[glibc] arm: Enable USE_ATOMIC_COMPILER_BUILTINS (BZ #24774)

[glibc] arm: Enable USE_ATOMIC_COMPILER_BUILTINS (BZ #24774)

[Adhemerval Zanella]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=f9646d138f568ced95b29c20efdf902063c7ea96

commit f9646d138f568ced95b29c20efdf902063c7ea96
Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date:   Tue Sep 28 17:53:28 2021 +0000

    arm: Enable USE_ATOMIC_COMPILER_BUILTINS (BZ #24774)
    
    As per other architectures.  I have checked on a armv8 hardware with
    the following configurations:
    
      arm-linux-gnueabihf (gcc built with --with-float=hard --with-cpu=arm926ej-s)
      armv5-linux-gnueabihf (-march=armv5te -mfpu=vfpv3)
      armv7-linux-gnueabihf (-march=armv7-a -mfpu=vfpv3)
      armv7-thumb-linux-gnueabihf (-march=armv7-a -mfpu=vfpv3 -mthumb)
      armv7-neon-linux-gnueabihf (-march=armv7-a -mfpu=neon)
      armv7-neonhard-linux-gnueabihf (-march=armv7-a -mfpu=neon -mfloat-abi=hard)
    
    Without any regression.
    
    I haven't dig into the code, but since Linux atomic-machine.h handle
    pre-ARMv6 and ARMv6 I expect the compiler might have some small room
    to optimize.
    
    The code size also improves is most of the configurations:
    
    * master
    
       text    data     bss     dec     hex filename
    1727801    9720   37928 1775449  1b1759  arm-linux-gnueabihf/libc.so
    1691729    9720   37928 1739377  1a8a71  arm-linux-gnueabihf-armv7-disable-multi-arch/libc.so
    1725509    9720   37928 1773157  1b0e65  armv5-linux-gnueabihf/libc.so
    1700757    9720   37928 1748405  1aadb5  armv6-linux-gnueabihf/libc.so
    1698973    9720   37928 1746621  1aa6bd  armv6t2-linux-gnueabihf/libc.so
    1695481    9752   37928 1743161  1a9939  armv7-linux-gnueabihf/libc.so
    1692917    9744   37928 1740589  1a8f2d  armv7-neonhard-linux-gnueabihf/libc.so
    1692917    9744   37928 1740589  1a8f2d  armv7-neon-linux-gnueabihf/libc.so
    1225353    9752   37928 1273033  136cc9  armv7-thumb-linux-gnueabihf/libc.so
    
    * patched
    
       text    data     bss     dec     hex filename
    1726805    9720   37928 1774453  1b1375 arm-linux-gnueabihf/libc.so
    1689321    9720   37928 1736969  1a8109 arm-linux-gnueabihf-armv7-disable-multi-arch/libc.so
    1724433    9720   37928 1772081  1b0a31 armv5-linux-gnueabihf/libc.so
    1698301    9720   37928 1745949  1aa41d armv6-linux-gnueabihf/libc.so
    1696525    9720   37928 1744173  1a9d2d armv6t2-linux-gnueabihf/libc.so
    1693009    9752   37928 1740689  1a8f91 armv7-linux-gnueabihf/libc.so
    1690493    9744   37928 1738165  1a85b5 armv7-neonhard-linux-gnueabihf/libc.so
    1690493    9744   37928 1738165  1a85b5 armv7-neon-linux-gnueabihf/libc.so
    1223837    9752   37928 1271517  1366dd armv7-thumb-linux-gnueabihf/libc.so
    
    The idea is eventually move all architectures to use compiler builtins.
    
    Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
    Tested-by: Aurelien Jarno <aurelien@aurel32.net>

Diff:
---
 sysdeps/arm/atomic-machine.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sysdeps/arm/atomic-machine.h b/sysdeps/arm/atomic-machine.h
index 9524043797..e1f7731df0 100644
--- a/sysdeps/arm/atomic-machine.h
+++ b/sysdeps/arm/atomic-machine.h
@@ -17,7 +17,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #define __HAVE_64B_ATOMICS 0
-#define USE_ATOMIC_COMPILER_BUILTINS 0
+#define USE_ATOMIC_COMPILER_BUILTINS 1
 #define ATOMIC_EXCHANGE_USES_CAS 1
 
 void __arm_link_error (void);