Panic when using a TH splice in a do bind pattern

When compiling this file with HEAD (f656fba1):

{-# LANGUAGE TemplateHaskell #-}
module Panic where

import Language.Haskell.TH

expr :: IO Exp
expr = runQ $ do
  name <- newName "foo"
  [| do $(varP name) <- pure (); pure () |]

I get this message:

[1 of 1] Compiling Panic            ( Panic.hs, Panic.o )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.3.20170713 for x86_64-unknown-linux):
        isIrrefutableHsPat:
  $(varP name)
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable
        pprPanic, called at compiler/hsSyn/HsPat.hs:643:15 in ghc:HsPat

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

It compiles normally with GHC 8.2.1-rc2 (20170507). The bug exists in rc3 (20170704). I am unable to perform a more precise bisect.

Trac metadata

Trac field	Value
Version	8.2.1-rc3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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