Un-named plant

I think it might be valerian it spreads like crazy in my garden

I am inclined to agree with Alex7 if we are correct beware it attracts cats and it can grow to about 3-4 ft

Valerian is an old medicinal herb, used as a sleeping medication

I would get rid of it ,it is a real thug and menace, if it gets into walls it is hard to shift, and it seeds profusely.

Yes, red valerian (centranthus ruber). To prevent it seeding everywhere, you have to deadhead it every other day as it runs to seed very quickly

Despite a lot of cats in my area I've never noticed it attracting them - that is something I've heard about the true valerian, Valeriana officinalis, instead. I like it, I've got it in very shallow soil in full sun and it flowers through most of the summer. I don't mind the deadheading. Seedlings are easily dug out and since I have a lot of self-seeders in my garden anyway I just do a bit of editing to keep what I want.