Two days old build breakage on i386.

Simon Peyton Jones simonpj at
Thu Jun 26 12:47:00 UTC 2014

Thanks.  It’s blocking me from building GHC at all on my laptop, so temporary reversion would be great
Thank you!

From: ghc-devs [mailto:ghc-devs-bounces at] On Behalf Of Johan Tibell
Sent: 26 June 2014 11:38
To: Karel Gardas
Cc: Simon Marlow; ghc-devs
Subject: Re: Two days old build breakage on i386.

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<mailto:karel.gardas at>> wrote:


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:
make[1]: *** [libraries/ghc-prim/dist-install/build/GHC/PrimopWrappers.o] Error 1
libraries/ghc-prim/<>: recipe for target 'libraries/ghc-prim/dist-install/build/GHC/PrimopWrappers.o' failed

Have a look for example on linux-i386 buildot log here:

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<mailto:johan.tibell at>>
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!


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