s390/Kconfig: use builtin bswap

Depending on the gcc version we can use builtin_bswap instead of
architecture functions. Doing so is better than the inline assembly
version of load reverse for two reasons:
- the sequence of load reversed, apply constant mask, save reversed can
  be optimized to load, apply reversed mask, save
- builtins are slightly better to optimize e.g. gcc instruction
  scheduler cannot optimize grouping on inline assemblies.

To enable set we have to ARCH_USE_BUILTIN_BSWAP.
bloat-o-meter results:
add/remove: 1/1 grow/shrink: 75/533 up/down: 1711/-9394 (-7683)

Suggested-by: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 44cb7de499bbe4b1b43fc4d3e30f87da251fd22f..9b9a2db0681015dcbc386ddd7d2056def0f35b1f 100644 (file)
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -101,6 +101,7 @@ config S390
        select ARCH_SAVE_PAGE_KEYS if HIBERNATION
        select ARCH_SUPPORTS_ATOMIC_RMW
        select ARCH_SUPPORTS_NUMA_BALANCING
+       select ARCH_USE_BUILTIN_BSWAP
        select ARCH_USE_CMPXCHG_LOCKREF
        select ARCH_WANTS_PROT_NUMA_PROT_NONE
        select ARCH_WANT_IPC_PARSE_VERSION