refine situations where speculation is allowed in coreprep

Author: luite

overlays/patches/ghc/ghc-9.4-9.6-9.8-disable-coreprep-spec-eval.patch

@@ -1,13 +1,20 @@
 diff --git a/compiler/GHC/CoreToStg/Prep.hs b/compiler/GHC/CoreToStg/Prep.hs
-index c463f41121..58b1d957c8 100644
+index c463f41121..3673b94991 100644
 --- a/compiler/GHC/CoreToStg/Prep.hs
 +++ b/compiler/GHC/CoreToStg/Prep.hs
-@@ -1759,7 +1759,7 @@ data OkToSpec
+@@ -1785,7 +1785,14 @@ mkFloat env dmd is_unlifted bndr rhs
+   where
+     is_hnf      = exprIsHNF rhs
+     is_strict   = isStrUsedDmd dmd
+-    ok_for_spec = exprOkForSpecEval (not . is_rec_call) rhs
++    ok_for_spec = exprOkForSpecEval fun_ok_for_spec rhs
++    fun_ok_for_spec i
++      | is_rec_call i = False
++      | otherwise     =
++          case idDetails i of
++                  DFunId {}        -> False
++                  DataConWorkId {} -> False
++                  _                -> True
+     is_rec_call = (`elemUnVarSet` cpe_rec_ids env)
 
- mkFloat :: CorePrepEnv -> Demand -> Bool -> Id -> CpeRhs -> FloatingBind
- mkFloat env dmd is_unlifted bndr rhs
--  | is_strict || ok_for_spec -- See Note [Speculative evaluation]
-+  | is_strict {-|| ok_for_spec-} -- See Note [Speculative evaluation]
-   , not is_hnf  = FloatCase rhs bndr DEFAULT [] ok_for_spec
-     -- Don't make a case for a HNF binding, even if it's strict
-     -- Otherwise we get  case (\x -> e) of ...!
+ emptyFloats :: Floats