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

[Krzysztof Parzyszek via llvm-dev]

Your type-legalized selection DAG has nested callseq_start/callseq_end. 
I don't know if this is the root cause, but I'd fix that first. It may 
be, given that your assertion happens around ADJCALLSTACKUP/ 
ADJCALLSTACKDOWN nodes.

-Krzysztof


On 7/29/2016 3:04 PM, Elliot Colp via llvm-dev wrote:
> 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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