diff options
| -rw-r--r-- | arch/arc/include/asm/bitops.h | 31 |
1 files changed, 18 insertions, 13 deletions
diff --git a/arch/arc/include/asm/bitops.h b/arch/arc/include/asm/bitops.h index 1a5bf07eefe2..4051e9525939 100644 --- a/arch/arc/include/asm/bitops.h +++ b/arch/arc/include/asm/bitops.h @@ -32,6 +32,20 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *m) m += nr >> 5; + /* + * ARC ISA micro-optimization: + * + * Instructions dealing with bitpos only consider lower 5 bits (0-31) + * e.g (x << 33) is handled like (x << 1) by ASL instruction + * (mem pointer still needs adjustment to point to next word) + * + * Hence the masking to clamp @nr arg can be elided in general. + * + * However if @nr is a constant (above assumed it in a register), + * and greater than 31, gcc can optimize away (x << 33) to 0, + * as overflow, given the 32-bit ISA. Thus masking needs to be done + * for constant @nr, but no code is generated due to const prop. + */ if (__builtin_constant_p(nr)) nr &= 0x1f; @@ -374,29 +388,20 @@ __test_and_change_bit(unsigned long nr, volatile unsigned long *m) * This routine doesn't need to be atomic. */ static inline int -__constant_test_bit(unsigned int nr, const volatile unsigned long *addr) -{ - return ((1UL << (nr & 31)) & - (((const volatile unsigned int *)addr)[nr >> 5])) != 0; -} - -static inline int -__test_bit(unsigned int nr, const volatile unsigned long *addr) +test_bit(unsigned int nr, const volatile unsigned long *addr) { unsigned long mask; addr += nr >> 5; - /* ARC700 only considers 5 bits in bit-fiddling insn */ + if (__builtin_constant_p(nr)) + nr &= 0x1f; + mask = 1 << nr; return ((mask & *addr) != 0); } -#define test_bit(nr, addr) (__builtin_constant_p(nr) ? \ - __constant_test_bit((nr), (addr)) : \ - __test_bit((nr), (addr))) - /* * Count the number of zeros, starting from MSB * Helper for fls( ) friends |