[clang] 23058f9 - [OPENMP]Do not use RTTI by default for NVPTX devices.

Wed Jan 15 15:06:24 PST 2020

On Wed, Jan 15, 2020 at 2:52 PM Alexey Bataev <a.bataev at outlook.com> wrote:

> 1. The problem is that it does not produce errors,
>
ATM, it does produce errors when it's disabled.

> it leads to the emission of some declaration that cannot be resolved by
> the linker. This what I was trying to avoid.
>
I'm OK with disabling it on device, but it should be done in a way to keep
RTTI in the host code working.

E.g. this code should compile: https://godbolt.org/z/Gzsrof
It still has your original change, so clang compilation fails. It does not
with NVCC.

2. Yes, I did not disable it on the host side, just for the device side. I
> disabled it only for NVPTX target, which is the device.
>
It's fine to disable it for code generated for the target. However, the
front-end needs to be able to deal with the host-side code where it is OK
to use RTTI.

--Artem

> -------------
> Best regards,
> Alexey Bataev
>
> 15.01.2020 12:49 PM, Artem Belevich пишет:
>
> Thank you.
>
> In general, RTTI should probably be treated similar to how we deal with
> inline assembly and ignore errors if they are in the code that we're not
> going to codegen during this side of compilation. E.g. during host-side
> compilation we don't complain about GPU-side registers in inline assembly
> that x86 target is not aware of.
>
> Disabling RTTI altogether on device side makes it impossible to use in any
> host-side CUDA because RTTI code will be seen by the device-side compiler,
> which will promptly fail, which is exactly what happened in this case --
> host-side template that relied on RTTI failed during device-side
> compilation:
>
>
> https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/arena.h#L536
> google/protobuf/arena.h:536:15: error: use of typeid requires -frtti
>     AllocHook(RTTI_TYPE_ID(T), n);
> ...
> 2 errors generated when compiling for sm_60.
>
> --Artem
>
> On Wed, Jan 15, 2020 at 2:36 PM Alexey Bataev <a.bataev at outlook.com>
> wrote:
>
>> Sure, will revert it ASAP.
>>
>> -------------
>> Best regards,
>> Alexey Bataev
>>
>> 15.01.2020 12:26 PM, Artem Belevich пишет:
>>
>> Alexey,
>>
>> This breaks compilation of our cuda code which happens to transitively
>> include protobuf headers.
>> Can you, please, revert it for now until we figure out how RTTI should be
>> handled?
>>
>> --Artem
>>
>> On Tue, Jan 14, 2020 at 3:15 PM Alexey Bataev via cfe-commits <
>> cfe-commits at lists.llvm.org> wrote:
>>
>>>
>>> Author: Alexey Bataev
>>> Date: 2020-01-14T18:12:06-05:00
>>> New Revision: 23058f9dd4d7e18239fd63b6da52549514b45fda
>>>
>>> URL:
>>> https://github.com/llvm/llvm-project/commit/23058f9dd4d7e18239fd63b6da52549514b45fda
>>> DIFF:
>>> https://github.com/llvm/llvm-project/commit/23058f9dd4d7e18239fd63b6da52549514b45fda.diff
>>>
>>> LOG: [OPENMP]Do not use RTTI by default for NVPTX devices.
>>>
>>> NVPTX does not support RTTI, so disable it by default.
>>>
>>> Added:
>>>     clang/test/Driver/openmp-offload-gpu.cpp
>>>
>>> Modified:
>>>     clang/lib/Driver/ToolChain.cpp
>>>
>>> Removed:
>>>
>>>
>>>
>>>
>>> ################################################################################
>>> diff  --git a/clang/lib/Driver/ToolChain.cpp
>>> b/clang/lib/Driver/ToolChain.cpp
>>> index cab97b1a601a..3ebbd30195b3 100644
>>> --- a/clang/lib/Driver/ToolChain.cpp
>>> +++ b/clang/lib/Driver/ToolChain.cpp
>>> @@ -68,7 +68,8 @@ static ToolChain::RTTIMode CalculateRTTIMode(const
>>> ArgList &Args,
>>>    }
>>>
>>>    // -frtti is default, except for the PS4 CPU.
>>> -  return (Triple.isPS4CPU()) ? ToolChain::RM_Disabled :
>>> ToolChain::RM_Enabled;
>>> +  return (Triple.isPS4CPU() || Triple.isNVPTX()) ?
>>> ToolChain::RM_Disabled
>>> +                                                 :
>>> ToolChain::RM_Enabled;
>>>  }
>>>
>>>  ToolChain::ToolChain(const Driver &D, const llvm::Triple &T,
>>>
>>> diff  --git a/clang/test/Driver/openmp-offload-gpu.cpp
>>> b/clang/test/Driver/openmp-offload-gpu.cpp
>>> new file mode 100644
>>> index 000000000000..9da7308506ae
>>> --- /dev/null
>>> +++ b/clang/test/Driver/openmp-offload-gpu.cpp
>>> @@ -0,0 +1,20 @@
>>> +///
>>> +/// Perform several driver tests for OpenMP offloading
>>> +///
>>> +
>>> +// REQUIRES: clang-driver
>>> +// REQUIRES: x86-registered-target
>>> +// REQUIRES: powerpc-registered-target
>>> +// REQUIRES: nvptx-registered-target
>>> +
>>> +///
>>> ###########################################################################
>>> +
>>> +/// PTXAS is passed -c flag by default when offloading to an NVIDIA
>>> device using OpenMP
>>> +/// Check that the flag is passed when -fopenmp-relocatable-target is
>>> used.
>>> +// RUN:   %clangxx -### -fopenmp=libomp
>>> -fopenmp-targets=nvptx64-nvidia-cuda \
>>> +// RUN:          -save-temps -no-canonical-prefixes %s -x c++ -c 2>&1 \
>>> +// RUN:   | FileCheck -check-prefix=CHK-RTTI %s
>>> +
>>> +// CHK-RTTI: clang{{.*}}" "-triple" "nvptx64-nvidia-cuda"
>>> +// CHK-RTTI-SAME: "-fno-rtti"
>>> +
>>>
>>>
>>>
>>> _______________________________________________
>>> cfe-commits mailing list
>>> cfe-commits at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>>>
>>
>>
>> --
>> --Artem Belevich
>>
>>
>
> --
> --Artem Belevich
>
>

-- 
--Artem Belevich
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