You can use the rerere-train script in the git repo to populate rerere from existing merges. I use this when something in a merge has regressed a big feature br

You can use the rerere-train script in the git repo to populate rerere from existing merges. I use this when something in a merge has regressed a big feature branch and I need to bisect. I can train rerere then rebase on the 2nd to latest merge-base, all while still doing no extra work if there isn't a regression.