bad code for Double literals

For this program

module Foo where

foo :: [Double] -> [Double]
foo = map f
  where f x = x*(-0.5)

GHC generates the following core:

Foo.foo5 :: GHC.Integer.Type.Integer
[GblId,
 Str=DmdType,
 Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
         ConLike=True, WorkFree=True, Expandable=True,
         Guidance=IF_ARGS [] 100 0}]
Foo.foo5 = __integer 1

Foo.foo4 :: GHC.Integer.Type.Integer
[GblId,
 Str=DmdType,
 Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
         ConLike=True, WorkFree=True, Expandable=True,
         Guidance=IF_ARGS [] 100 0}]
Foo.foo4 = __integer 2

Foo.foo3 :: GHC.Types.Double
[GblId,
 Str=DmdType,
 Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=False,
         ConLike=False, WorkFree=False, Expandable=False,
         Guidance=IF_ARGS [] 51 20}]
Foo.foo3 =
  case GHC.Float.$w$cfromRational Foo.foo5 Foo.foo4
  of _ { GHC.Types.D# x_agI ->
  GHC.Types.D# (GHC.Prim.negateDouble# x_agI)
  }

Foo.foo1 :: GHC.Types.Double -> GHC.Types.Double
[GblId,
 Arity=1,
 Str=DmdType U(L)m,
 Unf=Unf{Src=InlineStable, TopLvl=True, Arity=1, Value=True,
         ConLike=True, WorkFree=True, Expandable=True,
         Guidance=ALWAYS_IF(unsat_ok=True,boring_ok=False)
         Tmpl= \ (eta_B1 [Occ=Once] :: GHC.Types.Double) ->
                 GHC.Float.timesDouble eta_B1 Foo.foo3}]
Foo.foo1 =
  \ (eta_B1 :: GHC.Types.Double) ->
    GHC.Float.timesDouble eta_B1 Foo.foo3

Foo.foo :: [GHC.Types.Double] -> [GHC.Types.Double]
[GblId,
 Arity=1,
 Str=DmdType,
 Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=0, Value=True,
         ConLike=True, WorkFree=True, Expandable=True,
         Guidance=IF_ARGS [] 20 60}]
Foo.foo =
  GHC.Base.map @ GHC.Types.Double @ GHC.Types.Double Foo.foo1

which looks pretty bad to me.

This may be related to #5731 (closed), especially as 'foo2 = map (* (-0.5))' results in much better code.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	jwlato@gmail.com
Operating system
Architecture