Warnings for redundant imports doesn't take name shadowing into account (Regression)

Reproduction:

module Log where

import Prelude hiding (log)

f :: ()
f = log where log = ()

Compiling this with -Wall On GHC 7.8.2:

> ghc Log.hs -Wall
[1 of 1] Compiling Log              ( Log.hs, Log.o )

Log.hs:3:1: Warning:
    The import of ‘Prelude’ is redundant
      except perhaps to import instances from ‘Prelude’
    To import instances alone, use: import Prelude()

The suggestion is incorrect since removing the import statement gives the following warning:

Log.hs:4:15: Warning:
    This binding for ‘log’ shadows the existing binding
      imported from ‘Prelude’ at Log.hs:1:8-10
      (and originally defined in ‘GHC.Float’)

On GHC 7.6.3 the Reproduction does not give any warnings (which is correct).

Trac metadata

Trac field	Value
Version	7.8.2
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture