https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79218
Bug ID: 79218
Summary: Missed swap optimization on powerpc64le simple test
case
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: bergner at gcc dot gnu.org
Target Milestone: ---
The following test case has some unnecessary swaps:
bergner@genoa:~/gcc/BUGS$ cat ptr5.i
void
ptr5 (__int128_t *dst, __int128_t *src)
{
*dst = ~*src;
}
bergner@genoa:~/gcc/BUGS$ gcc7 -O2 -mcpu=power8 -S ptr5.i
bergner@genoa:~/gcc/BUGS$ cat ptr5.s
ptr5:
lxvd2x 0,0,4
xxpermdi 0,0,0,2
xxlnor 0,0,0
xxpermdi 0,0,0,2
stxvd2x 0,0,3
blr
This is still better than what GCC6 which produces:
bergner@genoa:~/gcc/BUGS$ gcc6 -O2 -mcpu=power8 -S ptr5.i
bergner@genoa:~/gcc/BUGS$ cat ptr5.s
ptr5:
ld 10,0(4)
ld 11,8(4)
not 10,10
not 11,11
std 10,0(3)
std 11,8(3)
blr
I'll note that GCC7 using -mcpu=power9 does not have any swaps due to the new
endian friendly dform load/stores:
bergner@genoa:~/gcc/BUGS$ gcc7 -O2 -mcpu=power9 -S ptr5.i
bergner@genoa:~/gcc/BUGS$ cat ptr5.s
ptr5:
lxv 0,0(4)
xxlnor 0,0,0
stxv 0,0(3)
blr
