I understand that when someone came to visit who wasn't expected, it would have been usual for the bean a tí to say: 'If I knew you were coming, I would have spread green rushes for you' - apparently in front of the doorway. Obviously it would have been said in Irish and perhaps someone here might have heard it said or knew about this custom from an earlier generation in their family. Here's my attempt at it -

Dá mbeadh a fhios agam a bheifeá ag teacht, go spré mé luachair uaine romhat.

go mbeifeá ag teacht = that you would coming. (not a relative clause)

spréifinn luachair = I would (have) spread rushes
(subjunctive, e.g. go spré mé, is never used in such contexts.)

Go raibh maith agat

perhaps ?
Dá mbeadh a fhios agam go mbeifeá ag teacht scaipfinn luachair úr i mbéal an dorais romhat.
This is long-winded but I'm sure someone could shorten it but still keep its core meaning

What makes you think it was in front of the door? I suppose it could've been to soak up a muddy doorway.
But maybe it was for bedding.

It could well be for that as well, I wasn't sure about it. That's why I was asking. There's also the song An Binsín Luachra, which I understood to mean a small or 'thin' bed or mattress of rushes and it reminds me of an old blues song - Make me a palett on the floor. I don't know if there's any connection there, you never know.

My first assumption would be bedding. Unless you have some other clue it is otherwise.