[x86] avoid 256-bit andnp that requires insert/extract with AVX1 (PR37449)

[x86] avoid 256-bit andnp that requires insert/extract with AVX1 (PR37449)

This is the final (I hope!) problem pattern mentioned in PR37749:
https://bugs.llvm.org/show_bug.cgi?id=37749

We are trying to avoid an AVX1 sinkhole caused by having 256-bit bitwise logic ops but no other 256-bit integer ops.
We've already solved the simple logic ops, but 'andn' is an x86 special. I looked at alternative solutions like
extending the generic DAG combine or trying to wait until the ANDNP node is created, but those are bigger patches
that can over-reach. Ie, splitting to 128-bit does not look like a win in most cases with >1 256-bit op.

The pattern matching is cluttered with bitcasts because of our i64 element canonicalization. For the affected test,
we have this vector-type-legalized sequence:

        t29: v8i32 = concat_vectors t27, t28
      t30: v4i64 = bitcast t29
        t18: v8i32 = BUILD_VECTOR Constant:i32<-1>, Constant:i32<-1>, ...
      t31: v4i64 = bitcast t18
    t32: v4i64 = xor t30, t31
      t9: v8i32 = BUILD_VECTOR Constant:i32<255>, Constant:i32<255>, ...
    t34: v4i64 = bitcast t9
  t35: v4i64 = and t32, t34
t36: v8i32 = bitcast t35
      t37: v4i32 = extract_subvector t36, Constant:i64<0>
      t38: v4i32 = extract_subvector t36, Constant:i64<4>

Differential Revision: https://reviews.llvm.org/D52318

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343008 91177308-0d34-0410-b5e6-96231b3b80d8