[llvm-dev] Understanding failed assert in reg pressure reduction list scheduler

[Elliot Colp via llvm-dev]

Sure, I've attached it to the bug report. Direct link is here:
https://llvm.org/bugs/attachment.cgi?id=16840

- Elliot

"llvm-dev" <llvm-dev-bounces at lists.llvm.org> wrote on 2016/07/29 03:46:41
PM:

> From: Krzysztof Parzyszek via llvm-dev <llvm-dev at lists.llvm.org>
> To: llvm-dev at lists.llvm.org
> Date: 2016/07/29 03:46 PM
> Subject: Re: [llvm-dev] Understanding failed assert in reg pressure
> reduction list scheduler
> Sent by: "llvm-dev" <llvm-dev-bounces at lists.llvm.org>
>
> Could you post the .ll file with the testcase?
>
> -Krzysztof
>
>
> On 7/29/2016 2:38 PM, Elliot Colp via llvm-dev wrote:
> > Hi all,
> >
> > I'm currently investigating a bug which is causing an assert to fail in
> > lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp. See
> > https://llvm.org/bugs/show_bug.cgi?id=28753 for repro information.
> >
> > To my knowledge, this problem only occurs with the SystemZ target. I'm
> > trying to determine whether the issue is the result of an edge case in
> > the scheduling code itself, or if it's a SystemZ target problem.
> > However, I'm unfamiliar with the scheduling code, so I'm not entirely
> > certain what the correct behaviour is.
> >
> > My rough understanding of the problem is that, while attempting to pick
> > a node to schedule, we're running out of candidates (in
> > ScheduleDAGRRList::PickNodeToScheduleBottomUp). This causes us to try
to
> > copy a node, and in the process, we call getPhysicalRegisterVT. This
> > function asserts that the MCInstrDesc associated with the node will
have
> > ImplicitDefs, but in our case, it does not.
> >
> > In short: does this seem to be a problem of missing information in the
> > MCInstrDesc, or should we not have arrived at that assert in the first
> > place?
> >
> > Thanks,
> >
> > - Elliot
> >
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
>
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