Commit 8df728e1 authored by Robin Murphy's avatar Robin Murphy Committed by Catalin Marinas
Browse files

arm64: Remove redundant mov from LL/SC cmpxchg

The cmpxchg implementation introduced by commit c342f782

 ("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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 2ea659a9
......@@ -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) \
......
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