Am Donnerstag, dem 05.12.2024 um 22:14 -0800 schrieb Linus Torvalds: > On Thu, 5 Dec 2024 at 18:26, David Laight <David.Laight@xxxxxxxxxx> wrote: > > > > From: Vincent Mailhol > > > ACK. Would adding a suggested--by Linus tag solve your concern? > > I'm genberally the one person who doesn't need any more credit ;) > > > I actually suspect the first patches to change __is_constexpr() to > > use _Generic were from myself. > > Yes. And David was also I think the one who suggested something else > than "!!" originally too. > > I may have liked "!!" for being very idiomatic and traditional C, but > there were those pesky compilers that warn about "integer in bool > context" or whatever the annoying warning was when then doing the > "multiply by zero" to turn a constant expression into a constant zero > expression. > > So that > > #define is_const(x) __is_const_zero(0 * (x)) > > causes issues when 'x' is not an integer expression (think > "is_const(NULL)" or "is_const(1 == 2)". > > Side note: I think "(x) == 0" will make sparse unhappy when 'x' is a > pointer, because it results that horrid "use integer zero as NULL > without a cast" thing when the plain zero gets implicitly cast to a > pointer. Which is a really nasty and broken C pattern and should never > have been silent. BTW: I added '-Wzero-as-null-pointer-constant' to GCC 15. Hopefully we can also remove / deprecate this for C2Y. Martin > > I think David suggested using ((x)?0:0) at some point. Silly > nonsensical and complex expression, but maybe that finally gets rid of > all the warnings: > > #define is_const(x) __is_const_zero((x)?0:0) > > might work regardless of the type of 'x'. > > Or does that trigger some odd case too?
