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s390/Kconfig: use builtin bswap

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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>
This commit is contained in:
Christian Borntraeger 2015-10-29 01:16:04 +01:00 committed by Martin Schwidefsky
parent ccc0e7dc70
commit 295d8fa961
1 changed files with 1 additions and 0 deletions
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arch/s390/Kconfig
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@ -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