veclower: Fix up vec_shl matching of VEC_PERM_EXPR [PR100239]
The following testcase ICEs at -O0, because lower_vec_perm sees the
_1 = { 0, 0, 0, 0, 0, 0, 0, 0 };
_2 = VEC_COND_EXPR <_1, { -1, -1, -1, -1, -1, -1, -1, -1 }, { 0, 0, 0, 0, 0, 0, 0, 0 }>;
_3 = { 6, 0, 0, 0, 0, 0, 0, 0 };
_4 = VEC_PERM_EXPR <{ 0, 0, 0, 0, 0, 0, 0, 0 }, _2, _3>;
and as the ISA is SSE2, there is no support for the particular permutation
nor for variable mask permutation. But, the code to match vec_shl matches
it, because the permutation has the first operand a zero vector and the
mask picks all elements randomly from that vector.
So, in the end that isn't a vec_shl, but the permutation could be in theory
optimized into the first argument. As we keep it as is, it will fail
during expansion though, because that for vec_shl correctly requires that
it actually is a shift:
unsigned firstidx = 0;
for (unsigned int i = 0; i < nelt; i++)
{
if (known_eq (sel[i], nelt))
{
if (i == 0 || firstidx)
return NULL_RTX;
firstidx = i;
}
else if (firstidx
? maybe_ne (sel[i], nelt + i - firstidx)
: maybe_ge (sel[i], nelt))
return NULL_RTX;
}
if (firstidx == 0)
return NULL_RTX;
first = firstidx;
The if (firstidx == 0) return NULL; is what is missing a counterpart
on the lower_vec_perm side.
As with optimize != 0 we fold it in other spots, I think it is not needed
to optimize this cornercase in lower_vec_perm (which would mean we'd need
to recurse on the newly created _4 = { 0, 0, 0, 0, 0, 0, 0, 0 };
whether it is supported or not).
2021-04-27 Jakub Jelinek <jakub@redhat.com>
PR tree-optimization/100239
* tree-vect-generic.c (lower_vec_perm): Don't accept constant
permutations with all indices from the first zero element as vec_shl.
* gcc.dg/pr100239.c: New test.
(cherry picked from commit
83d26d0e1b3625ab6c2d83610a13976b52f63e0a)