/// This should never be an issue in practice as the shuffle lowering doesn't
/// produce sequences of more than 8 instructions.
///
-/// FIXME: Currently, we don't collapse instructions *into* PSHUFB. We should,
-/// and we should do so more aggressively than we form PSHUFB because once we
-/// have a PSHUFB, we might as well do as much shuffling as we can.
-///
/// FIXME: We will currently miss some cases where the redundant shuffling
/// would simplify under the threshold for PSHUFB formation because of
/// combine-ordering. To fix this, we should do the redundant instruction