llvm dev - Feb 2016 - How to interpret Selection DAG error output

I recently had to change some DAG patterns for my target. Conceptually I
understand what DAG patterns are and what is their purpose, however given
that I have quite vague understanding about how to LLVM implements and
specifies them, naturally I got an error. Here it is

Here is the error:

LLVM ERROR: Cannot select: 0x3284268: glue = EsenciaISD::SET_FLAG
0x3283608, 0x3283710, 0x3283e48 [ORD=3] [ID=11]
  0x3283608: i32,ch = CopyFromReg 0x3257980, 0x3283500 [ORD=1] [ID=9]
    0x3283500: i32 = Register %vreg5 [ID=1]
  0x3283710: i32 = Constant<3> [ID=2]
  0x3283e48: i32 = Constant<20> [ID=8]
In function: fib

As far as I can understand LLVM cannot select it because the pattern is not
specified. Unfortunately for me, I can't understand how to interpret this
output. Would anybody be able to help me out?

Any help is appreciated.

-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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On 2/18/2016 12:43 PM, Rail Shafigulin via llvm-dev
wrote:
>
> LLVM ERROR: Cannot select: 0x3284268: glue = EsenciaISD::SET_FLAG
> 0x3283608, 0x3283710, 0x3283e48 [ORD=3] [ID=11]
>    0x3283608: i32,ch = CopyFromReg 0x3257980, 0x3283500 [ORD=1] [ID=9]
>      0x3283500: i32 = Register %vreg5 [ID=1]
>    0x3283710: i32 = Constant<3> [ID=2]
>    0x3283e48: i32 = Constant<20> [ID=8]
> In function: fib
>
> As far as I can understand LLVM cannot select it because the pattern is
> not specified. Unfortunately for me, I can't understand how to
interpret
> this output. Would anybody be able to help me out?

The DAG node that has failed selection is "SET_FLAG %vreg5, 3, 20",
the
type of the node is "glue" and all 3 arguments are i32.

The top line shows the node that caused the failure.  The hex numbers on 
that line are the addresses of the arguments.  These arguments are then 
listed below.

Newer versions of LLVM show node ids instead of addresses, but AFAIK it 
was dependent on some configuration option.

-Krzysztof


-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, 
hosted by The Linux Foundation

Thanks for the explanation. Do you know what ORD and ID mean?

On Thu, Feb 18, 2016 at 10:50 AM, Krzysztof Parzyszek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 2/18/2016 12:43 PM, Rail Shafigulin via llvm-dev wrote:
>
>>
>> LLVM ERROR: Cannot select: 0x3284268: glue = EsenciaISD::SET_FLAG
>> 0x3283608, 0x3283710, 0x3283e48 [ORD=3] [ID=11]
>>    0x3283608: i32,ch = CopyFromReg 0x3257980, 0x3283500 [ORD=1] [ID=9]
>>      0x3283500: i32 = Register %vreg5 [ID=1]
>>    0x3283710: i32 = Constant<3> [ID=2]
>>    0x3283e48: i32 = Constant<20> [ID=8]
>> In function: fib
>>
>> As far as I can understand LLVM cannot select it because the pattern is
>> not specified. Unfortunately for me, I can't understand how to
interpret
>> this output. Would anybody be able to help me out?
>>
>
>
> The DAG node that has failed selection is "SET_FLAG %vreg5, 3,
20", the
> type of the node is "glue" and all 3 arguments are i32.
>
> The top line shows the node that caused the failure.  The hex numbers on
> that line are the addresses of the arguments.  These arguments are then
> listed below.
>
> Newer versions of LLVM show node ids instead of addresses, but AFAIK it
> was dependent on some configuration option.
>
> -Krzysztof
>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>


-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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On Thu, Feb 18, 2016 at 10:50 AM, Krzysztof Parzyszek via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> On 2/18/2016 12:43 PM, Rail Shafigulin via llvm-dev wrote:
>
>>
>> LLVM ERROR: Cannot select: 0x3284268: glue = EsenciaISD::SET_FLAG
>> 0x3283608, 0x3283710, 0x3283e48 [ORD=3] [ID=11]
>>    0x3283608: i32,ch = CopyFromReg 0x3257980, 0x3283500 [ORD=1] [ID=9]
>>      0x3283500: i32 = Register %vreg5 [ID=1]
>>    0x3283710: i32 = Constant<3> [ID=2]
>>    0x3283e48: i32 = Constant<20> [ID=8]
>> In function: fib
>>
>> As far as I can understand LLVM cannot select it because the pattern is
>> not specified. Unfortunately for me, I can't understand how to
interpret
>> this output. Would anybody be able to help me out?
>>
>
>
> The DAG node that has failed selection is "SET_FLAG %vreg5, 3,
20", the
> type of the node is "glue" and all 3 arguments are i32.
>
I understand where SET_FLAG, 3 and 20 come from, but how did you arrive the
conclusion that %vreg5 should be part of the pattern?

> The top line shows the node that caused the failure.  The hex numbers on
> that line are the addresses of the arguments.  These arguments are then
> listed below.
>
> Newer versions of LLVM show node ids instead of addresses, but AFAIK it
> was dependent on some configuration option.
>
> -Krzysztof
>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>


-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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On 18 Feb 2016, at 18:43, Rail Shafigulin via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> As far as I can understand LLVM cannot select it because the pattern is not
specified. Unfortunately for me, I can't understand how to interpret this
output. Would anybody be able to help me out?
You’ve had a few answers already, but just to add one more:

SelectionDAG has a viewGraph family of methods, that will dump a .dot file and
open it with GraphViz.  These can be run from the debugger and produce *much*
more readable output.  When I’m debugging, I generally stick a breakpoint on the
code that’s triggering this error and get the pretty picture to try to figure
out what’s going on.  It’s a lot easier to understand for nontrivial examples.

David