| Message ID | 20220617144031.2549432-5-alexandr.lobakin@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | bitops: let optimize out non-atomic bitops on compile-time constants | expand |
On Fri, 17 Jun 2022 at 19:21, Alexander Lobakin <alexandr.lobakin@intel.com> wrote: > > Define const_*() variants of the non-atomic bitops to be used when > the input arguments are compile-time constants, so that the compiler > will be always able to resolve those to compile-time constants as > well. Those are mostly direct aliases for generic_*() with one > exception for const_test_bit(): the original one is declared > atomic-safe and thus doesn't discard the `volatile` qualifier, so > in order to let optimize code, define it separately disregarding > the qualifier. > Add them to the compile-time type checks as well just in case. > > Suggested-by: Marco Elver <elver@google.com> > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> Reviewed-by: Marco Elver <elver@google.com> > --- > .../asm-generic/bitops/generic-non-atomic.h | 31 +++++++++++++++++++ > include/linux/bitops.h | 1 + > 2 files changed, 32 insertions(+) > > diff --git a/include/asm-generic/bitops/generic-non-atomic.h b/include/asm-generic/bitops/generic-non-atomic.h > index b85b8a2ac239..3d5ebd24652b 100644 > --- a/include/asm-generic/bitops/generic-non-atomic.h > +++ b/include/asm-generic/bitops/generic-non-atomic.h > @@ -127,4 +127,35 @@ generic_test_bit(unsigned long nr, const volatile unsigned long *addr) > return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1))); > } > > +/* > + * const_*() definitions provide good compile-time optimizations when > + * the passed arguments can be resolved at compile time. > + */ > +#define const___set_bit generic___set_bit > +#define const___clear_bit generic___clear_bit > +#define const___change_bit generic___change_bit > +#define const___test_and_set_bit generic___test_and_set_bit > +#define const___test_and_clear_bit generic___test_and_clear_bit > +#define const___test_and_change_bit generic___test_and_change_bit > + > +/** > + * const_test_bit - Determine whether a bit is set > + * @nr: bit number to test > + * @addr: Address to start counting from > + * > + * A version of generic_test_bit() which discards the `volatile` qualifier to > + * allow a compiler to optimize code harder. Non-atomic and to be called only > + * for testing compile-time constants, e.g. by the corresponding macros, not > + * directly from "regular" code. > + */ > +static __always_inline bool > +const_test_bit(unsigned long nr, const volatile unsigned long *addr) > +{ > + 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 */ > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index 87087454a288..d393297287d5 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -37,6 +37,7 @@ extern unsigned long __sw_hweight64(__u64 w); > /* Check that the bitops prototypes are sane */ > #define __check_bitop_pr(name) \ > static_assert(__same_type(arch_##name, generic_##name) && \ > + __same_type(const_##name, generic_##name) && \ > __same_type(name, generic_##name)) > > __check_bitop_pr(__set_bit); > -- > 2.36.1 >
On Fri, Jun 17, 2022 at 04:40:28PM +0200, Alexander Lobakin wrote: > Define const_*() variants of the non-atomic bitops to be used when > the input arguments are compile-time constants, so that the compiler > will be always able to resolve those to compile-time constants as > well. Those are mostly direct aliases for generic_*() with one > exception for const_test_bit(): the original one is declared > atomic-safe and thus doesn't discard the `volatile` qualifier, so > in order to let optimize code, define it separately disregarding > the qualifier. > Add them to the compile-time type checks as well just in case. Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > Suggested-by: Marco Elver <elver@google.com> > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> > --- > .../asm-generic/bitops/generic-non-atomic.h | 31 +++++++++++++++++++ > include/linux/bitops.h | 1 + > 2 files changed, 32 insertions(+) > > diff --git a/include/asm-generic/bitops/generic-non-atomic.h b/include/asm-generic/bitops/generic-non-atomic.h > index b85b8a2ac239..3d5ebd24652b 100644 > --- a/include/asm-generic/bitops/generic-non-atomic.h > +++ b/include/asm-generic/bitops/generic-non-atomic.h > @@ -127,4 +127,35 @@ generic_test_bit(unsigned long nr, const volatile unsigned long *addr) > return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1))); > } > > +/* > + * const_*() definitions provide good compile-time optimizations when > + * the passed arguments can be resolved at compile time. > + */ > +#define const___set_bit generic___set_bit > +#define const___clear_bit generic___clear_bit > +#define const___change_bit generic___change_bit > +#define const___test_and_set_bit generic___test_and_set_bit > +#define const___test_and_clear_bit generic___test_and_clear_bit > +#define const___test_and_change_bit generic___test_and_change_bit > + > +/** > + * const_test_bit - Determine whether a bit is set > + * @nr: bit number to test > + * @addr: Address to start counting from > + * > + * A version of generic_test_bit() which discards the `volatile` qualifier to > + * allow a compiler to optimize code harder. Non-atomic and to be called only > + * for testing compile-time constants, e.g. by the corresponding macros, not > + * directly from "regular" code. > + */ > +static __always_inline bool > +const_test_bit(unsigned long nr, const volatile unsigned long *addr) > +{ > + 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 */ > diff --git a/include/linux/bitops.h b/include/linux/bitops.h > index 87087454a288..d393297287d5 100644 > --- a/include/linux/bitops.h > +++ b/include/linux/bitops.h > @@ -37,6 +37,7 @@ extern unsigned long __sw_hweight64(__u64 w); > /* Check that the bitops prototypes are sane */ > #define __check_bitop_pr(name) \ > static_assert(__same_type(arch_##name, generic_##name) && \ > + __same_type(const_##name, generic_##name) && \ > __same_type(name, generic_##name)) > > __check_bitop_pr(__set_bit); > -- > 2.36.1 >
diff --git a/include/asm-generic/bitops/generic-non-atomic.h b/include/asm-generic/bitops/generic-non-atomic.h index b85b8a2ac239..3d5ebd24652b 100644 --- a/include/asm-generic/bitops/generic-non-atomic.h +++ b/include/asm-generic/bitops/generic-non-atomic.h @@ -127,4 +127,35 @@ generic_test_bit(unsigned long nr, const volatile unsigned long *addr) return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1))); } +/* + * const_*() definitions provide good compile-time optimizations when + * the passed arguments can be resolved at compile time. + */ +#define const___set_bit generic___set_bit +#define const___clear_bit generic___clear_bit +#define const___change_bit generic___change_bit +#define const___test_and_set_bit generic___test_and_set_bit +#define const___test_and_clear_bit generic___test_and_clear_bit +#define const___test_and_change_bit generic___test_and_change_bit + +/** + * const_test_bit - Determine whether a bit is set + * @nr: bit number to test + * @addr: Address to start counting from + * + * A version of generic_test_bit() which discards the `volatile` qualifier to + * allow a compiler to optimize code harder. Non-atomic and to be called only + * for testing compile-time constants, e.g. by the corresponding macros, not + * directly from "regular" code. + */ +static __always_inline bool +const_test_bit(unsigned long nr, const volatile unsigned long *addr) +{ + 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 */ diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 87087454a288..d393297287d5 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -37,6 +37,7 @@ extern unsigned long __sw_hweight64(__u64 w); /* Check that the bitops prototypes are sane */ #define __check_bitop_pr(name) \ static_assert(__same_type(arch_##name, generic_##name) && \ + __same_type(const_##name, generic_##name) && \ __same_type(name, generic_##name)) __check_bitop_pr(__set_bit);
Define const_*() variants of the non-atomic bitops to be used when the input arguments are compile-time constants, so that the compiler will be always able to resolve those to compile-time constants as well. Those are mostly direct aliases for generic_*() with one exception for const_test_bit(): the original one is declared atomic-safe and thus doesn't discard the `volatile` qualifier, so in order to let optimize code, define it separately disregarding the qualifier. Add them to the compile-time type checks as well just in case. Suggested-by: Marco Elver <elver@google.com> Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> --- .../asm-generic/bitops/generic-non-atomic.h | 31 +++++++++++++++++++ include/linux/bitops.h | 1 + 2 files changed, 32 insertions(+)