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authorRobin Murphy <robin.murphy@arm.com>2017-05-12 13:48:41 +0100
committerCatalin Marinas <catalin.marinas@arm.com>2017-05-15 18:30:10 +0100
commit8df728e1ae614f592961e51f65d3e3212ede5a75 (patch)
treedf8284b2f7d13200752c5afbbbd98474d256af8c /arch/arm64
parent2ea659a9ef488125eb46da6eb571de5eae5c43f6 (diff)
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 <will.deacon@arm.com> Signed-off-by: Robin Murphy <robin.murphy@arm.com> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64')
-rw-r--r--arch/arm64/include/asm/atomic_ll_sc.h1
1 files changed, 0 insertions, 1 deletions
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) \