[gcc r13-4891] x86: Add a new option -mdaz-ftz to enable FTZ and DAZ flags in MXCSR.

[gcc r13-4891] x86: Add a new option -mdaz-ftz to enable FTZ and DAZ flags in MXCSR.

[hongtao Liu]

https://gcc.gnu.org/g:e54375d85d4aa5889869c2672158083b2106b623

commit r13-4891-ge54375d85d4aa5889869c2672158083b2106b623
Author: liuhongt <hongtao.liu@intel.com>
Date:   Mon Dec 12 15:43:58 2022 +0800

    x86: Add a new option -mdaz-ftz to enable FTZ and DAZ flags in MXCSR.
    
    if (mdaz-ftz)
      link crtfastmath.o
    else if ((Ofast || ffast-math || funsafe-math-optimizations)
             && !shared && !mno-daz-ftz)
      link crtfastmath.o
    else
      Don't link crtfastmath.o
    
    gcc/ChangeLog:
    
            PR target/55522
            PR target/36821
            * config/i386/gnu-user-common.h (GNU_USER_TARGET_MATHFILE_SPEC):
            Link crtfastmath.o whenever -mdaz-ftz is specified. Don't link
            crtfastmath.o when -share or -mno-daz-ftz is specified.
            * config/i386/i386.opt (mdaz-ftz): New option.
            * doc/invoke.texi (x86 options): Document mftz-daz.

Diff:
---
 gcc/config/i386/gnu-user-common.h |  2 +-
 gcc/config/i386/i386.opt          |  4 ++++
 gcc/doc/invoke.texi               | 12 +++++++++++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/gcc/config/i386/gnu-user-common.h b/gcc/config/i386/gnu-user-common.h
index 9910cd64363..f910524a6c3 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:%{!shared:crtfastmath.o%s}} \
+  "%{mdaz-ftz:crtfastmath.o%s;Ofast|ffast-math|funsafe-math-optimizations:%{!shared:%{!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 fb4e57ada7c..0b7df429734 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/doc/invoke.texi b/gcc/doc/invoke.texi
index da9ad1068fb..0bbf709e0e9 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -1433,7 +1433,7 @@ 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
@@ -32793,6 +32793,16 @@ 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} or @option{-shared} is specified, @option{-mdaz-ftz}
+will set FTZ/DAZ flags even with @option{-shared}.
+
 @item -mstackrealign
 @opindex mstackrealign
 Realign the stack at entry.  On the x86, the @option{-mstackrealign}