bundle panic

[Jan Stolarek]

I don't see any commit fixing this so I assume that this is still relevant.

> Perhaps this is a problem that only shows up with proc points, which is
> why you wouldn't see it on x86_64/Linux. 
Wouldn't this also break some of Mac builds? Besides, my change was commited a few weeks ago, 
while Simon says this didn't happen a few days before.

> But Jan’s new optimisation to the stack overflow check (Note [Always false stack check] in
> CmmLayoutStack) ends up dropping a conditional branch, 
In theory my optimisation should not affect elimination of unnecessary branches in any way - this 
optimisation was there before. Note also that the last thing we do in Cmm pipeline is call to 
removeUnreachableBlocksProc so any unreachable block should be eliminated from the final graph - 
bundle is called later.

>so a call to gc is eliminated
A random guess: https://github.com/ghc/ghc/commit/ad0b943293cce74baf06ea36e1a4d51a3631dfdf
This was commited two days before you reported the problem and is GC-related.

Janek

Dnia niedziela, 17 listopada 2013, Simon Marlow napisał:
> On 16/11/13 00:16, Simon Peyton-Jones wrote:
> > I’ve looked into this myself.  I don’t think it’s actually anything
> > wrong in gmp-wrappers.  It’s because CmmBuildInfoTables expects all the
> > info tables in the (CmmProc info_tbls lbl g) to be defined in the graph
> > g.
> >
> > But Jan’s new optimisation to the stack overflow check (Note [Always
> > false stack check] in CmmLayoutStack) ends up dropping a conditional
> > branch, so a call to gc is eliminated, and hence a proc point is
> > eliminated, and we end up with an unused thing in info_tbls, which
> > confuses CmmBuildInfoTables
> >
> > Sigh. I don’t know why this only happens on Windows.  I’m looking into a
> > fix
>
> Perhaps this is a problem that only shows up with proc points, which is
> why you wouldn't see it on x86_64/Linux.  Let me know if you get stuck
> and I'll try to look into it.
>
> FYI eliminating always-false stack checks is not new, it was temporarily
> broken by:
>
> commit 94125c97e49987e91fa54da6c86bc6d17417f5cf
> Author: Jan Stolarek <jan.stolarek at p.lodz.pl>
> Date:   Wed Oct 16 09:45:56 2013 +0200
>
>      Generate (old + 0) instead of Sp in stack checks
>
> and then fixed up by:
>
> commit 1cf0c8ad321d1d358cbec46d35be02566faf2d00
> Author: Jan Stolarek <jan.stolarek at p.lodz.pl>
> Date:   Thu Oct 17 23:17:06 2013 +0200
>
>      Optimise stack checks that are always false
>
> Cheers,
> Simon
>
> > Simon
> >
> > *From:*Simon Peyton-Jones
> > *Sent:* 15 November 2013 22:18
> > *To:* ghc-devs at haskell.org
> > *Subject:* bundle panic
> >
> > Windows build is failing again in a new way.  It was fine a couple of
> > days ago. Does this ring any bells?
> >
> > ghc-stage1.exe: panic! (the 'impossible' happened)
> >
> >    (GHC version 7.7.20131107 for i386-unknown-mingw32):
> >
> >       bundle
> >
> > Simon
> >
> > "inplace/bin/ghc-stage1.exe" -static  -H32m -O -Werror -Wall -H64m
> > -O0    -package-name integer-gmp-0.5.1.0 -hide-all-packages -i
> > -ilibraries/integer-gmp/. -ilibraries/integer-gmp/dist-install/build
> > -ilibraries/integer-gmp/dist-install/build/autogen
> > -Ilibraries/integer-gmp/dist-install/build
> > -Ilibraries/integer-gmp/dist-install/build/autogen
> > -Ilibraries/integer-gmp/.    -optP-include
> > -optPlibraries/integer-gmp/dist-install/build/autogen/cabal_macros.h
> > -package ghc-prim-0.3.1.0 -Wall -package-name integer-gmp -XHaskell2010
> > -dcore-lint  -no-user-package-db -rtsopts
> > -Ilibraries/integer-gmp/mkGmpDerivedConstants/dist     -c
> > libraries/integer-gmp/cbits/gmp-wrappers.cmm -o
> > libraries/integer-gmp/dist-install/build/cbits/gmp-wrappers.o
> >
> > ghc-stage1.exe: panic! (the 'impossible' happened)
> >
> >    (GHC version 7.7.20131107 for i386-unknown-mingw32):
> >
> >       bundle
> >
> >      c8 integer_cmm_importIntegerFromByteArrayzh [(c8,
> >
> >                                                    label: block{v
> > c8}_info
> >
> >                                                    rep:StackRep [False,
> > True, True, True]),
> >
> >                                                   (cg,
> >
> >                                                    label: block{v
> > cg}_info
> >
> >                                                    rep:StackRep [False,
> > True, True, True])]
> >
> > Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
> >
> > HEAD (master)$
> >
> >
> >
> > _______________________________________________
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>
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