[llvm-dev] PHI node to different register class vs TailDuplication

[Krzysztof Parzyszek via llvm-dev]

On 3/4/2016 6:44 AM, Mikael Holmén via llvm-dev wrote:
>
> Is such a PHI node ok?

That doesn't seem to be well documented. The PHI nodes are described as 
"representing an assignment", but what the "assignment" could be is not 
clear.  Even if there exists an instruction that could copy registers 
between register classes, if you cannot substitute the output operand 
with one of the input operands in any use of the output, the PHI would 
seem to be malformed.  At least, that is my interpretation.

-Krzysztof

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