pruned even if they have productions.
Reported by Michal Bartkowiak <michal.bartkowiak@nokia.com>
https://lists.gnu.org/r/bug-bison/2021-01/msg00000.html
and Zartaj Majeed
https://github.com/akimd/bison/issues/71
* src/state-item.c (prune_forward, prune_backward): Fuse into...
(prune_state_item): this.
Adjust callers.
diff --git a/NEWS b/NEWS
index 4664e401c..720f2b1db 100644
--- a/NEWS
+++ b/NEWS
@@ -4,7 +4,11 @@ GNU Bison NEWS
** Bug fixes
-*** Fix table generation
+*** Counterexample Generation
+
+ In some cases counterexample generation could crash. This is fixed.
+
+*** Fix Table Generation
In some very rare conditions, when there are many useless tokens, it was
possible to generate incorrect parsers.
diff --git a/src/state-item.c b/src/state-item.c
index d8957c8eb..a2e0f9575 100644
--- a/src/state-item.c
+++ b/src/state-item.c
@@ -384,11 +384,10 @@ disable_state_item (state_item *si)
bitset_free (si->prods);
}
-/* disable all transitions and productions that can only be
- * reached through this state_item.
- */
+/* Disable all state_item paths that lead to/from SI and nowhere
+ else. */
static void
-prune_forward (const state_item *si)
+prune_state_item (const state_item *si)
{
state_item_list queue =
gl_list_create (GL_LINKED_LIST, NULL, NULL, NULL, true, 1,
@@ -398,8 +397,16 @@ prune_forward (const state_item *si)
{
state_item *dsi = (state_item *) gl_list_get_at (queue, 0);
gl_list_remove_at (queue, 0);
- if (dsi->trans >= 0)
- gl_list_add_last (queue, &state_items[dsi->trans]);
+ if (SI_DISABLED (dsi - state_items))
+ continue;
+
+ if (dsi->trans >= 0 && !SI_DISABLED (dsi->trans))
+ {
+ const state_item *trans = &state_items[dsi->trans];
+ bitset_reset (trans->revs, dsi - state_items);
+ if (bitset_empty_p (trans->revs))
+ gl_list_add_last (queue, trans);
+ }
if (dsi->prods)
{
@@ -407,32 +414,15 @@ prune_forward (const state_item *si)
state_item_number sin;
BITSET_FOR_EACH (biter, dsi->prods, sin, 0)
{
+ if (SI_DISABLED (sin))
+ continue;
const state_item *prod = &state_items[sin];
bitset_reset (prod->revs, dsi - state_items);
if (bitset_empty_p (prod->revs))
gl_list_add_last (queue, prod);
}
}
- if (dsi != si)
- disable_state_item (dsi);
- }
- gl_list_free (queue);
-}
-/* disable all state_item paths that lead to
- * si and nowhere else.
- */
-static void
-prune_backward (const state_item *si)
-{
- state_item_list queue =
- gl_list_create (GL_LINKED_LIST, NULL, NULL, NULL, true, 1,
- (const void **) &si);
-
- while (gl_list_size (queue) > 0)
- {
- state_item *dsi = (state_item *) gl_list_get_at (queue, 0);
- gl_list_remove_at (queue, 0);
bitset_iterator biter;
state_item_number sin;
BITSET_FOR_EACH (biter, dsi->revs, sin, 0)
@@ -440,7 +430,9 @@ prune_backward (const state_item *si)
if (SI_DISABLED (sin))
continue;
state_item *rev = &state_items[sin];
- if (rev->prods)
+ if (&state_items[rev->trans] == dsi)
+ gl_list_add_last (queue, rev);
+ else if (rev->prods)
{
bitset_reset (rev->prods, dsi - state_items);
if (bitset_empty_p (rev->prods))
@@ -449,16 +441,13 @@ prune_backward (const state_item *si)
else
gl_list_add_last (queue, rev);
}
- if (dsi != si)
- disable_state_item (dsi);
+ disable_state_item (dsi);
}
gl_list_free (queue);
}
-/*
- To make searches more efficient, we can prune away paths that are
- caused by disabled transitions.
- */
+/* To make searches more efficient, prune away paths that are caused
+ by disabled transitions. */
static void
prune_disabled_paths (void)
{
@@ -466,11 +455,7 @@ prune_disabled_paths (void)
{
state_item *si = &state_items[i];
if (si->trans == -1 && item_number_is_symbol_number (*si->item))
- {
- prune_forward (si);
- prune_backward (si);
- disable_state_item (si);
- }
+ prune_state_item (si);
}
}