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SubjectRe: [PATCH 6/8] i386: bitops: Don't mark memory as clobbered unnecessarily
Satyam Sharma wrote:
> From: Satyam Sharma <ssatyam@cse.iitk.ac.in>
>
> [6/8] i386: bitops: Don't mark memory as clobbered unnecessarily
>
> The goal is to let gcc generate good, beautiful, optimized code.
>
> But test_and_set_bit, test_and_clear_bit, __test_and_change_bit,
> and test_and_change_bit unnecessarily mark all of memory as clobbered,
> thereby preventing gcc from doing perfectly valid optimizations.
>
> The case of __test_and_change_bit() is particularly surprising, given
> that it's a variant where we don't make any guarantees at all.

__test_and_change_bit is one that you could remove the memory clobber
from.

> ---
>
> include/asm-i386/bitops.h | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/asm-i386/bitops.h b/include/asm-i386/bitops.h
> index 0f5634b..f37b8a2 100644
> --- a/include/asm-i386/bitops.h
> +++ b/include/asm-i386/bitops.h
> @@ -254,7 +254,7 @@ static inline int __test_and_change_bit(int nr, unsigned long *addr)
> __asm__ __volatile__(
> "btcl %2,%1\n\tsbbl %0,%0"
> :"=r" (oldbit),"=m" (*addr)
> - :"r" (nr) : "memory");
> + :"r" (nr));
> return oldbit;
> }
>


--
SUSE Labs, Novell Inc.
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