[GHC] #11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ $ ghc-head --info | grep Project [("Project name","The Glorious Glasgow Haskell Compilation System") ,("Project version","8.1.20151231") ,("Project Git commit id","8afeaad919dc67643b4eff14efafb48b59039b2b") }}} {{{ $ make slowtest TEST=tc198 TEST_HC=ghc-head VERBOSE=2 =====> tc198(normal) 1 of 1 [0, 0, 0] =====> tc198(hpc) 1 of 1 [0, 0, 0] Compile failed (status 256) errors were: ghc: panic! (the 'impossible' happened) (GHC version 8.1.20151231 for x86_64-unknown-linux): lookupVers2 GHC.Stack.Types CallStack Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *** unexpected failure for tc198(hpc) =====> tc198(optasm) 1 of 1 [0, 1, 0] Compile failed (status 256) errors were: ghc: panic! (the 'impossible' happened) (GHC version 8.1.20151231 for x86_64-unknown-linux): lookupVers2 GHC.Stack.Types CallStack Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug *** unexpected failure for tc198(optasm) Unexpected results from: TEST="tc198" }}} Test was added in 2005. Seems like a release blocker. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by gridaphobe): * owner: => gridaphobe Comment: Thanks, I'm out of town this week but will investigate when I get back! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): A couple initial observations: 1. The panic happens when ghc builds the ModIface, specifically when fingerprinting `GHC.Stack.Types.CallStack`. 2. The panic only occurs with `-O`. The module is so simple that the Core is unchanged by optimizations, but the optimized Core does include an unfolding that mentions the `CallStack` type. So, it looks like GHC is trying to fingerprint `CallStack` to write out the interface file, but fails because `GHC.Stack.Types` was never loaded. The question then is why did we not load `GHC.Stack.Types`? It's clearly imported by `GHC.Err`, the interface file confirms. But `-ddump-if-trace` doesn't mention `GHC.Stack.Types`.. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): I ran into this problem a few weeks ago. It seems that the place where `GHC.Stack.Types` normally gets loaded is the `dsLookupDataCon` call in `DsBinds.dsEvCallStack`. I found this peculiar at the time (why doesn't it get loaded earlier?) but the original source of the error (for me) was elsewhere. When I fixed that (to produce an `EvCallStack`), the problem went away. I don't know why this all is happening, but the knowledge that that particular call of `dsLookupDataCon` triggers loading in the successful case was a bit hard-won, so I thought I'd share. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): That actually makes a lot of sense, thanks! The CallStack tycon is wired- in, so the type-checker wouldn't have to load GHC.Types.Stack. The datacon is not, nor is the newer pushCallStack function we use in the desugarer, so that's why it would be loaded during desugaring. In this case we're not generating any CallStacks, so dsEvCallStack is not called, so the module is not loaded. Hrm.. What is the usual rule for loading modules that contain wired-in things? Or is it even necessary to fingerprint a wired-in thing? (By the way, how ''did'' you figure out what was triggering the load?) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Look at `Note [Loading instances for wired-in things]` in `LoadIface`. You should call `checkWiredInTyCon` when (but only when) you are using `CallStack` but not ''mentioning'' it. A classic example is when you write {{{ f :: [a] -> [a] }}} The explicit list syntax `[a]` uses `listTyCon` but does not mention it explicitly. Ditto tuples. Hence the calls to `checkWiredInTyCon` in `TcHsType`. Ah! I see what is happening. * `tc198` uses `undefined`, which is wired-in. * But the type of `undefined` mentions `CallStack`. * In `tcImportDecl_maybe`, we check for wired-in things, and call `loadWiredInHomeInterface` -- but only if `needWiredInHomeInterface` is True. * `needWiredInHomeInterace` is False of Ids; and even if it were True, we'd load `undefined`'s home interface not `CallStack`'s. The reason for the `loadWiredInHomeInterface` stuff is really to get `instance` declarations. And I suppose that if we have a wired-in Id whose type is `Bool -> M.T`, then we perhaps ought to check that `M.T`'s home interface is loaded in case there are any instances for it which we might need. So one solution is to adapt the wired-in-Id case of `tcImportDecl_maybe` to call `checkWiredInTyCon` on any `TyCon`s in the Id's type. But in fact the reason we need the home interface is ''not'' because of instances but to get its fingerprint. And it does seem bizarre to me that the fingerprint of a wired-in thing appears in the interface file if thing itself does not. Can't we give all wired-in things a fingerprint of zero? After all, they are wired-in. If we change them we change the compiler, and there are many cases in which changing the compiler requires a clean rebuild. In this case the worst that could happen would be some missing recompilation, and that is also an issue when, for example, we change interface file format. So I say that for wired-in things * make `MkIface.mkHashFun` return zero for wired-in names * filter out wired-in names when constructing fingerprints That would solve this ticket. Technically there is still a potential problem with missing instances (see above) but in practice it doesn't occur, and closing that theoretical hole would take more code and slow down every compilation. Any other observations/thoughts? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Replying to [comment:4 gridaphobe]:
(By the way, how ''did'' you figure out what was triggering the load?)
Erm... I used this brand new feature called implicit call stacks to trace back who was making the calls to load `GHC.Stack.Types` in the successful case. It's a bit odd how useful the feature was in debugging its own implementation. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): Thanks for the explanation Simon. I agree with your proposal re wired-in things, I'll send a patch. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: new Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): It looks like things are a bit more complicated than we thought. Judging by https://github.com/ghc/ghc/blob/master/compiler/iface/MkIface.hs#L219 and https://github.com/ghc/ghc/blob/master/compiler/iface/MkIface.hs#L425 ghc already filters out wired-in names during fingerprinting. In fact, the real problem is that the `GHC.Stack.Types.CallStack` Name that triggers the exception '''isn't''' wired-in, which is completely bogus. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: patch Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1739 Wiki Page: | -------------------------------------+------------------------------------- Changes (by gridaphobe): * status: new => patch * differential: => Phab:D1739 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: patch Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1739 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Ah yes, that patch looks right. Does it cure the problem? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: patch Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1739 Wiki Page: | -------------------------------------+------------------------------------- Comment (by gridaphobe): Yep, `make slowtest TEST=tc198` passes locally now. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: patch Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1739 Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): D1739 is currently blocked on goldfire, since we would like to unwire `error` and `undefined` to simplify this whole mess. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack
-------------------------------------+-------------------------------------
Reporter: thomie | Owner: gridaphobe
Type: bug | Status: patch
Priority: highest | Milestone: 8.0.1
Component: Compiler | Version: 7.11
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s): Phab:D1739
Wiki Page: |
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Comment (by Ben Gamari
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: merge Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1739 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: patch => merge -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
#11331: panic! TEST=tc198: lookupVers2 GHC.Stack.Types CallStack -------------------------------------+------------------------------------- Reporter: thomie | Owner: gridaphobe Type: bug | Status: closed Priority: highest | Milestone: 8.0.1 Component: Compiler | Version: 7.11 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1739 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: merge => closed * resolution: => fixed Comment: This was merged to `ghc-8.0` in b31aafb7064480055e067924e0ecfcf47e3082b0. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11331#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler
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