------- Comment #8 from rearnsha at arm dot com 2010-02-08 16:30 -------
Subject: Re: [arm] Combine cannot do its job because
immediate operand is used instead of register
On Mon, 2010-02-08 at 16:11 +0000, steven at gcc dot gnu dot org wrote:
> Can someone please explain what the expected code is?
Something like
stmfd sp!, {r3, r4, r5, lr}
mov r4, r0
mov r5, #255
mov r1, r4, lsr #24
mov r0, #8
bl func
and r1, r5, r4, lsr #16
mov r0, #8
bl func
mov r1, r5, r4, lsr #8
mov r0, #8
ldmfd sp!, {r3, r4, r5, lr}
b func
By putting 255 into a register we add one instruction, but remove 2; so
save one overall. This is one of the rare cases where an immediate is
actually more expensive on ARM than using a register.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=9760
