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bitops/non-atomic: make @nr unsigned to avoid any DIV 

signed math causes generation of costlier instructions such as DIV when
they could be done by barrerl shifter.

Worse part is this is not caught by things like bloat-o-meter since
instruction length / symbols are typically same size.

e.g.

stock (signed math)
__________________

919b4614 <test_taint>:
919b4614:	div	r2,r0,0x20
                ^^^
919b4618:	add2	r2,0x920f6050,r2
919b4620:	ld_s	r2,[r2,0]
919b4622:	lsr	r0,r2,r0
919b4626:	j_s.d	[blink]
919b4628:	bmsk_s	r0,r0,0
919b462a:	nop_s

(patched) unsigned math
__________________

919b4614 <test_taint>:
919b4614:	lsr	r2,r0,0x5  @nr/32
                ^^^
919b4618:	add2	r2,0x920f6050,r2
919b4620:	ld_s	r2,[r2,0]
919b4622:	lsr	r0,r2,r0     #test_bit()
919b4626:	j_s.d	[blink]
919b4628:	bmsk_s	r0,r0,0
919b462a:	nop_s

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
This commit is contained in:
Vineet Gupta 2021-08-05 12:14:08 -07:00 committed by Arnd Bergmann
parent a71bfc0079
commit 8f76f9c469
1 changed files with 7 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
include/asm-generic/bitops/non-atomic.h
View File

@ -13,7 +13,7 @@
* If it's called on the same region of memory simultaneously, the effect
* may be that only one operation succeeds.
*/
static inline void __set_bit(int nr, volatile unsigned long *addr)
static inline void __set_bit(unsigned int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
@ -21,7 +21,7 @@ static inline void __set_bit(int nr, volatile unsigned long *addr)
*p |= mask;
}
static inline void __clear_bit(int nr, volatile unsigned long *addr)
static inline void __clear_bit(unsigned int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
@ -38,7 +38,7 @@ static inline void __clear_bit(int nr, volatile unsigned long *addr)
* If it's called on the same region of memory simultaneously, the effect
* may be that only one operation succeeds.
*/
static inline void __change_bit(int nr, volatile unsigned long *addr)
static inline void __change_bit(unsigned int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
@ -55,7 +55,7 @@ static inline void __change_bit(int nr, volatile unsigned long *addr)
* If two examples of this operation race, one can appear to succeed
* but actually fail. You must protect multiple accesses with a lock.
*/
static inline int __test_and_set_bit(int nr, volatile unsigned long *addr)
static inline int __test_and_set_bit(unsigned int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
@ -74,7 +74,7 @@ static inline int __test_and_set_bit(int nr, volatile unsigned long *addr)
* If two examples of this operation race, one can appear to succeed
* but actually fail. You must protect multiple accesses with a lock.
*/
static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr)
static inline int __test_and_clear_bit(unsigned int nr, volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
@ -85,7 +85,7 @@ static inline int __test_and_clear_bit(int nr, volatile unsigned long *addr)
}
/* WARNING: non atomic and it can be reordered! */
static inline int __test_and_change_bit(int nr,
static inline int __test_and_change_bit(unsigned int nr,
volatile unsigned long *addr)
{
unsigned long mask = BIT_MASK(nr);
@ -101,7 +101,7 @@ static inline int __test_and_change_bit(int nr,
* @nr: bit number to test
* @addr: Address to start counting from
*/
static inline int test_bit(int nr, const volatile unsigned long *addr)
static inline int test_bit(unsigned int nr, const volatile unsigned long *addr)
{
return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
}