https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109892
Bug ID: 109892
Summary: SLP failure with explicit fma
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: amonakov at gcc dot gnu.org
Target Milestone: ---
At -O2 -mfma (x86) or -O3 (arm64) we fail to SLP-vectorize 'f', but succeed in
'g':
double f(double x[], long n)
{
double r0 = 0, r1 = 0;
for (; n; x += 2, n--) {
r0 = __builtin_fma(x[0], x[0], r0);
r1 = __builtin_fma(x[1], x[1], r1);
}
return r0 + r1;
}
static double muladd(double x, double y, double z)
{
return x * y + z;
}
double g(double x[], long n)
{
double r0 = 0, r1 = 0;
for (; n; x += 2, n--) {
r0 = muladd(x[0], x[0], r0);
r1 = muladd(x[1], x[1], r1);
}
return r0 + r1;
}
It seems we are calling vectorizable_reduction for __builtin_fma even though it
would not participate in a reduction when vectorizing for 16-byte vectors?
