The 4.0.x branch was R.I.P.ed. Commiting 4.1.x, 4.2.x, 4.3.x and 4.4.x means 4 times of efforts than 3 times. They are very similar in design, they use TreeSSA, autovectoring, etc. It's recommended to be online 4.2.x, 4.3.x and 4.4.x branches. I want to see a comparison of performances between 4.1.x, 4.2.x and 4.4.x to know how they have been evolved. ;)