From: Dan Carpenter > Sent: 20 April 2021 11:28 > > On Sat, Apr 17, 2021 at 09:31:32PM +0000, David Laight wrote: > > From: Mauro Carvalho Chehab > > > Sent: 17 April 2021 19:56 > > > > > > Em Sat, 17 Apr 2021 21:06:27 +0530 > > > Ashish Kalra <eashishkalra@xxxxxxxxx> escreveu: > > > > > > > Upon running sparse, "warning: dubious: !x | !y" is brought to notice > > > > for this file. Logical and bitwise OR are basically the same in this > > > > context so it doesn't cause a runtime bug. But let's change it to > > > > logical OR to make it cleaner and silence the Sparse warning. > > > > The old code is very likely to by slightly more efficient. > > > > It may not matter here, but it might in a really hot path. > > > > Since !x | !y and !x || !y always have the same value > > why is sparse complaining at all. > > > > Smatch doesn't warn about | vs || if both sides are true/false. But > I've occasionally asked people if they were trying to do a fast path > optimization but it's always just a typo. The problem is with people blindly patching code to 'fix' these warnings. It might just be a fast path optimisation - which they break. Trying to beat the compiler into submission can be hard though. Getting it to 'or' together the outputs from a series of x86 'setne' instructions isn't for the faint hearted. Not helped by the instruction only setting %al. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
