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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>
8f76f9c469