#15108: Panic: collectNBinders -------------------------------------+------------------------------------- Reporter: cdisselkoen | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Profiling | Version: 8.4.2 Resolution: | Keywords: panic | collectNBinders Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by cdisselkoen: Old description:

GHC 8.4.2 panics with the error message `collectNBinders`, when compiling with profiling. This is a very similar bug to #15002, but although #15002 is fixed in 8.4.2, this panic persists.

Steps to reproduce:

`stack.yaml`: {{{ resolver: nightly-2018-04-30 }}}

`bug.cabal`: {{{ name: bug version: 0.1.0.0 build-type: Simple cabal-version: >=1.10

library build-depends: base default-language: Haskell2010

executable bug main-is: Main.hs build-depends: base , bug default-language: Haskell2010 }}}

`Main.hs`: {{{ module Main where

main :: IO () main = do _ <- return $ getInt Circle return ()

newtype MyInt = MyInt Int

data Shape = Circle | Square

getInt :: Shape -> MyInt getInt sh = case sh of Circle -> let (MyInt i) = MyInt 3 in myInt i Square -> let (MyInt i) = MyInt 2 in myInt i where myInt = MyInt }}}

Then run: {{{ $ stack ghc -- --version The Glorious Glasgow Haskell Compilation System, version 8.4.2

$ stack build --profile bug-0.1.0.0: build (lib + exe) Preprocessing library for bug-0.1.0.0.. Building library for bug-0.1.0.0.. Preprocessing executable 'bug' for bug-0.1.0.0.. Building executable 'bug' for bug-0.1.0.0.. [1 of 1] Compiling Main ( Main.hs, .stack-work/dist/x86_64 -linux-tinfo6-nopie/Cabal-2.2.0.1/build/bug/bug-tmp/Main.p_o ) ghc: panic! (the 'impossible' happened) (GHC version 8.4.2 for x86_64-unknown-linux): collectNBinders 1 Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/coreSyn/CoreSyn.hs:2025:25 in ghc:CoreSyn

Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug

-- While building custom Setup.hs for package bug-0.1.0.0 using: /usr/local/home/<USER>/.stack/setup-exe-cache/x86_64-linux- tinfo6-nopie/Cabal-simple_mPHDZzAJ_2.2.0.1_ghc-8.4.2 --builddir=.stack- work/dist/x86_64-linux-tinfo6-nopie/Cabal-2.2.0.1 build lib:bug exe:bug --ghc-options " -ddump-hi -ddump-to-file -fdiagnostics-color=always" Process exited with code: ExitFailure 1 }}}

