x86: Add a new option -mdaz-ftz to enable FTZ and DAZ flags in MXCSR.

> The quoted patch shows -shared in context and  you didn't post a
> backport version
> to look at.  But yes, we shouldn't change -shared behavior on a
> branch, even less so make it
> inconsistent between targets.
Here's the patch.

Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
Ok for GCC 11/12 backport?

    if (mdaz-ftz)
      link crtfastmath.o
    else if ((Ofast || ffast-math || funsafe-math-optimizations)
             && !mno-daz-ftz)
      link crtfastmath.o
    else
      Don't link crtfastmath.o

gcc/ChangeLog:

	* config/i386/cygwin.h (ENDFILE_SPEC): Link crtfastmath.o
	whenever -mdaz-ftz is specified. Don't link crtfastmath.o
	when -mno-daz-ftz is specified.
	* config/i386/darwin.h (ENDFILE_SPEC): Ditto.
	* config/i386/gnu-user-common.h
	(GNU_USER_TARGET_MATHFILE_SPEC): Ditto.
	* config/i386/mingw32.h (ENDFILE_SPEC): Ditto.
	* config/i386/i386.opt (mdaz-ftz): New option.
	* doc/invoke.texi (x86 options): Document mftz-daz.
---
 gcc/config/i386/cygwin.h          |  2 +-
 gcc/config/i386/darwin.h          |  4 ++--
 gcc/config/i386/gnu-user-common.h |  2 +-
 gcc/config/i386/i386.opt          |  4 ++++
 gcc/config/i386/mingw32.h         |  2 +-
 gcc/doc/invoke.texi               | 11 ++++++++++-
 6 files changed, 19 insertions(+), 6 deletions(-)

