[GHC] #16258: PowerPC Big-Endian: ArithInt16, ArithInt8, ArithWord16, and ArithWord8 fail

30 Jan 2019

      #16258: PowerPC Big-Endian: ArithInt16, ArithInt8, ArithWord16, and ArithWord8 fail
-------------------------------------+-------------------------------------
           Reporter:  trommler       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.10.1
          Component:  Compiler       |           Version:  8.7
           Keywords:  Big-endian     |  Operating System:  Unknown/Multiple
       Architecture:  powerpc64      |   Type of failure:  Incorrect result
          Test Case:                 |  at runtime
  primops/should_run/ArithInt16,     |        Blocked By:
  primops/should_run/ArithWord16,    |
  primops/should_run/ArithWord8,     |
  primops/should_run/ArithInt8       |
           Blocking:                 |   Related Tickets:  #16222
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 The tests were run on a PowerMac G5 running Linux, PowerMacs are big-
 endian.

 I reduced the issue to this program where I get the incorrect answer
 `25132`:
 {{{#!hs
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE MagicHash #-}
 {-# LANGUAGE UnboxedTuples #-}

 module Main where

 import GHC.Exts

 main :: IO ()
 main = do
     putStrLn $ show (apply2 plusInt16# (50) (50))

 apply2 :: (Int16# -> Int16# -> Int16#) -> Int -> Int -> Int
 apply2 op (I# a) (I# b) =
     let (# sa, sb #) = (# narrowInt16# a, narrowInt16# b #)
         r = op sa sb
     in I# (extendInt16# r)
 {-# NOINLINE apply2 #-}
 }}}

 Curiously, when I inline `plusInt16#` and remove the op parameter the
 result is correct.

 The test passes on little-endian PowerPC 64-bit.

 Note: This is bug is different form #16222 that deals with the C calling
 convention.

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16258
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