[PATCH 10/13] s390: Use sqrt{f} builtin

[Szabolcs Nagy]

The 06/10/2020 17:39, Stefan Liebler via Libc-alpha wrote:
> Hi Adhemerval,
> 
> my last tests with the sqrt builtin on s390x showed that gcc emits a
> call to libm which would lead to an infinite loop:
> if (x < 0)
>  sqrt(x)
> else
>  sqdbr-instruction

in general the builtins based implementation
must be compiled with -fno-math-errno if
they have error conditions otherwise math-errno
may cause the compiler not to do a single
instruction inline like in this sqrt case.

> 
> Can you have a look into the generated code?
> I will also apply your series and perform some test-runs. (next week as
> I'll be on vacation the next days)
> 
> Then I'll also have a look at the fma-builtins. But those should be fine
> for float and double.
> 
> Bye.
> Stefan
> 
> On 6/9/20 11:32 PM, Adhemerval Zanella via Libc-alpha wrote:
> > Checked on s390x-linux-gnu.
> > ---
> >  sysdeps/s390/fpu/e_sqrt.c                 | 30 -----------------------
> >  sysdeps/s390/fpu/e_sqrtf.c                | 30 -----------------------
> >  sysdeps/s390/fpu/math-use-builtins-sqrt.h |  4 +++
> >  3 files changed, 4 insertions(+), 60 deletions(-)
> >  delete mode 100644 sysdeps/s390/fpu/e_sqrt.c
> >  delete mode 100644 sysdeps/s390/fpu/e_sqrtf.c
> >  create mode 100644 sysdeps/s390/fpu/math-use-builtins-sqrt.h
> > 
> > diff --git a/sysdeps/s390/fpu/e_sqrt.c b/sysdeps/s390/fpu/e_sqrt.c
> > deleted file mode 100644
> > index 484c6aae95..0000000000
> > --- a/sysdeps/s390/fpu/e_sqrt.c
> > +++ /dev/null
> > @@ -1,30 +0,0 @@
> > -/* Copyright (C) 2004-2020 Free Software Foundation, Inc.
> > -   Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>.
> > -   This file is part of the GNU C Library.
> > -
> > -   The GNU C Library is free software; you can redistribute it and/or
> > -   modify it under the terms of the GNU Lesser General Public
> > -   License as published by the Free Software Foundation; either
> > -   version 2.1 of the License, or (at your option) any later version.
> > -
> > -   The GNU C Library is distributed in the hope that it will be useful,
> > -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > -   Lesser General Public License for more details.
> > -
> > -   You should have received a copy of the GNU Lesser General Public
> > -   License along with the GNU C Library; if not, see
> > -   <https://www.gnu.org/licenses/>.  */
> > -
> > -#include <math_private.h>
> > -#include <libm-alias-finite.h>
> > -
> > -double
> > -__ieee754_sqrt (double x)
> > -{
> > -  double res;
> > -
> > -  __asm__ ( "sqdbr %0,%1" : "=f" (res) : "f" (x) );
> > -  return res;
> > -}
> > -libm_alias_finite (__ieee754_sqrt, __sqrt)
> > diff --git a/sysdeps/s390/fpu/e_sqrtf.c b/sysdeps/s390/fpu/e_sqrtf.c
> > deleted file mode 100644
> > index bce49c90f1..0000000000
> > --- a/sysdeps/s390/fpu/e_sqrtf.c
> > +++ /dev/null
> > @@ -1,30 +0,0 @@
> > -/* Copyright (C) 2004-2020 Free Software Foundation, Inc.
> > -   Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>.
> > -   This file is part of the GNU C Library.
> > -
> > -   The GNU C Library is free software; you can redistribute it and/or
> > -   modify it under the terms of the GNU Lesser General Public
> > -   License as published by the Free Software Foundation; either
> > -   version 2.1 of the License, or (at your option) any later version.
> > -
> > -   The GNU C Library is distributed in the hope that it will be useful,
> > -   but WITHOUT ANY WARRANTY; without even the implied warranty of
> > -   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> > -   Lesser General Public License for more details.
> > -
> > -   You should have received a copy of the GNU Lesser General Public
> > -   License along with the GNU C Library; if not, see
> > -   <https://www.gnu.org/licenses/>.  */
> > -
> > -#include <math_private.h>
> > -#include <libm-alias-finite.h>
> > -
> > -float
> > -__ieee754_sqrtf (float x)
> > -{
> > -  float res;
> > -
> > -  __asm__ ( "sqebr %0,%1" : "=f" (res) : "f" (x) );
> > -  return res;
> > -}
> > -libm_alias_finite (__ieee754_sqrtf, __sqrtf)
> > diff --git a/sysdeps/s390/fpu/math-use-builtins-sqrt.h b/sysdeps/s390/fpu/math-use-builtins-sqrt.h
> > new file mode 100644
> > index 0000000000..e94c915ba6
> > --- /dev/null
> > +++ b/sysdeps/s390/fpu/math-use-builtins-sqrt.h
> > @@ -0,0 +1,4 @@
> > +#define USE_SQRT_BUILTIN 1
> > +#define USE_SQRTF_BUILTIN 1
> > +#define USE_SQRTL_BUILTIN 0
> > +#define USE_SQRTF128_BUILTIN 0
> > 
> 

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