On Wed, May 10, 2023 at 5:10 PM liuhongt <hongtao.liu@intel.com> wrote:
>
> > The quoted patch shows -shared in context and  you didn't post a
> > backport version
> > to look at.  But yes, we shouldn't change -shared behavior on a
> > branch, even less so make it
> > inconsistent between targets.
> Here's the patch.
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> Ok for GCC 11/12 backport?
I'm going to push the patch next week if there's no objection.
>
>     if (mdaz-ftz)
>       link crtfastmath.o
>     else if ((Ofast || ffast-math || funsafe-math-optimizations)
>              && !mno-daz-ftz)
>       link crtfastmath.o
>     else
>       Don't link crtfastmath.o
>
> gcc/ChangeLog:
>
>         * config/i386/cygwin.h (ENDFILE_SPEC): Link crtfastmath.o
>         whenever -mdaz-ftz is specified. Don't link crtfastmath.o
>         when -mno-daz-ftz is specified.
>         * config/i386/darwin.h (ENDFILE_SPEC): Ditto.
>         * config/i386/gnu-user-common.h
>         (GNU_USER_TARGET_MATHFILE_SPEC): Ditto.
>         * config/i386/mingw32.h (ENDFILE_SPEC): Ditto.
>         * config/i386/i386.opt (mdaz-ftz): New option.
>         * doc/invoke.texi (x86 options): Document mftz-daz.
> ---
>  gcc/config/i386/cygwin.h          |  2 +-
>  gcc/config/i386/darwin.h          |  4 ++--
>  gcc/config/i386/gnu-user-common.h |  2 +-
>  gcc/config/i386/i386.opt          |  4 ++++
>  gcc/config/i386/mingw32.h         |  2 +-
>  gcc/doc/invoke.texi               | 11 ++++++++++-
>  6 files changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/gcc/config/i386/cygwin.h b/gcc/config/i386/cygwin.h
> index d06eda369cf..5412c5d4479 100644
> --- a/gcc/config/i386/cygwin.h
> +++ b/gcc/config/i386/cygwin.h
> @@ -57,7 +57,7 @@ along with GCC; see the file COPYING3.  If not see
>
>  #undef ENDFILE_SPEC
>  #define ENDFILE_SPEC \
> -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s}\
> +  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
>     %{!shared:%:if-exists(default-manifest.o%s)}\
>     %{fvtable-verify=none:%s; \
>      fvtable-verify=preinit:vtv_end.o%s; \
> diff --git a/gcc/config/i386/darwin.h b/gcc/config/i386/darwin.h
> index a55f6b2b874..2f773924d6e 100644
> --- a/gcc/config/i386/darwin.h
> +++ b/gcc/config/i386/darwin.h
> @@ -109,8 +109,8 @@ along with GCC; see the file COPYING3.  If not see
>  "%{!force_cpusubtype_ALL:-force_cpusubtype_ALL} "
>
>  #undef ENDFILE_SPEC
> -#define ENDFILE_SPEC \
> -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
> +#define ENDFILE_SPEC
> +\  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
>     %{mpc32:crtprec32.o%s} \
>     %{mpc64:crtprec64.o%s} \
>     %{mpc80:crtprec80.o%s}" TM_DESTRUCTOR
> diff --git a/gcc/config/i386/gnu-user-common.h b/gcc/config/i386/gnu-user-common.h
> index 23b54c5be52..3d2a33f1714 100644
> --- a/gcc/config/i386/gnu-user-common.h
> +++ b/gcc/config/i386/gnu-user-common.h
> @@ -47,7 +47,7 @@ along with GCC; see the file COPYING3.  If not see
>
>  /* Similar to standard GNU userspace, but adding -ffast-math support.  */
>  #define GNU_USER_TARGET_MATHFILE_SPEC \
> -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
> +  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
>     %{mpc32:crtprec32.o%s} \
>     %{mpc64:crtprec64.o%s} \
>     %{mpc80:crtprec80.o%s}"
> diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> index a3675e515bc..5cfb7cdcbc2 100644
> --- a/gcc/config/i386/i386.opt
> +++ b/gcc/config/i386/i386.opt
> @@ -420,6 +420,10 @@ mpc80
>  Target RejectNegative
>  Set 80387 floating-point precision to 80-bit.
>
> +mdaz-ftz
> +Target
> +Set the FTZ and DAZ Flags.
> +
>  mpreferred-stack-boundary=
>  Target RejectNegative Joined UInteger Var(ix86_preferred_stack_boundary_arg)
>  Attempt to keep stack aligned to this power of 2.
> diff --git a/gcc/config/i386/mingw32.h b/gcc/config/i386/mingw32.h
> index d3ca0cd0279..ddbe6a4054b 100644
> --- a/gcc/config/i386/mingw32.h
> +++ b/gcc/config/i386/mingw32.h
> @@ -197,7 +197,7 @@ along with GCC; see the file COPYING3.  If not see
>
>  #undef ENDFILE_SPEC
>  #define ENDFILE_SPEC \
> -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
> +  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
>     %{!shared:%:if-exists(default-manifest.o%s)}\
>     %{fvtable-verify=none:%s; \
>      fvtable-verify=preinit:vtv_end.o%s; \
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index cb83dd8a1cc..87eedfffa6c 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -1434,7 +1434,7 @@ See RS/6000 and PowerPC Options.
>  -m96bit-long-double  -mlong-double-64  -mlong-double-80  -mlong-double-128 @gol
>  -mregparm=@var{num}  -msseregparm @gol
>  -mveclibabi=@var{type}  -mvect8-ret-in-mem @gol
> --mpc32  -mpc64  -mpc80  -mstackrealign @gol
> +-mpc32  -mpc64  -mpc80 -mdaz-ftz -mstackrealign @gol
>  -momit-leaf-frame-pointer  -mno-red-zone  -mno-tls-direct-seg-refs @gol
>  -mcmodel=@var{code-model}  -mabi=@var{name}  -maddress-mode=@var{mode} @gol
>  -m32  -m64  -mx32  -m16  -miamcu  -mlarge-data-threshold=@var{num} @gol
> @@ -32078,6 +32078,15 @@ are enabled by default; routines in such libraries could suffer significant
>  loss of accuracy, typically through so-called ``catastrophic cancellation'',
>  when this option is used to set the precision to less than extended precision.
>
> +@item -mdaz-ftz
> +@opindex mdaz-ftz
> +
> +The flush-to-zero (FTZ) and denormals-are-zero (DAZ) flags in the MXCSR register
> +are used to control floating-point calculations.SSE and AVX instructions
> +including scalar and vector instructions could benefit from enabling the FTZ
> +and DAZ flags when @option{-mdaz-ftz} is specified. Don't set FTZ/DAZ flags
> +when @option{-mno-daz-ftz} is specified.
> +
>  @item -mstackrealign
>  @opindex mstackrealign
>  Realign the stack at entry.  On the x86, the @option{-mstackrealign}
> --
> 2.39.1.388.g2fc9e9ca3c
>