New description: GHC 8.4.2 panics with the error message `collectNBinders`, when compiling with profiling. This is a very similar bug to #15002, but although #15002 is fixed in 8.4.2, this panic persists. Steps to reproduce: `stack.yaml`: {{{ resolver: nightly-2018-04-30 }}} `bug.cabal`: {{{ name: bug version: 0.1.0.0 build-type: Simple cabal-version: >=1.10 executable bug main-is: Main.hs build-depends: base default-language: Haskell2010 }}} `Main.hs`: {{{ module Main where main :: IO () main = do _ <- return $ getInt Circle return () newtype MyInt = MyInt Int data Shape = Circle | Square getInt :: Shape -> MyInt getInt sh = case sh of Circle -> let (MyInt i) = MyInt 3 in myInt i Square -> let (MyInt i) = MyInt 2 in myInt i where myInt = MyInt }}} Then run: {{{ $ stack ghc -- --version The Glorious Glasgow Haskell Compilation System, version 8.4.2 $ stack build --profile bug-0.1.0.0: build (lib + exe) Preprocessing library for bug-0.1.0.0.. Building library for bug-0.1.0.0.. Preprocessing executable 'bug' for bug-0.1.0.0.. Building executable 'bug' for bug-0.1.0.0.. [1 of 1] Compiling Main ( Main.hs, .stack-work/dist/x86_64 -linux-tinfo6-nopie/Cabal-2.2.0.1/build/bug/bug-tmp/Main.p_o ) ghc: panic! (the 'impossible' happened) (GHC version 8.4.2 for x86_64-unknown-linux): collectNBinders 1 Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/coreSyn/CoreSyn.hs:2025:25 in ghc:CoreSyn Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- While building custom Setup.hs for package bug-0.1.0.0 using: /usr/local/home/<USER>/.stack/setup-exe-cache/x86_64-linux- tinfo6-nopie/Cabal-simple_mPHDZzAJ_2.2.0.1_ghc-8.4.2 --builddir=.stack- work/dist/x86_64-linux-tinfo6-nopie/Cabal-2.2.0.1 build lib:bug exe:bug --ghc-options " -ddump-hi -ddump-to-file -fdiagnostics-color=always" Process exited with code: ExitFailure 1 }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15108#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15108: Panic: collectNBinders -------------------------------------+------------------------------------- Reporter: cdisselkoen | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Profiling | Version: 8.4.2 Resolution: | Keywords: panic | collectNBinders Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by cdisselkoen): Note: also reproduces with GHC 8.2.2 (stackage `lts-11.7`). {{{ $ stack ghc -- --version The Glorious Glasgow Haskell Compilation System, version 8.2.2 $ stack build --profile bug-0.1.0.0: configure (exe) Configuring bug-0.1.0.0... bug-0.1.0.0: build (exe) Preprocessing executable 'bug' for bug-0.1.0.0.. Building executable 'bug' for bug-0.1.0.0.. [1 of 1] Compiling Main ( Main.hs, .stack-work/dist/x86_64 -linux-tinfo6-nopie/Cabal-2.0.1.0/build/bug/bug-tmp/Main.p_o ) ghc: panic! (the 'impossible' happened) (GHC version 8.2.2 for x86_64-unknown-linux): collectNBinders 1 Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/coreSyn/CoreSyn.hs:1997:25 in ghc:CoreSyn Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- While building custom Setup.hs for package bug-0.1.0.0 using: /usr/local/home/cdisselk/.stack/setup-exe-cache/x86_64-linux- tinfo6-nopie/Cabal-simple_mPHDZzAJ_2.0.1.0_ghc-8.2.2 --builddir=.stack- work/dist/x86_64-linux-tinfo6-nopie/Cabal-2.0.1.0 build exe:bug --ghc- options " -ddump-hi -ddump-to-file -fdiagnostics-color=always" Process exited with code: ExitFailure 1 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15108#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15108: Panic: collectNBinders -------------------------------------+------------------------------------- Reporter: cdisselkoen | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Profiling | Version: 8.4.2 Resolution: | Keywords: panic | collectNBinders Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by nomeata): Thanks for the nice test case, I added it to the test suite. JFTR, this can be easily reproduced without stack or GHC: {{{ ~/build/haskell/ghc-master $ ./inplace/bin/ghc-stage2 testsuite/tests/profiling/should_compile/T15108.hs -prof -fprof-auto -dcore-lint [1 of 1] Compiling Main ( testsuite/tests/profiling/should_compile/T15108.hs, testsuite/tests/profiling/should_compile/T15108.o ) *** Core Lint errors : in result of Desugar (after optimization) *** testsuite/tests/profiling/should_compile/T15108.hs:22:7: warning: [RHS of myInt_aVZ :: Int -> MyInt] Join point has too few lambdas Join var: myInt_aVZ Join arity: 1 Number of lambdas: 0 Rhs = scctick MyInt *** Offending Program *** getInt :: Shape -> MyInt [LclIdX] getIntghc-stage2: panic! (the 'impossible' happened) (GHC version 8.5.20180410 for x86_64-unknown-linux): collectNBinders 1 Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1162:37 in ghc:Outputable pprPanic, called at compiler/coreSyn/CoreSyn.hs:2056:25 in ghc:CoreSyn Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} As you can see, it does not require any optimization level, and the bug is in place right after the desugarer. Maybe the optimizer copies the join arity from `MyInt` to `myInt`, under the assumption that `myInt` will be inlined, but the `scctick` prevents that from happening? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15108#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15108: Panic: collectNBinders -------------------------------------+------------------------------------- Reporter: cdisselkoen | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Profiling | Version: 8.4.2 Resolution: | Keywords: panic | collectNBinders Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"07cc6039dccff82790bf1d84a81e26df234ad899/ghc" 07cc603/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="07cc6039dccff82790bf1d84a81e26df234ad899" Don't crash when pretty-printing bad joins Trac #15108 showed that the Core pretty-printer would crash if it found a join-point binding with too few lambda on the RHS. That is super-unhelpful! Lint will find it, but pretty-printing should not crash. This patch just makes the pretty printer behave more robustly; it leaves the job of error reporting to Lint. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15108#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15108: Panic: collectNBinders -------------------------------------+------------------------------------- Reporter: cdisselkoen | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Profiling | Version: 8.4.2 Resolution: fixed | Keywords: panic | collectNBinders Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * resolution: => fixed * milestone: => 8.6.1 Comment: OK, fixed. Thanks for a great report. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15108#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#15108: Panic: collectNBinders -------------------------------------+------------------------------------- Reporter: cdisselkoen | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Profiling | Version: 8.4.2 Resolution: fixed | Keywords: panic | collectNBinders Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I suppose we could, but a key aspect of the current join points is that their semantics is exactly that of let-bindings; and often code (e.g. strictness analysis) can work uniformly for both. Yes, there are many ways in which we could change the representation. E.g. maybe `Lam` should take a list of binders, or `App` should take a list of arguments. But my instinct is that you save code in some places and lose it in others. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15108#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler