Re: [C/C++ PATCH] -Wlogical-not-parentheses tweaks (PR c/65120)
On Fri, Feb 20, 2015 at 01:03:26AM +0100, Jakub Jelinek wrote: > Hi! > > As reported, !!x == y is quite common in the Linux kernel > and unlike the !x == y case it usually doesn't mean mistyped > !(x == y) or x != y. clang++ apparently doesn't warn about that > either, and it doesn't warn even about the case where ! is applied > to a bool. 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. > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk? > > 2015-02-19 Jakub Jelinek > > PR c/65120 > * c-typeck.c (parser_build_binary_op): Don't warn for > !!x == y or !b == y where b is _Bool. > > * parser.c (cp_parser_binary_expression): Don't warn for > !!x == y or !b == y where b is bool. > > * c-c++-common/pr49706.c: Adjust tests for not warning > about !!x == y or !b == y where b is boolean, and add > some further tests. > * c-c++-common/pr62199-2.c: Likewise. 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, Marek
Re: [C/C++ PATCH] -Wlogical-not-parentheses tweaks (PR c/65120)
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
Re: [C/C++ PATCH] -Wlogical-not-parentheses tweaks (PR c/65120)
On 02/19/2015 07:03 PM, Jakub Jelinek wrote: + /* Avoid warning for !!b == y where b is boolean. */ + && (!DECL_P (current.lhs) + || TREE_TYPE (current.lhs) == NULL_TREE + || TREE_CODE (TREE_TYPE (current.lhs)) != BOOLEAN_TYPE)) There's something wrong here. If the type is null, trying to check its TREE_CODE will SEGV. Jason
Re: [C/C++ PATCH] -Wlogical-not-parentheses tweaks (PR c/65120)
On Fri, Feb 27, 2015 at 05:29:47PM -0500, Jason Merrill wrote: > On 02/19/2015 07:03 PM, Jakub Jelinek wrote: > >+ /* Avoid warning for !!b == y where b is boolean. */ > >+ && (!DECL_P (current.lhs) > >+ || TREE_TYPE (current.lhs) == NULL_TREE > >+ || TREE_CODE (TREE_TYPE (current.lhs)) != BOOLEAN_TYPE)) > > There's something wrong here. If the type is null, trying to check its > TREE_CODE will SEGV. If the type is NULL, then it will just call warn_logical_not_parentheses and won't check TREE_CODE. Only when it is non-NULL, it will check TREE_CODE and if it is not BOOLEAN_TYPE, will call warn_logical_not_parentheses. Jakub
Re: [C/C++ PATCH] -Wlogical-not-parentheses tweaks (PR c/65120)
On 03/09/2015 10:34 AM, Jakub Jelinek wrote: On Fri, Feb 27, 2015 at 05:29:47PM -0500, Jason Merrill wrote: On 02/19/2015 07:03 PM, Jakub Jelinek wrote: + /* Avoid warning for !!b == y where b is boolean. */ + && (!DECL_P (current.lhs) + || TREE_TYPE (current.lhs) == NULL_TREE + || TREE_CODE (TREE_TYPE (current.lhs)) != BOOLEAN_TYPE)) There's something wrong here. If the type is null, trying to check its TREE_CODE will SEGV. If the type is NULL, then it will just call warn_logical_not_parentheses and won't check TREE_CODE. Only when it is non-NULL, it will check TREE_CODE and if it is not BOOLEAN_TYPE, will call warn_logical_not_parentheses. You're right, of course. I guess I was reading the || as an &&. The patch is OK. Jason
