Two days old build breakage on i386.

[Johan Tibell]

I think it's reasonable to say my change triggers the issue, but I don't
know why and I need someone who understand the register allocator better
(e.g. Simon M) to at least give me some pointers on how to debug this. If
this is causing more trouble than build bot breakages (which is bad
enough), let me know and I'll either revert temporarily and or try to work
around the issue.

Also, how do I repro this if I don't have a x86 machine lying around? Have
people been successful working on these kind of issues in a VM?


On Thu, Jun 26, 2014 at 10:55 AM, Karel Gardas <karel.gardas at centrum.cz>
wrote:

>
> Hello,
>
> builders running on i386 building for this platform caught issue which
> shows as a build breakage:
>
> ghc-stage1: panic! (the 'impossible' happened)
> (GHC version 7.9.20140624 for i386-unknown-linux):
> RegAllocLinear.allocRegsAndSpill: no spill candidates
> allocating vreg: VirtualRegI n1Q6
> assignment: [(c1PV,InMem 2),(n1Q5,InBoth (RealRegSingle 3) 0),(n1Q6,InMem
> 1),(n1Q7,InMem 3),(n1Q9,InReg (RealRegSingle 2))]
> freeRegs: FreeRegs 4282318848
> initFreeRegs: FreeRegs 4282318861
> Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
> make[1]: *** [libraries/ghc-prim/dist-install/build/GHC/PrimopWrappers.o]
> Error 1
> libraries/ghc-prim/ghc.mk:4: recipe for target 'libraries/ghc-prim/dist-
> install/build/GHC/PrimopWrappers.o' failed
>
> Have a look for example on linux-i386 buildot log here:
> http://haskell.inf.elte.hu/builders/validator1-linux-x86-head/18/7.html
>
> Anyway, this happens on Linux, FreeBSD and Solaris buildbots on i386 so
> it's OS independent and probably 32bit/i386 platform specific and it's two
> days old breakage now. The last two night builds fail on all mentioned
> buildbots. I'm not sure but perhaps:
>
> commit d8abf85f8ca176854e9d5d0b12371c4bc402aac3
> Author: Johan Tibell <johan.tibell at gmail.com>
> Date:   Mon Jun 9 11:43:21 2014 +0200
>
> triggers that issue? I'm not claiming that the commit is actual culprit,
> this may be just recently un-hidden issue in linear regs allocator on i386!
>
> Thanks!
> Karel
>
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