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

31 Jan 2019

      #16258: PowerPC Big-Endian: ArithInt16, ArithInt8, ArithWord16, and ArithWord8 fail
-------------------------------------+-------------------------------------
        Reporter:  trommler          |                Owner:  trommler
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.10.1
       Component:  Compiler          |              Version:  8.7
      Resolution:                    |             Keywords:  Big-endian
Operating System:  Unknown/Multiple  |         Architecture:  powerpc64
 Type of failure:  Incorrect result  |            Test Case:
  at runtime                         |  primops/should_run/ArithInt16,
                                     |  primops/should_run/ArithWord16,
                                     |  primops/should_run/ArithWord8,
                                     |  primops/should_run/ArithInt8
      Blocked By:                    |             Blocking:
 Related Tickets:  #16222            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by trommler:

Old description:
...
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.
New description:

 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 bug is different from #16222, which deals with the C calling
 convention.

--

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16258#comment:2
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