Re: [nvptx] Pass -m32/-m64 to host_compiler if it has multilib support

[Andrew Pinski <pinskia@gmail.com>]

On Thu, Aug 8, 2024 at 6:11 AM Prathamesh Kulkarni
<prathameshk@nvidia.com> wrote:
>
> Hi Richard,
> After differing NUM_POLY_INT_COEFFS fix for AArch64/nvptx offloading, the following minimal test:
>
> int main()
> {
>   int x;
>   #pragma omp target map(x)
>     x = 5;
>   return x;
> }
>
> compiled with -fopenmp -foffload=nvptx-none now fails with:
> gcc: error: unrecognized command-line option '-m64'
> nvptx mkoffload: fatal error: ../install/bin/gcc returned 1 exit status compilation terminated.
>
> As mentioned in RFC email, this happens because nvptx/mkoffload.cc:compile_native passes -m64/-m32 to host compiler depending on whether
> offload_abi is OFFLOAD_ABI_LP64 or OFFLOAD_ABI_ILP32, and aarch64 backend doesn't recognize these options.
>
> Based on your suggestion in: https://gcc.gnu.org/pipermail/gcc/2024-July/244470.html,
> The attached patch generates new macro HOST_MULTILIB derived from $enable_as_accelerator_for, and in mkoffload.cc it gates passing -m32/-m64
> to host_compiler on HOST_MULTILIB. I verified that the macro is set to 0 for aarch64 host (and thus avoids above unrecognized command line option error),
> and is set to 1 for x86_64 host.
>
> Does the patch look OK ?

Note I think the usage of the name MULTILIB here is wrong because
aarch64 (and riscv) could have MUTLILIB support just the options are
different. For aarch64, it would be -mabi=ilp32/-mabi=lp64 (riscv it
is more complex).

This most likely should be something more complex due to the above.
Maybe call it HOST_64_32 but even that seems wrong due to Aarch64
having ILP32 support and such.
What about HOST_64ABI_OPTS="-mabi=lp64"/HOST_32ABI_OPTS="-mabi=ilp32"
but  I am not sure if that would be enough to support RISCV which
requires two options.

Thanks,
Andrew Pinski

>
> Signed-off-by: Prathamesh Kulkarni <prathameshk@nvidia.com>
>
> Thanks,
> Prathamesh