[glibc] fegetenv_and_set_rn now uses the builtins provided by GCC.

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4eac1825ed92e88c192abb436412d5fb84ddd854

commit 4eac1825ed92e88c192abb436412d5fb84ddd854
Author: Manjunath Matti <mmatti@linux.ibm.com>
Date:   Sat Sep 23 10:49:51 2023 -0500

    fegetenv_and_set_rn now uses the builtins provided by GCC.
    
    On powerpc, SET_RESTORE_ROUND uses inline assembly to optimize the
    prologue get/save/set rounding mode operations for POWER9 and
    later by using 'mffscrn' where possible, this was introduced by
    commit f1c56cdff09f650ad721fae026eb6a3651631f3d.
    
    GCC version 14 onwards supports builtins as __builtin_set_fpscr_rn
    which now returns the FPSCR fields in a double. This feature is
    available on Power9 when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro
    is defined.
    GCC commit ef3bbc69d15707e4db6e2f198c621effb636cc26 adds
    this feature.
    
    Changes are done to use __builtin_set_fpscr_rn instead of mffscrn
    or mffscrni in __fe_mffscrn(rn).
    
    Suggested-by: Carl Love <cel@us.ibm.com>
    Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

Diff:
---
 sysdeps/powerpc/fpu/fenv_libc.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/sysdeps/powerpc/fpu/fenv_libc.h b/sysdeps/powerpc/fpu/fenv_libc.h
index fa5e1c697e..a2a12d914b 100644
--- a/sysdeps/powerpc/fpu/fenv_libc.h
+++ b/sysdeps/powerpc/fpu/fenv_libc.h
@@ -68,6 +68,14 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
     __fr;								\
   })
 
+/* Starting with GCC 14 __builtin_set_fpscr_rn can be used to return the
+   FPSCR fields as a double.  This support is available
+   on Power9 when the __SET_FPSCR_RN_RETURNS_FPSCR__ macro is defined.
+   To retain backward compatibility with older GCC, we still retain the
+   old inline assembly implementation.*/
+#ifdef __SET_FPSCR_RN_RETURNS_FPSCR__
+#define __fe_mffscrn(rn)  __builtin_set_fpscr_rn (rn)
+#else
 #define __fe_mffscrn(rn)						\
   ({register fenv_union_t __fr;						\
     if (__builtin_constant_p (rn))					\
@@ -83,6 +91,7 @@ extern const fenv_t *__fe_mask_env (void) attribute_hidden;
     }									\
     __fr.fenv;								\
   })
+#endif
 
 /* Like fegetenv_control, but also sets the rounding mode.  */
 #ifdef _ARCH_PWR9