On Fri, Feb 20, 2015 at 04:35:05PM +0100, Marek Polacek wrote: > Note that first version of -Wlogical-not-parentheses didn't warn > when LHS had a boolean type, this has been changed later on. I have > no strong preference either way. > > > As the argument is already folded, it isn't easy to determine > > those cases always, but I hope the following is sufficient until we switch > > to late folding. > > Yes, this means that we warn for > > return !(a != 0) == b; > > but not for > > return !(a == 0) == b; > > I think we can live with that for now.
Well, for the !! case another option is, as we at least in the C++ FE peek at the first token if it is !, peek another token if it is ! too. Then we would warn for !(!a) == b and would not warn for !!a == b. Guess that would be fine too. For the ! of bool, if we want to detect that case (have done that primarily because clang++ does that (clang doesn't support -Wlogical-not-parentheses)), for C because of the conversion to int it is still more likely we catch it, but for C++ we'd need to parse the expression twice or do similar uglities. For everything the answer is of course less folding early, but it will take some time. > The C part is ok. Maybe we should also update the docs to reflect that > -Wlogical-not-parentheses does not warn if the RHS *or LHS* operand is of > a boolean type. Thanks, RHS operand or operand of ! on the LHS to be precise, though that is not what is implemented for C++ right now, e.g. !(a > 20) == 0 shouldn't warn in C++ because a > 20 is bool, but it is really hard after the folding to find out what was the original ! operand. Though of course, it would be weird if we don't warn for !(a > 20) == 0 for C (where a > 20 is not _Bool) but do warn for C++ (where it is bool). If preferred, I can do just the !! case that in theory should be reliably detected, and warn for everything else. Jakub