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

[Szabolcs Nagy <nsz@port70.net>]

* David Edelsohn <dje.gcc@gmail.com> [2017-06-12 09:54:54 -0400]:
> On Mon, Jun 12, 2017 at 9:28 AM, David Edelsohn <dje.gcc@gmail.com> wrote:
> > On Mon, Jun 12, 2017 at 5:03 AM, Szabolcs Nagy <nsz@port70.net> wrote:
> >> * David Edelsohn <dje.gcc@gmail.com> [2017-06-11 22:46:09 -0400]:
> >>> The following IBM table of supported and tested systems
> >>>
> >>> https://www-03.ibm.com/systems/z/os/linux/resources/testedplatforms.html
> >>>
> >>> shows that RHEL 7 and SLES 12 require at least z196, and Ubuntu 16.04
> >>> requires at least zEC12.
> >>>
> >>> I can't find any official hardware requirements description for Alpine
> >>> Linux. I tend to doubt that user would run it on older hardware,
> >>> especially hardware no longer supported by other, modern Linux
> >>> distributions.
> >>>
> >>> Building musl libc on older hardware is a nice accomplishment, but
> >>> investing effort and complexity to maintain support probably isn't
> >>> useful to any musl libc user and probably isn't a productive use of
> >>> developer resources.
> >>>
> >>> I will continue to inquire if there is a simple technique to accomplish this.
> >
> > Apparently GCC 7.1 added architecture macros.
> >
> > As Tuan referenced, Alpine Linux also requires z196 as the minimum
> > architecture level.  I believe that it would be better for s390-musl
> > to default to z196 ISA than musl to require GCC 7.1.
> 
> Would a patch such as the following be acceptable?
> 
> Thanks, David
> 
> diff --git a/configure b/configure
> index c2db298..a9e0256 100755
> --- a/configure
> +++ b/configure
> @@ -494,6 +494,15 @@ fnmatch '-mtune=*|*\ -mtune=*' "$CC $CFLAGS" || tryldflag C
>  fi
> 
>  #
> +# On s390x, default to z196 architecture and zEC12 tuning to support newer math
> +# instructions.
> +#
> +if test "$ARCH" = "s390x" ; then
> +fnmatch '-march=*|*\ -march=*' "$CC $CFLAGS" || tryldflag CFLAGS_AUTO
> -march=z196
> +fnmatch '-mtune=*|*\ -mtune=*' "$CC $CFLAGS" || tryldflag CFLAGS_AUTO
> -mtune=zEC12
> +fi
> +
> +#
>  # Even with -std=c99, gcc accepts some constructs which are constraint
>  # violations. We want to treat these as errors regardless of whether
>  # other purely stylistic warnings are enabled -- especially implicit

well the toolchain may be configured for a different/newer cpu
and then we may not want to override that.. what about

diff --git a/configure b/configure
index c2db298c..bcaf3a7d 100755
--- a/configure
+++ b/configure
@@ -656,6 +656,12 @@ trycppif __LITTLE_ENDIAN__ "$t" && SUBARCH=${SUBARCH}le
 trycppif _SOFT_FLOAT "$t" && fail "$0: error: soft-float not supported on powerpc64"
 fi
 
+if test "$ARCH" = "s390x" ; then
+echo 'float x; void f(){__asm__("fiebra %0,6,%1,4":"=f"(x):"f"(x));}' > "$tmpc"
+$CC $CFLAGS_C99FSE $CPPFLAGS $CFLAGS -c -o /dev/null "$tmpc" >/dev/null 2>&1 ||
+  fail "$0: error: s390x isa level is too low, use at least -march=z196"
+fi
+
 if test "$ARCH" = "sh" ; then
 tryflag CFLAGS_AUTO -Wa,--isa=any
 trycppif __BIG_ENDIAN__ "$t" && SUBARCH=${SUBARCH}eb