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

[Jose Fonseca]

On 09/02/15 21:29, Jan Vesely wrote:
> On Mon, 2015-02-09 at 19:49 +0000, Jose Fonseca wrote:
>> On 09/02/15 19:17, Ian Romanick wrote:
>>> On 02/06/2015 11:46 AM, 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.
>>>
>>> In Mesa, we can change compiler options in subdirectories.  Is it
>>> possible to do this with cmake?  Like, could we remove -Wvla in
>>> directories that are only built on Linux?  It seems like that could give
>>> us the best of both worlds...
>>
>> Yes, I just confirmed that MSVC 2013 U4 still fails to compile VLA code
>> and was about to propose something similar.
>>
>> In theory this
>>
>>     string (REPLACE "-Wvla" "" CMAKE_C_FLAGS ${CMAKE_C_FLAGS})
>>
>> should undo.  And it does work.  But there's a minor snafu:  this line
>> must be put in the tests/spec/foo/CMakeLists.txt -- if it's put in the
>> tests/spec/foo/CMakeLists.gl*.txt it has no effect --  CMAKE_C_FLAGS is
>> changed, but the source files are still build with -Wvla.
>>
>> (I'm always amazed that the  CMakeLists.txt -> CMakeLists.gl*.txt system
>> works!)
>
> I think it's a good idea to keep the warnings/errors global for the sake
> of consistency. The current setup (-Wvla, -Wdeclaration-after-statement)
> only affects the parts changed in these two patches.

There are pro/cons both ways.  I'm happy to let the people that most 
develop on the affected directories to decide based on their preferences.


Unfortunately it's not possible to tweak CMAKE_C_FLAGS on a per API 
basis as I explained before.  It has to be the whole directory.


> The errors reported below are not caught by -Wvla, since they are not
> variable length arrays. I don't think there's a gcc warning to catch
> those.

Note the errors I pasted were with 
http://cgit.freedesktop.org/piglit/commit/?id=0784e54b75918b94ac974197b736c53ccba69ff1 
reverted.  This is was newest VLA related MSVC build breakage I could find.


Jose

>
> jan
>
>>
>>
>>>> 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
>>>
>>
>> For the record these were MSVC errors:
>>
>> AILED: C:\PROGRA~2\MICROS~4.0\VC\bin\cl.exe   /nologo /DWIN32 /D_WINDOWS
>> /W3 /D_DEBUG /MDd /Zi /Ob0 /Od /RTC1 -I..\..\src
>> -IH:\msvc32\freeglut\include -Itests\util -I..\..\tests\util
>> -IH:\noarch\glext    -W3 -wd4018 -wd4244 -wd4305 -wd4800 /showIncludes
>> -DGLAPIENTRY=__stdcall -DNOMINMAX -DPIGLIT_USE_GLUT
>> -DPIGLIT_USE_GLUT_INIT_ERROR_FUNC -DPIGLIT_USE_OPENGL
>> -DWIN32_LEAN_AND_MEAN=1 -D_CRT_NONSTDC_NO_WARNINGS
>> -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_GNU_SOURCE
>> -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_USE_MATH_DEFINES
>> /Fotarget_api\gl\tests\spec\gl-1.0\CMakeFiles\gl-1.0-readpixsanity.dir\readpix.c.obj
>> /Fdtarget_api\gl\tests\spec\gl-1.0\CMakeFiles\gl-1.0-readpixsanity.dir/
>> /FS -c ..\..\tests\spec\gl-1.0\readpix.c
>> ..\..\tests\spec\gl-1.0\readpix.c(103) : error C2057: expected constant
>> expression
>> ..\..\tests\spec\gl-1.0\readpix.c(103) : error C2466: cannot allocate an
>> array of constant size 0
>> ..\..\tests\spec\gl-1.0\readpix.c(103) : error C2087: 'buf' : missing
>> subscript
>> ..\..\tests\spec\gl-1.0\readpix.c(103) : error C2133: 'buf' : unknown size
>> ..\..\tests\spec\gl-1.0\readpix.c(200) : error C2057: expected constant
>> expression
>> ..\..\tests\spec\gl-1.0\readpix.c(200) : error C2466: cannot allocate an
>> array of constant size 0
>> ..\..\tests\spec\gl-1.0\readpix.c(200) : error C2087: 'buf' : missing
>> subscript
>> ..\..\tests\spec\gl-1.0\readpix.c(200) : error C2133: 'buf' : unknown size
>> ..\..\tests\spec\gl-1.0\readpix.c(281) : error C2057: expected constant
>> expression
>> ..\..\tests\spec\gl-1.0\readpix.c(281) : error C2466: cannot allocate an
>> array of constant size 0
>> ..\..\tests\spec\gl-1.0\readpix.c(281) : error C2087: 'buf' : missing
>> subscript
>> ..\..\tests\spec\gl-1.0\readpix.c(281) : error C2133: 'buf' : unknown size
>>
>>
>> So there's no doubt here: by expecting a constant expression it is clear
>> that MSVC does not support VLA at all.
>>
>>
>> Jose
>