My profiling showed that the BinTree operations were responsible for about 60% of the CPU time when reading a large .gfo file. Replacing BinTree by Data.Map reduced this to about 6%, which meant about 50% reduction in total CPU time.

src/GF/Compile/Coding.hs

@@ -26,13 +26,12 @@ codeSourceModule co (id,moi) = case moi of
   ModMod mo -> (id, ModMod $ replaceJudgements mo (mapTree codj (jments mo)))
   _ -> (id,moi)
  where
-    codj (c,info) = (c, case info of
+    codj (c,info) = case info of
       ResOper     pty pt  -> ResOper (mapP codt pty) (mapP codt pt) 
       ResOverload es tyts -> ResOverload es [(codt ty,codt t) | (ty,t) <- tyts]
       CncCat pty pt mpr   -> CncCat pty (mapP codt pt) (mapP codt mpr)
       CncFun mty pt mpr   -> CncFun mty (mapP codt pt) (mapP codt mpr)
       _ -> info
-      )
     codt t = case t of
       K s -> K (co s)
       T ty cs -> T ty [(codp p,codt v) | (p,v) <- cs]