[Mesa-dev] [RFC] travis: lower SWR requirement to GCC 4.8, aka std=c++11

[Emil Velikov]

On 5 July 2017 at 19:28, Rowley, Timothy O <timothy.o.rowley at intel.com> wrote:
>
>> On Jul 4, 2017, at 12:01 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>>
>> From: Emil Velikov <emil.velikov at collabora.com>
>>
>> With ealier commit we relaxed the requirement from C++14 to C++11.
>> Update the build script so that it
>>
>> Cc: Tim Rowley <timothy.o.rowley at intel.com
>> Fixes: 0b80b025021 ("swr: relax c++ requirement from c++14 to c++11")
>> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
>> ---
>> Tim, this does _not_ quite work, hence I'm sending it as RFC.
>> The current build failures can be seen here
>>
>> Autotools
>> https://travis-ci.org/evelikov/Mesa/jobs/250043586
>> Scons
>> https://travis-ci.org/evelikov/Mesa/jobs/250043595
>>
>
> gcc-4.8 is throwing up some issues; I’ve patched them in the submission I just made to mesa-stable (swr: modifications to allow gcc-4.8 compilation).  Still get a weird link problem (undefined reference to llvm::RTDyldMemoryManager::getSymbolAddressInProcess), but that looks to be more of a core gallium problem.
>
Can we have the GCC 4.8 fix in master first? On the linking issue - I
recall similar one, and updating LLVM solved it.
Let me see if I can dig up some details.

>> Although I expect additional issues, since w/o the patch a local build
>> throws the following:
>>
>> src/gallium/drivers/swr/rasterizer/core/api.cpp: In function ‘void* SwrCreateContext(SWR_CREATECONTEXT_INFO*)’:
>> src/gallium/drivers/swr/rasterizer/core/api.cpp:111:64: warning: ‘new’ of type ‘SWR_STATS’ with extended alignment 64 [-Waligned-new=]
>>     pContext->pStats = new SWR_STATS[pContext->NumWorkerThreads];
>>                                                                ^
>> src/gallium/drivers/swr/rasterizer/core/api.cpp:111:64: note: uses ‘void* operator new [](std::size_t)’, which does not have an alignment parameter
>> src/gallium/drivers/swr/rasterizer/core/api.cpp:111:64: note: use ‘-faligned-new’ to enable C++17 over-aligned new support
>>
>> src/gallium/drivers/swr/rasterizer/core/threads.cpp: In function ‘void CreateThreadPool(SWR_CONTEXT*, THREAD_POOL*)’:
>> src/gallium/drivers/swr/rasterizer/core/threads.cpp:989:72: warning: ‘new’ of type ‘SWR_STATS’ with extended alignment 64 [-Waligned-new=]
>>         pContext->dcRing[dc].dynState.pStats = new SWR_STATS[numThreads];
>>                                                                        ^
>> src/gallium/drivers/swr/rasterizer/core/threads.cpp:989:72: note: uses ‘void* operator new [](std::size_t)’, which does not have an alignment parameter
>> src/gallium/drivers/swr/rasterizer/core/threads.cpp:989:72: note: use ‘-faligned-new’ to enable C++17 over-aligned new support
>
> These are curious - I’m not seeing warnings like this on gcc-4.8.5.
>
Using gcc (GCC) 7.1.1 20170528, but I've seen it with earlier GCC 7 versions.

Checking SWR_STATS and expanding all the macros gives us:

struct __attribute__((aligned(64))) SWR_STATS
{
    uint64_t DepthPassCount;

    uint64_t PsInvocations;
    uint64_t CsInvocations;
};

... which strictly speaking one does not even need the aligned bits.
Dropping the ALIGN bits may lead to breakage later on.
Which one should be able to catch at compile time via a combination of
static_assert and sizeof/offsetof.

Thanks
Emil