On Fri, May 12, 2023 at 1:43 PM Hongtao Liu <crazylht@gmail.com> wrote:
>
> On Wed, May 10, 2023 at 5:10 PM liuhongt <hongtao.liu@intel.com> wrote:
> >
> > > The quoted patch shows -shared in context and  you didn't post a
> > > backport version
> > > to look at.  But yes, we shouldn't change -shared behavior on a
> > > branch, even less so make it
> > > inconsistent between targets.
> > Here's the patch.
> >
> > Bootstrapped and regtested on x86_64-pc-linux-gnu{-m32,}.
> > Ok for GCC 11/12 backport?
> I'm going to push the patch next week if there's no objection.
pushed to gcc-11/gcc-12 branch.
> >
> >     if (mdaz-ftz)
> >       link crtfastmath.o
> >     else if ((Ofast || ffast-math || funsafe-math-optimizations)
> >              && !mno-daz-ftz)
> >       link crtfastmath.o
> >     else
> >       Don't link crtfastmath.o
> >
> > gcc/ChangeLog:
> >
> >         * config/i386/cygwin.h (ENDFILE_SPEC): Link crtfastmath.o
> >         whenever -mdaz-ftz is specified. Don't link crtfastmath.o
> >         when -mno-daz-ftz is specified.
> >         * config/i386/darwin.h (ENDFILE_SPEC): Ditto.
> >         * config/i386/gnu-user-common.h
> >         (GNU_USER_TARGET_MATHFILE_SPEC): Ditto.
> >         * config/i386/mingw32.h (ENDFILE_SPEC): Ditto.
> >         * config/i386/i386.opt (mdaz-ftz): New option.
> >         * doc/invoke.texi (x86 options): Document mftz-daz.
> > ---
> >  gcc/config/i386/cygwin.h          |  2 +-
> >  gcc/config/i386/darwin.h          |  4 ++--
> >  gcc/config/i386/gnu-user-common.h |  2 +-
> >  gcc/config/i386/i386.opt          |  4 ++++
> >  gcc/config/i386/mingw32.h         |  2 +-
> >  gcc/doc/invoke.texi               | 11 ++++++++++-
> >  6 files changed, 19 insertions(+), 6 deletions(-)
> >
> > diff --git a/gcc/config/i386/cygwin.h b/gcc/config/i386/cygwin.h
> > index d06eda369cf..5412c5d4479 100644
> > --- a/gcc/config/i386/cygwin.h
> > +++ b/gcc/config/i386/cygwin.h
> > @@ -57,7 +57,7 @@ along with GCC; see the file COPYING3.  If not see
> >
> >  #undef ENDFILE_SPEC
> >  #define ENDFILE_SPEC \
> > -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s}\
> > +  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
> >     %{!shared:%:if-exists(default-manifest.o%s)}\
> >     %{fvtable-verify=none:%s; \
> >      fvtable-verify=preinit:vtv_end.o%s; \
> > diff --git a/gcc/config/i386/darwin.h b/gcc/config/i386/darwin.h
> > index a55f6b2b874..2f773924d6e 100644
> > --- a/gcc/config/i386/darwin.h
> > +++ b/gcc/config/i386/darwin.h
> > @@ -109,8 +109,8 @@ along with GCC; see the file COPYING3.  If not see
> >  "%{!force_cpusubtype_ALL:-force_cpusubtype_ALL} "
> >
> >  #undef ENDFILE_SPEC
> > -#define ENDFILE_SPEC \
> > -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
> > +#define ENDFILE_SPEC
> > +\  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
> >     %{mpc32:crtprec32.o%s} \
> >     %{mpc64:crtprec64.o%s} \
> >     %{mpc80:crtprec80.o%s}" TM_DESTRUCTOR
> > diff --git a/gcc/config/i386/gnu-user-common.h b/gcc/config/i386/gnu-user-common.h
> > index 23b54c5be52..3d2a33f1714 100644
> > --- a/gcc/config/i386/gnu-user-common.h
> > +++ b/gcc/config/i386/gnu-user-common.h
