dfa: retain sequences of similar nodes in optimization

DFA was merging similar nodes when it should not.  For example,
it would convert a+a+a to a+a.  Now, a sequence of similar nodes
is not merged.

Problem reported by Gonzalo Padrino in https://bugs.gnu.org/44351

* lib/dfa.c (merge_nfa_state): Skip the follow for repetition in
optimization.

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/dfa.c b/lib/dfa.c
index 74aafa2ee9..6d880c1331 100644
--- a/lib/dfa.c
+++ b/lib/dfa.c
@@ -2438,7 +2438,7 @@ merge_nfa_state (struct dfa *d, idx_t tindex, char *flags,
           continue;
         }
 
-      if (!(flags[sindex] & (OPT_LPAREN | OPT_RPAREN)))
+      if (sindex != tindex && !(flags[sindex] & (OPT_LPAREN | OPT_RPAREN)))
         {
           idx_t j;
 
@@ -2446,6 +2446,9 @@ merge_nfa_state (struct dfa *d, idx_t tindex, char *flags,
             {
               idx_t dindex = follows[tindex].elems[j].index;
 
+              if (dindex == tindex)
+                continue;
+
               if (follows[tindex].elems[j].constraint != iconstraint)
                 continue;