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

On Thu, Feb 18, 2016 at 11:48 AM, Krzysztof Parzyszek <
kparzysz at codeaurora.org> wrote:
> On 2/18/2016 1:40 PM, Rail Shafigulin wrote:
>
>>
>>            0x3283608: i32,ch = CopyFromReg 0x3257980, 0x3283500 [ORD=1]
>>          [ID=9]
>>                0x3283500: i32 = Register %vreg5 [ID=1]
>>
>> Based on the code above, CopyFromReg is a node at address 0x3283608,
>> returns i32, is of type chain and takes two inputs, the second of which
>> is a %vreg5. So what is the first parameter? In fact where can I find
>> the definition of CopyFromReg method?
>>
>
> The first parameter is a chain.
>
> Here are some comments from include/llvm/CodeGen/ISDOpcodes.h:
>
>     /// CopyToReg - This node has three operands: a chain, a register
> number to
>     /// set to this value, and a value.
>     CopyToReg,
>
>     /// CopyFromReg - This node indicates that the input value is a
> virtual or
>     /// physical register that is defined outside of the scope of this
>     /// SelectionDAG.  The register is available from the RegisterSDNode
> object.
>     CopyFromReg,
>
> I usually grep the sources if I want to find out about something.  I'm
not
> sure if there is a better documentation about ISD nodes.

Thanks. I keep forgetting that I have grep at my disposal :) What I'm not
clear about is the first parameter in CopyFromReg node.  0x3283608: i32,ch
= CopyFromReg 0x3257980, 0x3283500 [ORD=1]. Based on the comments for
CopyFromReg, if I understand it correctly, there should be 1 input, virtual
or physical register, which is what is given in the pattern as a second
argument. So what is the first one. What does it do?

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


-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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On 2/18/2016 2:18 PM, Rail Shafigulin wrote:
> Thanks. I keep forgetting that I have grep at my disposal :) What I'm
> not clear about is the first parameter in CopyFromReg node. 0x3283608:
> i32,ch = CopyFromReg 0x3257980, 0x3283500 [ORD=1]. Based on the comments
> for CopyFromReg, if I understand it correctly, there should be 1 input,
> virtual or physical register, which is what is given in the pattern as a
> second argument. So what is the first one. What does it do?
It's a chain, it's used to maintain relative ordering between nodes. 
Both CopyToReg and CopyFromReg have the same arguments.  I agree, it's 
not clear from the comments.

-Krzysztof

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

On Thu, Feb 18, 2016 at 12:20 PM, Krzysztof Parzyszek <
kparzysz at codeaurora.org> wrote:
> On 2/18/2016 2:18 PM, Rail Shafigulin wrote:
>
>> Thanks. I keep forgetting that I have grep at my disposal :) What
I'm
>> not clear about is the first parameter in CopyFromReg node. 0x3283608:
>> i32,ch = CopyFromReg 0x3257980, 0x3283500 [ORD=1]. Based on the
comments
>> for CopyFromReg, if I understand it correctly, there should be 1 input,
>> virtual or physical register, which is what is given in the pattern as
a
>> second argument. So what is the first one. What does it do?
>>
>
> It's a chain, it's used to maintain relative ordering between
nodes. Both
> CopyToReg and CopyFromReg have the same arguments.  I agree, it's not
clear
> from the comments.

Thanks for the explanation.
>
>
> -Krzysztof
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted
> by The Linux Foundation
>


-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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