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

[Jan Vesely]

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.

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.

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

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