How to test master after breaking changes

Hello devs, Wiki page on testing says that in order to run all tests you have to install additional packages: https://ghc.haskell.org/trac/ghc/wiki/Building/RunningTests/Running#AdditionalPackages and kindly provides a command to do this: cabal install

PSA: You likely want to use -O2 for the stage1 compiler.

I've wondered for a good while if using O2 on stage1 might be worth it. So I did some measurements and it should be worth it for most cases. For a single "quick" flavour build they are more or less on equal footing. If you rebuild stage2 multiple times reusing stage1 it will be faster. If you

Re: PSA: You likely want to use -O2 for the stage1 compiler.

Thanks, Andreas! I believe, the wiki modestly tries to suggest this here: https://ghc.haskell.org/trac/ghc/wiki/Building/Using#Workingonanoptimizedstage2compiler. Maybe, it should be more insistent, e.g., by adding these numbers or moving the advice to a more visible place. Not sure. -- Best,