(Simon Marlow, can you help?) I don't understand how breakpoints work. Why do you say "we are clearly trying to float past a breakpoint"? Why is it so clear? Why is it wrong to float a lazy thunk out of a breakpoint? The float-out pass really doesn't have anywhere else where we say "you really can't float anything out of this subexpression, not even top-level constant expressions". Simon | -----Original Message----- | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Peter | Wortmann | Sent: 04 February 2015 17:24 | To: ghc-devs@haskell.org | Subject: Re: [GHC] #10052: Panic (something to do with floatExpr?) | | | | We are clearly trying to float past a breakpoint here, which is simply | impossible. Pretty sure this would have been a panic before my changes | too (it would have tried to "mkNoCount" the breakpoint). Guess I was | wrong reading a "breakpoints don't appear here" invariant out of that... | | The quick fix would be to drop all floats in-place: | | -- scoped, counting and unsplittable, can't be floated through | | otherwise | = floatBody tOP_LEVEL expr | | This fixes the panic, but is a bit awkward. Probably better to change | SetLevels? Not a piece of code I'm very familiar with... | | Greetings, | Peter | | On 04/02/2015 13:31, Simon Peyton Jones wrote: | > Peter: | > | > Here's a bad crash, due to you. (Doing this by email because I'm | offline.) | > | > The (Tick t e) case of FloatOut.floatExpr is incomplete. It simply | panics in some cases. | > | > Could you fix this please? Either that case shouldn't happen, in which | case Core Lint should check for it, and whoever is generating it should | be fixed. Or it should happen, in which case floatExpr should do the | right thing. | > | > Could you leave a Note to explain what is happening in the floatExpr | (Tick ...) cases? | > | > Thanks | > | > Simon | > | > | -----Original Message----- | > | From: ghc-tickets [mailto:ghc-tickets-bounces@haskell.org] On Behalf | Of | > | GHC | > | Sent: 31 January 2015 17:38 | > | Cc: ghc-tickets@haskell.org | > | Subject: [GHC] #10052: Panic (something to do with floatExpr?) | > | | > | #10052: Panic (something to do with floatExpr?) | > | -------------------------------------+------------------------------- | ---- | > | -- | > | Reporter: edsko | Owner: | > | Type: bug | Status: new | > | Priority: normal | Milestone: | > | Component: Compiler | Version: 7.10.1-rc2 | > | Keywords: | Operating System: | > | Unknown/Multiple | > | Architecture: | Type of failure: | None/Unknown | > | Unknown/Multiple | Blocked By: | > | Test Case: | Related Tickets: | > | Blocking: | | > | Differential Revisions: | | > | -------------------------------------+------------------------------- | ---- | > | -- | > | Loading | > | | > | {{{ | > | main = let (x :: String) = "hello" in putStrLn x | > | }}} | > | | > | using a very simple driver for the GHC API (see T145.hs) causes a | ghc | > | panic: | > | | > | {{{ | > | [1 of 1] Compiling Main ( T145-input.hs, interpreted ) | > | T145: T145: panic! (the 'impossible' happened) | > | (GHC version 7.10.0.20150128 for x86_64-apple-darwin): | > | floatExpr tick | > | <<details unavailable>> | > | | > | Please report this as a GHC bug: | http://www.haskell.org/ghc/reportabug | > | }}} | > | | > | This panic is arising in our test case for #8333, so it may be | related | > | to | > | that bug. | > | | > | -- | > | Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10052 | > | GHC http://www.haskell.org/ghc/ | > | The Glasgow Haskell Compiler | > | _______________________________________________ | > | ghc-tickets mailing list | > | ghc-tickets@haskell.org | > | http://www.haskell.org/mailman/listinfo/ghc-tickets | > | | _______________________________________________ | ghc-devs mailing list | ghc-devs@haskell.org | http://www.haskell.org/mailman/listinfo/ghc-devs

Peter, OK. This is really beyond my knowledge. Might you and Simon be able to work out something together? I can advise on FloatOut if necessary. Simon | -----Original Message----- | From: Peter Wortmann [mailto:scpmw@leeds.ac.uk] | Sent: 05 February 2015 11:47 | To: Simon Peyton Jones; Simon Marlow | Cc: ghc-devs@haskell.org | Subject: Re: [GHC] #10052: Panic (something to do with floatExpr?) | | | | Simon Peyton Jones wrote: | > Why do you say "we are clearly trying to float past a breakpoint"? Why | is it so clear? | | It's the only kind of Tickish that is scoped, counting and not | splittable. | | This means that we can't | | a) Simply float code out of it, because the payload must still be | covered (scoped) | | b) Copy the tick, because it would change entry counts (here: duplicate | breakpoints) | | > Why is it wrong to float a lazy thunk out of a