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ARC: fold __builtin_constant_p() into test_bit()

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This makes test_bit() more like its siblings *_bit() routines.
Also add some comments about the constant @nr micro-optimization

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This commit is contained in:
Vineet Gupta 2014-11-07 19:19:37 +05:30
parent 0dfb8ec70f
commit de60c1a184
1 changed files with 18 additions and 13 deletions
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31
arch/arc/include/asm/bitops.h
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@ -32,6 +32,20 @@ static inline void set_bit(unsigned long nr, volatile unsigned long *m)
m += nr >> 5; 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)) if (__builtin_constant_p(nr))
nr &= 0x1f; 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. * This routine doesn't need to be atomic.
*/ */
static inline int static inline int
__constant_test_bit(unsigned int nr, const volatile unsigned long *addr) 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)
{ {
unsigned long mask; unsigned long mask;
addr += nr >> 5; addr += nr >> 5;
/* ARC700 only considers 5 bits in bit-fiddling insn */ if (__builtin_constant_p(nr))
nr &= 0x1f;
mask = 1 << nr; mask = 1 << nr;
return ((mask & *addr) != 0); 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 * Count the number of zeros, starting from MSB
* Helper for fls( ) friends * Helper for fls( ) friends