From: Robin Murphy Date: Fri, 12 May 2017 12:48:41 +0000 (+0100) Subject: arm64: Remove redundant mov from LL/SC cmpxchg X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=8df728e1ae614f592961e51f65d3e3212ede5a75;p=openwrt%2Fstaging%2Fblogic.git arm64: Remove redundant mov from LL/SC cmpxchg The cmpxchg implementation introduced by commit c342f78217e8 ("arm64: cmpxchg: patch in lse instructions when supported by the CPU") performs an apparently redundant register move of [old] to [oldval] in the success case - it always uses the same register width as [oldval] was originally loaded with, and is only executed when [old] and [oldval] are known to be equal anyway. The only effect it seemingly does have is to take up a surprising amount of space in the kernel text, as removing it reveals: text data bss dec hex filename 12426658 1348614 4499749 18275021 116dacd vmlinux.o.new 12429238 1348614 4499749 18277601 116e4e1 vmlinux.o.old Reviewed-by: Will Deacon Signed-off-by: Robin Murphy Signed-off-by: Catalin Marinas --- diff --git a/arch/arm64/include/asm/atomic_ll_sc.h b/arch/arm64/include/asm/atomic_ll_sc.h index f819fdcff1ac..f5a2d09afb38 100644 --- a/arch/arm64/include/asm/atomic_ll_sc.h +++ b/arch/arm64/include/asm/atomic_ll_sc.h @@ -264,7 +264,6 @@ __LL_SC_PREFIX(__cmpxchg_case_##name(volatile void *ptr, \ " st" #rel "xr" #sz "\t%w[tmp], %" #w "[new], %[v]\n" \ " cbnz %w[tmp], 1b\n" \ " " #mb "\n" \ - " mov %" #w "[oldval], %" #w "[old]\n" \ "2:" \ : [tmp] "=&r" (tmp), [oldval] "=&r" (oldval), \ [v] "+Q" (*(unsigned long *)ptr) \