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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;
    > }
    >


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    SUSE Labs, Novell Inc.
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