http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53949
--- Comment #10 from Oleg Endo <olegendo at gcc dot gnu.org> ---
I was wondering whether it would make sense to convert sequences such as
SH4 SH4A
mov.l @r15,r3 LS/2 LS/2
mul.l r2,r3 CO/4 EX/3
sts macl,r3 CO/3 LS/2
add r1,r3 EX/1 EX/1
into
mov r15,r0 MT/0 MT/1
mov.l r2,@-r15 LS/1 LS/1
lds r1,macl CO/3 LS/1
mac.l @r15+,@r0+ CO/4 CO/5
sts macl,r3 CO/3 LS/2
Looking simply at the issue cycles (the numbers above) would suggest that it's
not worth doing it, at least not if the value has to be pulled out from the mac
register immediately after the mac operation. Probably it's not beneficial to
emit a single mac insn if the data is not already in place so that it can be
reached easily with the post-inc addressing.
On the other hand something like ...
int test33 (int* x, int y, int z)
{
return x[0] * 40 + z;
}
currently compiles to:
mov.l @r4,r2
mov #40,r1
mul.l r1,r2
sts macl,r0
rts
add r6,r0
where this one maybe could be better:
mova .L40,r0
lds r6,macl
mac.l @r4+,r0+
rts
sts macl,r0
.align 2
.L40: .long 40
