#13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: Compiler | Version: 8.0.2-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | 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 RyanGlScott): Here's a minimized version with no dependencies: {{{#!hs {-# LANGUAGE BangPatterns #-} module Bug (foo, bar) where import Data.IORef (IORef, newIORef, readIORef, writeIORef) import System.IO.Unsafe (unsafePerformIO) {-# NOINLINE scServerState #-} scServerState :: SCServerState scServerState = unsafePerformIO (return undefined) data SCServerState = SCServerState { scServer_socket :: IORef (Maybe Int) } foo :: IO Int foo = do let !_ = scServerState readIORef (scServer_socket scServerState) >>= \xs -> case xs of Nothing -> do s <- undefined writeIORef (scServer_socket scServerState) (Just s) return s Just s -> return s bar :: IO () bar = do let !_ = scServerState return () }}} You can get this error message with GHC 8.0.1, 8.0.2, or HEAD: {{{ $ /opt/ghc/8.0.1/bin/ghc -fforce-recomp -O1 Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) /tmp/ghc654_0/ghc_2.s: Assembler messages: /tmp/ghc654_0/ghc_2.s:562:0: error: Error: symbol `Bug_scServerState_closure' is already defined `gcc' failed in phase `Assembler'. (Exit code: 1) }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13043#comment:1> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: Compiler | Version: 8.0.2-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | 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 RyanGlScott): * cc: simonpj (added) Comment: Simon's commit 649cb346a38684df2e932987065817c5cafc2d90 is responsible for this regression. Reid, do you know which ticket this is a dupe of? If so, I'll close this in favor of that one. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13043#comment:3> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: Compiler | Version: 8.0.2-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #12595 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): I did a bit of digging into what is happening here: early in simplification we have the core, {{{#!hs scServerState [InlPrag=NOINLINE] :: SCServerState scServerState = ... foo_s1Sx :: State# RealWorld -> (# State# RealWorld, Int #) foo_s1Sx = \ (eta_B1 [OS=OneShot] :: State# RealWorld) -> case case scServerState of _ [InlPrag=NOINLINE, Occ=Dead] { SCServerState ipv_s1S8 -> GHC.Tuple.() } of _ [Occ=Dead] { () -> ... }}} Eventually case-of-case (and perhaps something else) fires, giving us, {{{#!hs foo_s1Sx = \ (eta_B1 [OS=OneShot] :: State# GHC.Prim.RealWorld) -> case scServerState of scServerState [InlPrag=NOINLINE] { SCServerState ipv_s1S8 -> case scServerState of _ [Occ=Dead] { SCServerState ds_d1Qj -> ... }}} Note that we are now shadowing the `scServerState` binder. This already seems suspicious. This then gets transformed to a `let` by the lifted case elimination simplification (see `Note [Case elimination: lifted case]`), {{{#!hs -- from phase foo_s1Sx = \ (eta_B1 [Dmd=<S,U>, OS=OneShot] :: State# GHC.Prim.RealWorld) -> let { scServerState [InlPrag=NOINLINE, Dmd=<S(S(S)),1*U(1*U(U))>] :: SCServerState [LclId, Str=DmdType, Unf=Unf{Src=<vanilla>, TopLvl=False, Value=False, ConLike=False, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=0,unsat_ok=True,boring_ok=True)}] scServerState = scServerState } in case scServerState of _ [Occ=Dead, Dmd=<L,A>] { SCServerState ds_d1Qj [Dmd=<S(S),1*U(U)>] -> ... }}} The let-bound `scServerState` is then floated to the top-level, resulting in the duplicate closures we see here. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13043#comment:5> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.3 Component: Compiler | Version: 8.0.2-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #12595 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones <simonpj@…>): In [changeset:"baf9ebe55a51827c0511b3a670e60b9bb3617ab5/ghc" baf9ebe5/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="baf9ebe55a51827c0511b3a670e60b9bb3617ab5" Ensure nested binders have Internal Names This is a long-standing bug. A nested (non-top-level) binder in Core should not have an External Name, like M.x. But - Lint was not checking this invariant - The desugarer could generate programs that failed the invariant. An example is in tests/deSugar/should_compile/T13043, which had let !_ = M.scState in ... This desugared to let ds = case M.scSate of M.scState { DEFAULT -> () } in case ds of () -> ... We were wrongly re-using that scrutinee as a case binder. And Trac #13043 showed that could ultimately lead to two top-level bindings with the same closure name. Alas! - The desugarer had one other place (in DsUtils.mkCoreAppDs) that could generate bogus code This patch fixes all three bugs, and adds a regression test. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13043#comment:7> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

#13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures -------------------------------------+------------------------------------- Reporter: hvr | Owner: Type: bug | Status: merge Priority: normal | Milestone: 8.0.3 Component: Compiler | Version: 8.0.2-rc2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #12595 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): PS thank you for a nice repro case -- made it far easier to find. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13043#comment:9> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler