I have a grammar which was working (I thought) for bison
2.3. Or, at least it is in production use, and has no bison
errors :).
When I compile this grammar with bison 2.4.2, I get the
following:
Rules useless in parser due to conflicts
560 senitemEdge: "posedge" expr "iff" expr
562 | "negedge" expr "iff" expr
564 | "edge" expr "iff" expr
The grammar is 200KB, and shrinking it seems to make it work
(sorry), so to reproduce this:
wget http://www.veripool.org/ftp/VParseBison_pretmp.y
bison --version
bison (GNU Bison) 2.4.2
bison -t -d -k -v --report=itemset --report=lookahead \
-p VParseBison -b VParseBison_pretmp \
-o VParseBison_pretmp.c VParseBison_pretmp.y
In 2.4.2 the conflict seems to be against the rules
1060 ev_expr: senitemEdge
1061 | ev_expr "iff" expr
However that doesn't make sense to me because while ev_expr
has most of the rules present in expr, expr doesn't include
the rules in ev_expr. Thus once "posedge" is parsed I'd
expect the "iff" term should only be found under the
senitemEdge rule, or other rules that shouldn't match
either.
Comparing the .output files between versions, it looks like
2.3 has states 3404-3406, and 4015-4017, which are not
present in 2.4.2. These states indeed are implement part of
expr, which indeed include the "iff" term.
Of course, it's possible that there was an error in the
original grammar that the new version now uncovers, but it
escapes me what it would be.
Thanks
