Summary

undefined in inlinable functions are unintentionally evaluated if called strictly. An example:

{-# INLINE alloca #-}
alloca :: forall a b . Storable a => (Ptr a -> IO b) -> IO b
alloca  =
  allocaBytesAligned (sizeOf (undefined :: a)) (alignment (undefined :: a))

Steps to reproduce

Use Foreign.Marshal.Alloc.alloca with Strict language extension.

Expected behavior

It should allocate a memory, not evaluating undefined. If undefineds are used in inlinable functions, lazy bindings must be used explicitly for GHC 8.0 or later.

Environment

• GHC version used: 8.0 or later

Optional: