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

[Jan Vesely]

On Fri, 2015-02-06 at 19:46 +0000, Jose Fonseca wrote:
> I haven't tried this sort of code with MSVC 2013 U4, but at least in the 
> past, MSVC 2013 was refusing certain kinds of variable length arrays.
> 
> And Jan's patch is a stepping stone to -Wvla option  when compiling 
> (option which apply to the whole tree, including parts that are not 
> built with MSVC), in order to preemptively spot uses of VLA in places 
> where MSVC would break.
> 
> So let me do the following: I'll see if MSVC 2013 accepts or refuses the 
> VLA code that caused problems the first time, and then we'll take it 
> from there.

thank you. getting rid of -Wvla entirely would be preferable.

Dylan, I have attached a follow up patch that I planned to post after
these get in. I probably should have included it in the original series
to avoid the confusion.

jan

> 
> Jose
> 
> 
> On 06/02/15 19:19, Dylan Baker wrote:
> > Is this actually necessary? I though that we required MSVC 2013 u4,
> > because it has c99 support.
> >
> > Also, dma_buf tests require libdrm_intel, which doesn't exist/work on
> > windows, so I don't think anyone will be building them with msvc anytime
> > soon.
> >
> > Dylan
> >
> > On Fri, Feb 06, 2015 at 11:49:08AM -0500, Jan Vesely wrote:
> >> 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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> 

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