[Piglit] [PATCH 2/3] Use alloca instead of variable length arrays

[Jan Vesely]

ping

On Fri, 2014-12-12 at 19:13 -0500, Jan Vesely wrote:
> On Fri, 2014-12-12 at 14:49 -0800, Matt Turner wrote:
> > On Fri, Dec 12, 2014 at 2:13 PM, Jan Vesely <jan.vesely at rutgers.edu> wrote:
> > > On Fri, 2014-12-12 at 13:37 -0800, Matt Turner wrote:
> > >> On Fri, Dec 12, 2014 at 1:23 PM, Jan Vesely <jan.vesely at rutgers.edu> wrote:
> > >> > On Fri, 2014-12-12 at 12:58 -0800, Matt Turner wrote:
> > >> >> I'm curious what the motivation for removing variably-sized arrays is,
> > >> >> but if I accept that that's a good thing to do then the first patch
> > >> >> makes sense, but I don't understand this one.
> > >> >>
> > >> >> How is a variably-size array different from using alloca()?
> > >> >
> > >> > variable size arrays are a c99 feature not supported by msvc (that's why
> > >> > there is a warning). I don't know which parts actually do need to build
> > >> > using msvc, but it seemed like a good idea to reduce warning output (and
> > >> > improve consistency with code that needs to build using msvc).
> > >> >
> > >> > In the first patch I used alloca+free, because it looked nicer than
> > >> > doing size arithmetic. The other cases allocate byte arrays, and the
> > >> > only difference is that alloca (_alloca) is supported by msvc.
> > >>
> > >> Okay, then this patch doesn't do anything useful, since these tests
> > >> shouldn't be built with MSVC. dma_bufs are a Linux thing.
> > >
> > > yes, I understand that, the point was not to build them using msvc.
> > >
> > > the patch usefulness is in enabling switch Wvla to error instead of
> > > warning. other than that, it just reduces warning output.
> > 
> > Ah, I see. Okay.
> > 
> > For my own curiosity, does this actually change the compiled code?
> 
> Looks like the vla version uses fewer instructions but the code size is
> the same (for -O3).
> I'm using gcc 4.9.2 that comes with F21
> 
> I have attached release and debug versions of
> ext_image_dma_buf_import-ownership_transfer piglit_display()
> if you're interested
> 
> jan
> 
> 

-- 
Jan Vesely <jan.vesely at rutgers.edu>
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