dsrun014 fails with most ways

The dsrun014 test doesn't seem to pass for a whole bunch of ways, as a recent ./validate --slow (against yesterday's master) revealed.

# the test options
test('dsrun014', normal, compile_and_run, ['-fobject-code'])

-- the haskell program we build & run
{-# LANGUAGE UnboxedTuples #-}

module Main where

import Debug.Trace

{-# NOINLINE f #-}
f :: a -> b -> (# a,b #)
f x y = x `seq` y `seq` (# x,y #)

g :: Int -> Int -> Int
g v w = case f v w of
          (# a,b #) -> a+b

main = print (g (trace "one" 1) (trace "two" 2))
-- The args should be evaluated in the right order!

# the failing ways
/tmp/ghctest-n4fi8zlk/test   spaces/./deSugar/should_run/dsrun014.run            dsrun014 [bad stderr] (hpc)
/tmp/ghctest-n4fi8zlk/test   spaces/./deSugar/should_run/dsrun014.run            dsrun014 [bad stderr] (optasm)
/tmp/ghctest-n4fi8zlk/test   spaces/./deSugar/should_run/dsrun014.run            dsrun014 [bad stderr] (threaded2)
/tmp/ghctest-n4fi8zlk/test   spaces/./deSugar/should_run/dsrun014.run            dsrun014 [bad stderr] (dyn)
/tmp/ghctest-n4fi8zlk/test   spaces/./deSugar/should_run/dsrun014.run            dsrun014 [bad stderr] (optllvm)

With those 5 ways, the program's trace is two then one while with some other ways (like ghci or normal) we get (as expected by the testsuite) one first and two afterwards.

I'm not sure whether the expectation is too strong or whether there's something fishy going on with those 5 ways.

Simon, could you perhaps comment on this? Is this a "proper" bug?

changed weight to 5

added Tbug Trac import labels

This test was apparently added for #1031 (closed).

If I change one or more seqs into pseq, in order for this test to be a little more useful (because pseq might prevent some transformations that could make things go wrong with seq, so we can hope that the trace is reliably one then two), ghc isn't happy:

...
import GHC.Conc
...

{-# NOINLINE f #-}
f :: a -> b -> (# a,b #)
f x y = x `pseq` y `pseq` (# x,y #)
-- similar with x `pseq` y `seq` (# x,y #)

dsrun014.hs:10:9: error:
    • Couldn't match a lifted type with an unlifted type
      When matching types
        b0 :: *
        (# a, b #) :: TYPE
                        ('GHC.Types.TupleRep '['GHC.Types.LiftedRep, 'GHC.Types.LiftedRep])
    • In the expression: x `pseq` y `pseq` (# x, y #)
      In an equation for ‘f’: f x y = x `pseq` y `pseq` (# x, y #)
    • Relevant bindings include
        y :: b (bound at dsrun014.hs:10:5)
        x :: a (bound at dsrun014.hs:10:3)
        f :: a -> b -> (# a, b #) (bound at dsrun014.hs:10:1)

dsrun014.hs:10:27: error:
    • Couldn't match a lifted type with an unlifted type
      When matching types
        b0 :: *
        (# a, b #) :: TYPE
                        ('GHC.Types.TupleRep '['GHC.Types.LiftedRep, 'GHC.Types.LiftedRep])
    • In the second argument of ‘pseq’, namely ‘(# x, y #)’
      In the second argument of ‘pseq’, namely ‘y `pseq` (# x, y #)’
      In the expression: x `pseq` y `pseq` (# x, y #)
    • Relevant bindings include
        y :: b (bound at dsrun014.hs:10:5)
        x :: a (bound at dsrun014.hs:10:3)

changed title from dsrun004 fails with most ways to dsrun014 fails with most ways

changed the description

Trac metadata

Trac field	Value
Test case	dsrun004 → dsrun014

alpmestan, this is a consequence of the fact that seq has special typing rules. See Note [Typing rule for seq] in http://git.haskell.org/ghc.git/blob/efc844f5b955385d69d8e20b80d38311083a6665:/compiler/typecheck/TcExpr.hs#l334 how this is implemented (and why it's special).

pseq does not have corresponding special typing rules, which is why it fails when given an unlifted argument. Should pseq be given similar magic? I'm not sure.

I tried to extend that code to do the same thing for pseq but it looks like that did not quite work (see this gist). I'm probably missing something obvious here though.

Oh, well I can't just expect GHC to magically use that "id" can I... I'll look at how the mapping is done for seq and then do the same thing for pseq.

added incorrect runtime result label

added broken test label

added Pnormal label

mentioned in commit 6e1bc8c2

mentioned in commit 4ef98eeb

mentioned in commit 00f7e0e6