CoreUtils: Use mightBeUnliftedType in exprIsTopLevelBindable

Also add reference from isUnliftedType to mightBeUnliftedType.

2 files changed, 6 insertions, 2 deletions

diff --git a/compiler/coreSyn/CoreUtils.hs b/compiler/coreSyn/CoreUtils.hs
index 5204d5e9f6..d3ed00f783 100644
--- a/compiler/coreSyn/CoreUtils.hs
+++ b/compiler/coreSyn/CoreUtils.hs
@@ -1880,7 +1880,9 @@ exprIsTopLevelBindable :: CoreExpr -> Type -> Bool
 -- Top-level literal strings can't even be wrapped in ticks
 --   see Note [CoreSyn top-level string literals] in CoreSyn
 exprIsTopLevelBindable expr ty
-  = not (isUnliftedType ty)
+  = not (mightBeUnliftedType ty)
+    -- Note that 'expr' may be levity polymorphic here consequently we must use
+    -- 'mightBeUnliftedType' rather than 'isUnliftedType' as the latter would panic.
   || exprIsTickedString expr
 
 -- | Check if the expression is zero or more Ticks wrapped around a literal
diff --git a/compiler/types/Type.hs b/compiler/types/Type.hs
index 94ee5af202..f574132c4f 100644
--- a/compiler/types/Type.hs
+++ b/compiler/types/Type.hs
@@ -2214,7 +2214,9 @@ isLiftedType_maybe ty = go (getRuntimeRep ty)
           | otherwise              = Nothing     -- levity polymorphic
 
 -- | See "Type#type_classification" for what an unlifted type is.
--- Panics on levity polymorphic types.
+-- Panics on levity polymorphic types; See 'mightBeUnliftedType' for
+-- a more approximate predicate that behaves better in the presence of
+-- levity polymorphism.
 isUnliftedType :: HasDebugCallStack => Type -> Bool
         -- isUnliftedType returns True for forall'd unlifted types:
         --      x :: forall a. Int#