https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106770
--- Comment #2 from Jens Seifert <jens.seifert at de dot ibm.com> ---
vec_extract(vr, 1) should extract the left element. But xxpermdi x,x,x,3
extracts the right element.
Looks like a bug in vec_extract for PPCLE and not a problem regarding
unnecessary xxpermdi.
Using assembly for the subtract:
int cmp3(double a, double b)
{
vector double va = vec_promote(a, 0);
vector double vb = vec_promote(b, 0);
vector long long vlt = (vector long long)vec_cmplt(va, vb);
vector long long vgt = (vector long long)vec_cmplt(vb, va);
vector signed long long vr;
__asm__ volatile("vsubudm %0,%1,%2":"=v"(vr):"v"(vlt),"v"(vgt):);
//vector signed long long vr = vec_sub(vlt, vgt);
return vec_extract(vr, 1);
}
generates:
_Z4cmp3dd:
.LFB2:
.cfi_startproc
xxpermdi 1,1,1,0
xxpermdi 2,2,2,0
xvcmpgtdp 32,2,1
xvcmpgtdp 33,1,2
#APP
# 34 "cmpdouble.C" 1
vsubudm 0,0,1
# 0 "" 2
#NO_APP
mfvsrd 3,32
extsw 3,3
"
Looks like the compile knows about the vec_promote doing splat and at the end
extracts the non-preferred right element instead of the expected left element.
