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

Krzysztof Parzyszek via llvm-dev llvm-dev at lists.llvm.org
Thu Feb 18 11:34:46 PST 2016

On 2/18/2016 1:32 PM, Rail Shafigulin wrote:
> I think this is where I'm loosing the "thread". Based on what I'm seeing
> SET_FLAG has three operands, the first of which is a CopyFromReg. So how
> come the pattern is SET_FLAG %vreg5, 3, 20 and not SET_FLAG CopyFromReg,
> 3, 20? In other words how do we go from CopyFromReg to %vreg5?

CopyFromReg is a "helper" instruction meaning "use the value from this 
vreg".  Values that are live across basic blocks are remembered in 
vregs, and CopyToReg and CopyFromReg are opcodes used to express it.


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