Re: [PATCH 3/6] bitops: define gen_test_bit() the same way as the rest of functions

Mark Rutland
2022-06-06T16:19:42Z

On Mon, Jun 06, 2022 at 01:49:04PM +0200, Alexander Lobakin wrote:
> Currently, the generic test_bit() function is defined as a one-liner
> and in case with constant bitmaps the compiler is unable to optimize
> it to a constant. At the same time, gen_test_and_*_bit() are being
> optimized pretty good.
> Define gen_test_bit() the same way as they are defined.
>
> Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>

Regardless of whether compilers prefer this, I think it's nicer to have the
structure consistent with the rest of the functions, so FWIW:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> include/asm-generic/bitops/generic-non-atomic.h | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/include/asm-generic/bitops/generic-non-atomic.h b/include/asm-generic/bitops/generic-non-atomic.h
> index 7a60adfa6e7d..202d8a3b40e1 100644
> --- a/include/asm-generic/bitops/generic-non-atomic.h
> +++ b/include/asm-generic/bitops/generic-non-atomic.h
> @@ -118,7 +118,11 @@ gen___test_and_change_bit(unsigned int nr, volatile unsigned long *addr)
> static __always_inline int
> gen_test_bit(unsigned int nr, const volatile unsigned long *addr)
> {
> - return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
> + const unsigned long *p = (const unsigned long *)addr + BIT_WORD(nr);
> + unsigned long mask = BIT_MASK(nr);
> + unsigned long val = *p;
> +
> + return !!(val & mask);
> }
>
> #endif /* __ASM_GENERIC_BITOPS_GENERIC_NON_ATOMIC_H */
> --
> 2.36.1
>