breakpoint? | | Good questions - I haven't given breakpoint semantics a lot of thought, | to be honest. My assumption was that most optimisation passes would | never see them. And where they did, they should just leave them in peace | as much as possible. | | For whatever it's worth, the source cautions against making breakpoints | unscoped: | | -- Breakpoints are scoped: eventually we're going to do call | -- stacks, but also this helps prevent the simplifier from moving | -- breakpoints around and changing their result type (see #1531). | | Hm. We might try to make them pseudo-splittable, with non-counting | breakpoints being NOPs for now? This might still allow us to implement | breakpoint-based stack traces if we really want them... | | Greetings, | Peter | | > Simon | > | > | -----Original Message----- | > | From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of | Peter | > | Wortmann | > | Sent: 04 February 2015 17:24 | > | To: ghc-devs@haskell.org | > | Subject: Re: [GHC] #10052: Panic (something to do with floatExpr?) | > | | > | | > | | > | We are clearly trying to float past a breakpoint here, which is | simply | > | impossible. Pretty sure this would have been a panic before my | changes | > | too (it would have tried to "mkNoCount" the breakpoint). Guess I was | > | wrong reading a "breakpoints don't appear here" invariant out of | that... | > | | > | The quick fix would be to drop all floats in-place: | > | | > | -- scoped, counting and unsplittable, can't be floated through | > | | otherwise | > | = floatBody tOP_LEVEL expr | > | | > | This fixes the panic, but is a bit awkward. Probably better to change | > | SetLevels? Not a piece of code I'm very familiar with... | > | | > | Greetings, | > | Peter | > | | > | On 04/02/2015 13:31, Simon Peyton Jones wrote: | > | > Peter: | > | > | > | > Here's a bad crash, due to you. (Doing this by email because I'm | > | offline.) | > | > | > | > The (Tick t e) case of FloatOut.floatExpr is incomplete. It simply | > | panics in some cases. | > | > | > | > Could you fix this please? Either that case shouldn't happen, in | which | > | case Core Lint should check for it, and whoever is generating it | should | > | be fixed. Or it should happen, in which case floatExpr should do the | > | right thing. | > | > | > | > Could you leave a Note to explain what is happening in the | floatExpr | > | (Tick ...) cases? | > | > | > | > Thanks | > | > | > | > Simon | > | > | > | > | -----Original Message----- | > | > | From: ghc-tickets [mailto:ghc-tickets-bounces@haskell.org] On | Behalf | > | Of | > | > | GHC | > | > | Sent: 31 January 2015 17:38 | > | > | Cc: ghc-tickets@haskell.org | > | > | Subject: [GHC] #10052: Panic (something to do with floatExpr?) | > | > | | > | > | #10052: Panic (something to do with floatExpr?) | > | > | -------------------------------------+--------------------------- | ---- | > | ---- | > | > | -- | > | > | Reporter: edsko | Owner: | > | > | Type: bug | Status: new | > | > | Priority: normal | Milestone: | > | > | Component: Compiler | Version: | 7.10.1-rc2 | > | > | Keywords: | Operating System: | > | > | Unknown/Multiple | > | > | Architecture: | Type of failure: | > | None/Unknown | > | > | Unknown/Multiple | Blocked By: | > | > | Test Case: | Related Tickets: | > | > | Blocking: | | > | > | Differential Revisions: | | > | > | -------------------------------------+--------------------------- | ---- | > | ---- | > | > | -- | > | > | Loading | > | > | | > | > | {{{ | > | > | main = let (x :: String) = "hello" in putStrLn x | > | > | }}} | > | > | | > | > | using a very simple driver for the GHC API (see T145.hs) causes | a | > | ghc | > | > | panic: | > | > | | > | > | {{{ | > | > | [1 of 1] Compiling Main ( T145-input.hs, interpreted | ) | > | > | T145: T145: panic! (the 'impossible' happened) | > | > | (GHC version 7.10.0.20150128 for x86_64-apple-darwin): | > | > | floatExpr tick | > | > | <<details unavailable>> | > | > | | > | > | Please report this as a GHC bug: | > | http://www.haskell.org/ghc/reportabug | > | > | }}} | > | > | | > | > | This panic is arising in our test case for #8333, so it may be | > | related | > | > | to | > | > | that bug. | > | > | | > | > | -- | > | > | Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10052 | > | > | GHC http://www.haskell.org/ghc/ | > | > | The Glasgow Haskell Compiler | > | > | _______________________________________________ | > | > | ghc-tickets mailing list | > | > | ghc-tickets@haskell.org | > | > | http://www.haskell.org/mailman/listinfo/ghc-tickets | > | > | > | | > | _______________________________________________ | > | ghc-devs mailing list | > | ghc-devs@haskell.org | > | http://www.haskell.org/mailman/listinfo/ghc-devs