Hello, I try to use GHC backend via STG. For that reason I build small STG program AST maually. So far the generated programs worked fine (compile/link/run). However I run into problems when a lifted ADT has a FloatRep argument. Interestingly it works for DoubleRep. I'm using GHC 8.6.1 64 bit to generate the code for the constructed STG AST. I wonder if I break an invariant or is this actually a bug? Is it valid to use FloatRep argument in a boxed ADT on 64 bit? I made a gist with the Haskell source and the generated Cmm code is also included. https://gist.github.com/csabahruska/e9e143390c863f7b10b0298a7ae80ac1 Working program (DoubleRep): https://gist.github.com/csabahruska/e9e143390c863f7b10b0298a7ae80ac1#file-st... Wrong program (FloatRep): https://gist.github.com/csabahruska/e9e143390c863f7b10b0298a7ae80ac1#file-st... Thanks, Csaba