On Thu, Jun 29, 2023 at 12:10 PM Krister Walfridsson via Gcc <gcc@gcc.gnu.org> wrote: > > On Thu, 29 Jun 2023, Richard Biener wrote: > > > IIRC we have some simplification rules that turn bit operations into > > arithmetics. Arithmetic is allowed if it keeps the values inside > > [-1,0] for signed bools or [0, 1] for unsigned bools. > > > >> I have now verified that all cases seems to be just one operation of this > >> form (where _127 has the value 0 or 1), so it cannot construct values > >> such as 42. But the wide signed Boolean can have the three different > >> values 1, 0, and -1, which I still think is at least one too many. :) > > > > Yeah, I'd be interested in a testcase that shows this behavior. > > I created PR 110487 with one example. > > > >> I'll update my tool to complain if the value is outside the range [-1, 1]. > > It is likely that all issues I have seen so far are due to PR 110487, so > I'll keep the current behavior that complains if the value is outside the > range [-1, 0].
Yes there are many similar to this all over GCC's folding. In this case checking TYPE_PRECISION as described in the match.pd is not even the right approach. The whole TYPE_PRECISION on boolean types is definitely a big can of worms. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102622 is related but that was signed boolean:1. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106053 is another related case. For this weekend, I am going to audit some of the match patterns for these issues. > > /Krister
