GHC panic with UnliftedFFITypes+CApiFFI

The following code fails to compile with at least GHC 7.6, 7.8 and HEAD:

import GHC.Prim
import Foreign.C

type GmpLimb = CULong
type GmpSize = CLong

-- mp_limb_t mpn_add_1 (mp_limb_t *rp, const mp_limb_t *s1p, mp_size_t n, mp_limb_t s2limb)

foreign import capi unsafe "gmp.h mpn_add_1"
  c_mpn_add_1 :: MutableByteArray# s -> ByteArray# -> GmpSize -> GmpLimb -> IO GmpLimb

with the following compile error message:

ghc: panic! (the 'impossible' happened)
  (GHC version 7.9.20140704 for x86_64-unknown-linux):
	toCType MutableByteArray# s

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

Otoh, replacing capi with ccall makes the code compile just fine

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed milestone to %7.10.1

changed weight to 5

added Tbug Trac import labels

Here's a simpler example (stolen from Data.ByteString.Short.Internal which uses ccall):

{-# LANGUAGE MagicHash #-}
{-# LANGUAGE CApiFFI #-}
{-# LANGUAGE UnliftedFFITypes #-}

foreign import capi unsafe "string.h memcmp"
  c_memcmp_ByteArray :: ByteArray# -> ByteArray# -> CSize -> IO CInt

assigned to @trac-igloo

Igloo, you are the man who implemented the CApi stuff. Might you look into this?

Simon

removed milestone

Moving to 7.12.1 milestone; if you feel this is an error and should be addressed sooner, please move it back to the 7.10.1 milestone.

changed milestone to %8.0.1

Milestone renamed

changed milestone to %8.2.2

changed weight to 7

Trac metadata

Trac field	Value
Priority	normal → high

mentioned in commit add85cc2

added 1 deleted label

closed

Merged to ghc-8.2 in 95c1feeb.

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

removed 1 deleted label

mentioned in issue #14624 (closed)

added compiler crash label

added Phigh label

mentioned in commit 9bcc7f53

mentioned in merge request !8483 (closed)

mentioned in commit 130f67db

mentioned in commit 003489a0

mentioned in commit 7d92cf3e

mentioned in commit d6f4f0c9

mentioned in commit bf2c2c35

mentioned in commit 49be12fd

mentioned in commit d0722170

mentioned in issue #22705