[llvm-dev] How to interpret Selection DAG error output

[Krzysztof Parzyszek via llvm-dev]

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

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