https://gitlab.haskell.org/ghc/ghc/-/issues/22282

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  * Glasgow Haskell CompilerGlasgow Haskell Compiler
  * GHCGHC
  * Issues
  * #22282

Closed
Open
Issue created Oct 11, 2022 by [gi]Jade Lovelace@lf-
 

GHC 9.4.2 regresses being able to do math on aarch64

  Summary

 

I found this test failure while working on nixpkgs on aarch64. This
is extremely alarming, before I reduced it to a simpler program using
only base, at which point I am out-of-this-world alarmed.

 

https://github.com/haskell-foundation/foundation/issues/571

 

  Steps to reproduce

 

Stick this in Main.hs:

 
 

{-# LANGUAGE NoImplicitPrelude, OverloadedStrings, RankNTypes, ScopedTypeVariables, NoRebindableSyntax #-}
module Main where

import Prelude
import System.Environment
import Data.Word

testF :: Word8 -> Word8 -> Bool
testF a b =
    if b == 0 then True
              else a == (a `div` b) * b + (a `mod` b)

main :: IO ()
main = do
    args <- getArgs
    let [a :: Word8, b] = read <$> args
    putStrLn . show $ testF a b

  
 

Then:

 
 

co/ghc942bug >> ghc -O1 app/Main.hs
[1 of 2] Compiling Main             ( app/Main.hs, app/Main.o )
[2 of 2] Linking app/Main

co/ghc942bug >> app/Main 217 161
False
co/ghc942bug >> ghc -O0 app/Main.hs
[1 of 2] Compiling Main             ( app/Main.hs, app/Main.o ) [Optimisation flags changed]
[2 of 2] Linking app/Main [Objects changed]

co/ghc942bug >> app/Main 217 161
True

  
 

Note that it's fine on 9.2.4:

 
 

co/ghc942bug >> ghcup set 9.2.4
[ Warn  ] This is an old-style command for setting GHC. Use 'ghcup set ghc' instead.
[ Info  ] GHC 9.2.4 successfully set as default version
co/ghc942bug >> ghc -O0 app/Main.hs
[1 of 1] Compiling Main             ( app/Main.hs, app/Main.o )
Linking app/Main ...
co/ghc942bug >> app/Main 217 161
True
co/ghc942bug >> ghc -O1 app/Main.hs
[1 of 1] Compiling Main             ( app/Main.hs, app/Main.o ) [Optimisation flags changed]
Linking app/Main ...
co/ghc942bug >> app/Main 217 161
True

  
 

On Linux, GHC 9.4.2 from nixpkgs (qemu on Apple Silicon):

 
 

~ >> ghc -O1 Repro.hs
[1 of 2] Compiling Main             ( Repro.hs, Repro.o )
[2 of 2] Linking Repro
~ >> ./Repro 217 161
False
~ >> ghc -O0 Repro.hs
[1 of 2] Compiling Main             ( Repro.hs, Repro.o ) [Optimisation flags changed]
[2 of 2] Linking Repro [Objects changed]
~ >> ./Repro 217 161
True
~ >> uname -a
Linux thinnix 5.15.47 #1-NixOS SMP Tue Jun 14 16:36:28 UTC 2022 aarch64 GNU/Linux

  
 

  Expected behavior

 

It should return True in both optimization configurations.

 

  Environment

 

     
  * GHC version used: 9.4.2 from ghcup although it also happens on
    ghc from nix. It's fine in ghc 9.2.4. 

 

Optional:

 

     
  * Operating System: macOS, although it also happens on
    aarch64-linux 
  * System Architecture: aarch64 

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