On Fri, May 01, 2015 at 05:16:30PM +0200, Peter Zijlstra wrote:
> diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
> index cfe3b954d5e4..bcf4fa77c04f 100644
> --- a/arch/x86/include/asm/bitops.h
> +++ b/arch/x86/include/asm/bitops.h
> @@ -313,6 +313,15 @@ static __always_inline int constant_test_bit(long nr,
> const volatile unsigned lo
>
> static inline int variable_test_bit(long nr, volatile const unsigned long
> *addr)
> {
> +#ifdef CC_HAVE_ASM_GOTO
> + asm_volatile_goto ("bt %1, %0\n\t"
> + "jc %l[cc_label]"
> + : : "m" (*(unsigned long *)addr), "Ir" (nr)
> + : : cc_label);
> + return 0;
> +cc_label:
> + return 1;
> +#else
I figured I'd try both jc and jnc versions:
text data bss dec hex filename
12203914 1738112 1081344 15023370 e53d0a defconfig-build/vmlinux
12204228 1738112 1081344 15023684 e53e44
defconfig-build/vmlinux-jc
12203240 1738112 1081344 15022696 e53a68
defconfig-build/vmlinux-jnc
Clearly I picked the wrong one :-) It also shows there is real value in
exposing this decision to GCC.
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