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Re: [Qemu-devel] [PATCH] include/fpu/softfloat: Fix compilation with Cla

From: Alex Bennée
Subject: Re: [Qemu-devel] [PATCH] include/fpu/softfloat: Fix compilation with Clang on s390x
Date: Tue, 15 Jan 2019 14:46:50 +0000
User-agent: mu4e 1.1.0; emacs 26.1.91

Peter Maydell <address@hidden> writes:

> On Mon, 14 Jan 2019 at 22:48, Alex Bennée <address@hidden> wrote:
>> Richard Henderson <address@hidden> writes:
>> > But perhaps
>> >
>> >     unsigned __int128 n = (unsigned __int128)n1 << 64 | n0;
>> >     *r = 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 Bennée

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