The select story

Hello all,

In early 2021, a transformation in InstCombine that folds ‘select i1 %a, i1 %b, i1 false’ to ‘and i1 %a, %b’ (and another one for the ‘or’ case as well) was removed because the folding was incorrect.

To explain the background about this change and a series of patches that were made, I wrote a blog post:

I appreciate many people who helped fix it! :slight_smile:


My complements both on an informative writeup, and the completion of a long and complicated effort. Thank you (and others) for all the work on this.