> > @@ -47,7 +47,7 @@ along with GCC; see the file COPYING3.  If not see
> >
> >  /* Similar to standard GNU userspace, but adding -ffast-math support.  */
> >  #define GNU_USER_TARGET_MATHFILE_SPEC \
> > -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
> > +  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
> >     %{mpc32:crtprec32.o%s} \
> >     %{mpc64:crtprec64.o%s} \
> >     %{mpc80:crtprec80.o%s}"
> > diff --git a/gcc/config/i386/i386.opt b/gcc/config/i386/i386.opt
> > index a3675e515bc..5cfb7cdcbc2 100644
> > --- a/gcc/config/i386/i386.opt
> > +++ b/gcc/config/i386/i386.opt
> > @@ -420,6 +420,10 @@ mpc80
> >  Target RejectNegative
> >  Set 80387 floating-point precision to 80-bit.
> >
> > +mdaz-ftz
> > +Target
> > +Set the FTZ and DAZ Flags.
> > +
> >  mpreferred-stack-boundary=
> >  Target RejectNegative Joined UInteger Var(ix86_preferred_stack_boundary_arg)
> >  Attempt to keep stack aligned to this power of 2.
> > diff --git a/gcc/config/i386/mingw32.h b/gcc/config/i386/mingw32.h
> > index d3ca0cd0279..ddbe6a4054b 100644
> > --- a/gcc/config/i386/mingw32.h
> > +++ b/gcc/config/i386/mingw32.h
> > @@ -197,7 +197,7 @@ along with GCC; see the file COPYING3.  If not see
> >
> >  #undef ENDFILE_SPEC
> >  #define ENDFILE_SPEC \
> > -  "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} \
> > +  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!mno-daz-ftz:crtfastmath.o%s}} \
> >     %{!shared:%:if-exists(default-manifest.o%s)}\
> >     %{fvtable-verify=none:%s; \
> >      fvtable-verify=preinit:vtv_end.o%s; \
> > diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> > index cb83dd8a1cc..87eedfffa6c 100644
> > --- a/gcc/doc/invoke.texi
> > +++ b/gcc/doc/invoke.texi
> > @@ -1434,7 +1434,7 @@ See RS/6000 and PowerPC Options.
> >  -m96bit-long-double  -mlong-double-64  -mlong-double-80  -mlong-double-128 @gol
> >  -mregparm=@var{num}  -msseregparm @gol
> >  -mveclibabi=@var{type}  -mvect8-ret-in-mem @gol
> > --mpc32  -mpc64  -mpc80  -mstackrealign @gol
> > +-mpc32  -mpc64  -mpc80 -mdaz-ftz -mstackrealign @gol
> >  -momit-leaf-frame-pointer  -mno-red-zone  -mno-tls-direct-seg-refs @gol
> >  -mcmodel=@var{code-model}  -mabi=@var{name}  -maddress-mode=@var{mode} @gol
> >  -m32  -m64  -mx32  -m16  -miamcu  -mlarge-data-threshold=@var{num} @gol
> > @@ -32078,6 +32078,15 @@ are enabled by default; routines in such libraries could suffer significant
> >  loss of accuracy, typically through so-called ``catastrophic cancellation'',
> >  when this option is used to set the precision to less than extended precision.
> >
> > +@item -mdaz-ftz
> > +@opindex mdaz-ftz
> > +
> > +The flush-to-zero (FTZ) and denormals-are-zero (DAZ) flags in the MXCSR register
> > +are used to control floating-point calculations.SSE and AVX instructions
> > +including scalar and vector instructions could benefit from enabling the FTZ
> > +and DAZ flags when @option{-mdaz-ftz} is specified. Don't set FTZ/DAZ flags
> > +when @option{-mno-daz-ftz} is specified.
> > +
> >  @item -mstackrealign
> >  @opindex mstackrealign
> >  Realign the stack at entry.  On the x86, the @option{-mstackrealign}
> > --
> > 2.39.1.388.g2fc9e9ca3c
> >
>
>
> --
> BR,
> Hongtao