#14790: eqTypeRep does not inline
-------------------------------------+-------------------------------------
Reporter: dfeuer | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.6.1
Component: Compiler | Version: 8.4.1-alpha2
Keywords: | Operating System: Unknown/Multiple
Architecture: | Type of failure: Runtime
Unknown/Multiple | performance bug
Test Case: | Blocked By:
Blocking: | Related Tickets:
Differential Rev(s): | Wiki Page:
-------------------------------------+-------------------------------------
GHC never seems to inline `eqTypeRep`. That's no good! It produces a
`Maybe`, which users will almost certainly want to match on immediately.
I really don't understand ''why'' it doesn't inline. It's a tiny function,
none of the functions it calls are themselves marked `INLINE`, and the
advantage to inlining seems obvious. Does the `unsafeCoerce` get in the
way somehow? If so, how can we fix it?
Example:
{{{#!hs
{-# language GADTs, ScopedTypeVariables, TypeApplications #-}
module Foo where
import Type.Reflection
foo :: forall proxy a. Typeable a => proxy a -> Bool
foo _ = case eqTypeRep (typeRep @a) (typeRep @Int) of
Just _ -> True
Nothing -> False
}}}
compiles (with `-O2`) to
{{{
foo
= \ (@ (proxy_a6tT :: * -> *))
(@ a_a6tU)
($dTypeable_a6tW :: Typeable a_a6tU) ->
let {
lvl_s6Sc :: Maybe (a_a6tU :~~: Int)
[LclId]
lvl_s6Sc
= eqTypeRep
@ *
@ *
@ a_a6tU
@ Int
($dTypeable_a6tW
`cast` (base-4.11.0.0:Data.Typeable.Internal.N:Typeable[0]
<*>_N