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From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
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Date: Tue, 15 Jan 2019 14:46:50 +0000
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Subject: Re: [Qemu-devel] [PATCH] include/fpu/softfloat: Fix compilation
 with Clang on s390x
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Richard Henderson <rth@twiddle.net>, Thomas Huth <thuth@redhat.com>, Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= <philmd@redhat.com>, Aurelien Jarno <aurelien@aurel32.net>, Cornelia Huck <cohuck@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, qemu-s390x <qemu-s390x@nongnu.org>


Peter Maydell <peter.maydell@linaro.org> writes:

> On Mon, 14 Jan 2019 at 22:48, Alex Benn=C3=A9e <alex.bennee@linaro.org> w=
rote:
>>
>>
>> Richard Henderson <rth@twiddle.net> writes:
>> > But perhaps
>> >
>> >     unsigned __int128 n =3D (unsigned __int128)n1 << 64 | n0;
>> >     *r =3D n % d;
>> >     return n / d;
>> >
>> > will allow the compiler to do what the assembly does for some 64-bit
>> > hosts.
>>
>> I wonder how much cost is incurred by the jumping to the (libgcc?) div
>> helper? Anyone got an s390x about so we can benchmark the two
>> approaches?
>
> The project has an s390x system available; however it's usually
> running merge build tests so not so useful for benchmarking.
> (I can set up accounts on it but that requires me to faff about
> figuring out how to create new accounts :-))

I'm happy to leave this up to those who care about s390x host
performance (Thomas, Cornelia?). I'm just keen to avoid the divide
helper getting too #ifdefy.

I'll include a CONFIG_INT128 patch in my next patch queue review once
I've double checked and tested under linux-user ;-)

--
Alex Benn=C3=A9e