diff options
| author | Vineet Gupta | 2021-08-05 12:14:08 -0700 |
|---|---|---|
| committer | Arnd Bergmann | 2021-08-14 13:07:42 +0200 |
| commit | 8f76f9c46952659dd925c21c3f62a0d05a3f3e71 (patch) | |
| tree | 804e531533b24f68c2841facdd8a6aef88997b19 /arch/arm64 | |
| parent | a71bfc0079762b4d3cb36dcc5fe6c23c806cfc8c (diff) | |
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>
Diffstat (limited to 'arch/arm64')
0 files changed, 0 insertions, 0 deletions