GHC makes thunks for Integers we are strict in

We know that timesInteger is strict in both arguments:

$ ./ghc --show-iface ~/ghc/darcs/val/libraries/base/dist/build/GHC/Num.hi | grep -C2 "^timesInteger"
plusInteger :: GHC.Num.Integer -> GHC.Num.Integer -> GHC.Num.Integer
  {- Arity: 2 HasNoCafRefs Strictness: SS -}
timesInteger :: GHC.Num.Integer -> GHC.Num.Integer -> GHC.Num.Integer
  {- Arity: 2 HasNoCafRefs Strictness: SS -}
class (GHC.Base.Eq a, GHC.Show.Show a) => Num a

but given this code:

module W where

f :: Integer -> Integer
f x = let x' = x + 3
      in x' * x'

we still make a thunk for x':

$ ./ghc -c w.hs -O -fforce-recomp -ddump-simpl
==================== Tidy Core ====================
W.lvl :: GHC.Num.Integer
[GlobalId]
[NoCafRefs
 Str: DmdType]
W.lvl = GHC.Num.S# 3

W.f :: GHC.Num.Integer -> GHC.Num.Integer
[GlobalId]
[Arity 1
 NoCafRefs
 Str: DmdType S]
W.f =
  \ (x_a5h :: GHC.Num.Integer) ->
    let {
      x'_sa7 [ALWAYS Just S] :: GHC.Num.Integer
      [Str: DmdType]
      x'_sa7 = GHC.Num.plusInteger x_a5h W.lvl } in
    GHC.Num.timesInteger x'_sa7 x'_sa7

The same is true in both the 6.8 branch and the HEAD.

Trac metadata

Trac field	Value
Version	6.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown