ielr: fix crash on memory management

Reported by Dwight Guth.
https://lists.gnu.org/r/bug-bison/2020-06/msg00037.html

* src/AnnotationList.c (AnnotationList__computePredecessorAnnotations):
Beware that SBITSET__FOR_EACH nests _two_ for-loops, so "break" does
not actually break out of it.
That was the only occurrence in the code.
* src/Sbitset.h (SBITSET__FOR_EACH): Warn passersby.

NEWS

@@ -44,6 +44,10 @@ GNU Bison NEWS
   string aliases semantically equivalent but syntactically different (e.g.,
   "A", "\x41", "\101") are considered to be different.
 
+*** Crash when generating IELR
+
+  An old, well hidden, bug in the generation of IELR parsers was fixed.
+
 ** New features
 
 *** File prefix mapping

THANKS

@@ -59,6 +59,7 @@ Di-an Jan                 [email protected]
 Dick Streefland           [email protected]
 Didier Godefroy           [email protected]
 Don Macpherson            [email protected]
+Dwight Guth               [email protected]
 Efi Fogel                 [email protected]
 Enrico Scholz             [email protected]
 Eric Blake                [email protected]

src/AnnotationList.c

@@ -276,7 +276,8 @@ AnnotationList__computePredecessorAnnotations (
                         obstack_free (annotations_obstackp,
                                       annotation_node->contributions[ci]);
                         annotation_node->contributions[ci] = NULL;
-                        break;
+                        // "Break" out of SBITSET__FOR_EACH.
+                        goto after_sbitset__for_each;
                       }
                     else
                       {
@@ -309,6 +310,7 @@ AnnotationList__computePredecessorAnnotations (
                                     predecessor_item);
                   }
               }
+          after_sbitset__for_each:;
           }
           if (annotation_node->contributions[ci])
             {

src/Sbitset.h

@@ -81,6 +81,8 @@ void Sbitset__fprint (Sbitset self, Sbitset__Index nbits, FILE *file);
       *ptr_self = *ptr_other1 | *ptr_other2;                            \
   } while (0)
 
+/* ATTENTION: there are *two* loops here, "break" and "continue" will
+   not apply to the whole loop, just the inner one.  */
 # define SBITSET__FOR_EACH(SELF, NBITS, ITER, INDEX)                    \
   for ((ITER) = (SELF); (ITER) < (SELF) + Sbitset__nbytes (NBITS); ++(ITER)) \
     if (*(ITER) != 0)                                                   \