Program with safe array operations triggers debug runtime assertion

I'll try to minimize later.

Main.hs:

{-# LANGUAGE ForeignFunctionInterface #-}
import Control.Monad
import Control.Monad.ST
import Data.Primitive.Array
import Data.Primitive.ByteArray
import Data.Primitive.SmallArray
import System.Environment
import System.Mem
import Foreign.C

data A arr = A !Int arr

enumSmallArray :: Int -> A (SmallArray Int)
enumSmallArray n = runST $ do
  arr <- newSmallArray n 0
  forM_ [1..n] $ \i ->
    writeSmallArray arr i i
  iarr <- freezeSmallArray arr 0 n
  return (A n iarr)

consumeSmallArray :: A (SmallArray a) -> a
consumeSmallArray (A n arr) = indexSmallArray arr (n - 1)

enumArray :: Int -> A (Array Int)
enumArray n = runST $ do
  arr <- newArray n 0
  forM_ [1..n] $ \i ->
    writeArray arr i i
  iarr <- freezeArray arr 0 n
  return (A n iarr)

consumeArray :: A (Array a) -> a
consumeArray (A n arr) = indexArray arr (n - 1)

foreign import ccall "printInt"
  printInt :: CInt -> IO ()

main :: IO ()
main = do
  n <- (\[s] -> read s) <$> getArgs
  ints <- forM [1..n] $ \i -> do
    let x = consumeSmallArray (enumSmallArray 12)
        y = consumeArray (enumArray i)
    case x+y of
      r -> when (i `mod` 5000 == 0) performMajorGC
        >> return r
  printInt (fromIntegral (sum ints))

print.c:

#include <stdio.h>

void printInt(int i) { printf("Result: %d\n", i); }

Compile:

$ ghc Main.hs print.c -debug
Linking Main ...

Run:

array_bug $ ./Main 1000 +RTS -DS
Main: internal error: ASSERTION FAILED: file rts/sm/Storage.c, line 960

    (GHC version 8.6.1 for x86_64_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
zsh: abort (core dumped)  ./Main 1000 +RTS -DS

Tried with: 8.4.3, 8.6.1.

Trac metadata

Trac field	Value
Version	8.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Runtime System
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	bgamari
Operating system
Architecture