Re: [PATCH] s390x: Add single instruction math functions

[David Edelsohn <dje.gcc@gmail.com>]

On Sat, Jun 10, 2017 at 2:29 PM, Szabolcs Nagy <nsz@port70.net> wrote:
> * David Edelsohn <dje.gcc@gmail.com> [2017-06-10 13:25:00 -0400]:
>> On Sat, Jun 10, 2017 at 11:36 AM, Szabolcs Nagy <nsz@port70.net> wrote:
>> > * David Edelsohn <dje.gcc@gmail.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.

s390x-linux-musl probably should default to a much newer processor
level, such as at least z196 or zEC12

- David