| Message ID | 20210417153627.GA50228@ashish-NUC8i5BEH |
|---|---|
| State | New |
| Headers | show |
| Series | media: atomisp: silence "dubious: !x | !y" warning | expand |
On Sat, Apr 17, 2021 at 08:56:13PM +0200, Mauro Carvalho Chehab wrote: > Em Sat, 17 Apr 2021 21:06:27 +0530 > Ashish Kalra <eashishkalra@gmail.com> 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. > > > > Signed-off-by: Ashish Kalra <eashishkalra@gmail.com> > > --- > > .../media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c > > index 358cb7d2cd4c..3b850bb2d39d 100644 > > --- a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c > > +++ b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c > > @@ -58,7 +58,7 @@ sh_css_vf_downscale_log2( > > unsigned int ds_log2 = 0; > > unsigned int out_width; > > > > - if ((!out_info) | (!vf_info)) > > + if ((!out_info) || (!vf_info)) > > > While here, please get rid of the unneeded parenthesis: > > if (!out_info || !vf_info) > > > > return -EINVAL; > > > > out_width = out_info->res.width; > > > > Thanks, > Mauro Updated Patch as per your feedback Thanks Ashish
On Sat, Apr 17, 2021 at 09:31:32PM +0000, David Laight wrote: > > > 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. They both will have the same value here and any half-decent compiler know that and thus generate the same code, so no worries about efficiency. Sparse complains because the programmer's intention is not clear. Was a boolean context or a bitwise context that was meant? Maybe '||' was meant and the RHS had to be short cut? Maybe what was meant was '~x | ~y'? -- Luc
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@gmail.com> 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. regards, dan carpenter
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@gmail.com> 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)
Hi Ashish, On 18/04/2021 03:26, Ashish Kalra wrote: > On Sat, Apr 17, 2021 at 08:56:13PM +0200, Mauro Carvalho Chehab wrote: >> Em Sat, 17 Apr 2021 21:06:27 +0530 >> Ashish Kalra <eashishkalra@gmail.com> 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. >>> >>> Signed-off-by: Ashish Kalra <eashishkalra@gmail.com> >>> --- >>> .../media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c >>> index 358cb7d2cd4c..3b850bb2d39d 100644 >>> --- a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c >>> +++ b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c >>> @@ -58,7 +58,7 @@ sh_css_vf_downscale_log2( >>> unsigned int ds_log2 = 0; >>> unsigned int out_width; >>> >>> - if ((!out_info) | (!vf_info)) >>> + if ((!out_info) || (!vf_info)) >> >> >> While here, please get rid of the unneeded parenthesis: >> >> if (!out_info || !vf_info) >> >> >>> return -EINVAL; >>> >>> out_width = out_info->res.width; >> >> >> >> Thanks, >> Mauro > Updated Patch as per your feedback Please don't post patches as an attachment. Just post it inline as you did the first time, but with Subject prefix [PATCHv2]. Thanks! Hans
diff --git a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c index 358cb7d2cd4c..3b850bb2d39d 100644 --- a/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c +++ b/drivers/staging/media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c @@ -58,7 +58,7 @@ sh_css_vf_downscale_log2( unsigned int ds_log2 = 0; unsigned int out_width; - if ((!out_info) | (!vf_info)) + if ((!out_info) || (!vf_info)) return -EINVAL; out_width = out_info->res.width;
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. Signed-off-by: Ashish Kalra <eashishkalra@gmail.com> --- .../media/atomisp/pci/isp/kernels/vf/vf_1.0/ia_css_vf.host.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)