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Message-ID: <20170610213737.GU1627@brightrain.aerifal.cx>
Date: Sat, 10 Jun 2017 17:37:37 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] s390x: Add single instruction math functions
On Sat, Jun 10, 2017 at 04:22:24PM -0400, David Edelsohn wrote:
> On Sat, Jun 10, 2017 at 3:48 PM, Rich Felker <dalias@...c.org> wrote:
> > On Sat, Jun 10, 2017 at 02:53:14PM -0400, David Edelsohn wrote:
> >> On Sat, Jun 10, 2017 at 2:29 PM, Szabolcs Nagy <nsz@...t70.net> wrote:
> >> > * David Edelsohn <dje.gcc@...il.com> [2017-06-10 13:25:00 -0400]:
> >> >> On Sat, Jun 10, 2017 at 11:36 AM, Szabolcs Nagy <nsz@...t70.net> wrote:
> >> >> > * David Edelsohn <dje.gcc@...il.com> [2017-06-09 10:51:25 -0400]:
> >> >> >> The following patch is a start at single instruction math functions
> >> >> >> for s390x architecture to increase performance.
> >> >> >
> >> >> > looks good, i wonder why gcc does not have builtins support for
> >> >> > ceil, floor, nearbyint, round and trunc
> >> >> >
> >> >> > (on aarch64 the builtins expand to single instruction with
> >> >> > -fno-math-errno, but on s390x they remain libc calls
> >> >>
> >> >> Both the functions and builtins are converted to single instructions
> >> >> for me. What architecture level is your GCC assuming?
> >> >>
> >> >
> >> > i think it's the default s390x config
> >> >
> >> > $ s390x-linux-musl-gcc -v
> >> > Using built-in specs.
> >> > COLLECT_GCC=s390x-linux-musl-gcc
> >> > COLLECT_LTO_WRAPPER=/home/nsz/w/mcm/output/bin/../libexec/gcc/s390x-linux-musl/6.3.0/lto-wrapper
> >> > Target: s390x-linux-musl
> >> > Configured with: ../src_toolchain/configure --enable-languages=c,c++ CFLAGS='-g0 -Os' CXXFLAGS='-g0 -Os' LDFLAGS=-s --disable-nls --with-debug-prefix-map=/home/nsz/w/mcm/build-s390x-linux-musl= --enable-languages=c,c++ --disable-libquadmath --disable-libquadmath-support --disable-decimal-float --disable-multilib --disable-libcilkrts --disable-libvtv --disable-libgomp --disable-libitm --disable-werror --target=s390x-linux-musl --prefix= --libdir=/lib --disable-multilib --with-sysroot=/s390x-linux-musl --enable-tls --disable-libmudflap --disable-libsanitizer --disable-gnu-indirect-function --disable-libmpx --enable-libstdcxx-time --with-build-sysroot=/home/nsz/w/mcm/build-s390x-linux-musl/obj_sysroot
> >> > Thread model: posix
> >> > gcc version 6.3.0 (GCC)
> >> > $ cat a.c
> >> > double f(double x)
> >> > {
> >> > return __builtin_ceil(x);
> >> > }
> >> > $ s390x-linux-musl-gcc -O3 -fno-math-errno -S a.c -o -
> >> > .machinemode zarch
> >> > .machine "z900"
> >>
> >> Note the default architecture is z900 from 2005-2006. The FP
> >> instructions were added with the z196 processors in 2010.
> >
> > In that case the patch should probably have the code inside something
> > like:
> >
> > #ifdef __Z196__ // or whatever the predef macro for the ISA level is
> > // your code here
> > #else
> > #include "../foo.c"
> > #else
> >
> > See src/math/arm/sqrt.c for a similar example.
> >
> >> s390x-linux-musl probably should default to a much newer processor
> >> level, such as at least z196 or zEC12
> >
> > musl's policy is to just follow whatever ISA level the compiler is
> > configured for; you can set this at musl build time with CFLAGS or use
> > a default built into the toolchain at toolchain build time
> > (--with-arch, I think).
>
> Musl already defaults to the later ISA in the rest of the s390x port.
If that's the case it's not a regression and probably okay; someone
can add support for earlier ISA levels as a separate patch if anyone
cares about support for them.
Can you point out in a reply where we already assume later ISA level,
so that someone reading this thread later has it documented?
Rich
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