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

[Jose Fonseca]

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.

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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