unspec expressions

[Ranjit Singh]

Hi,

I am trying to understand RTL representation.
I have a question about unspec expressions.

The manual says
(unspec [operands ...] index) 
(unspec_volatile [operands ...] index) 
 Represents a machine-specific operation on operands. 

 index selects between multiple machine-specific
 operations

1. How are these expresions used and How does
construction and matching take place in this
case (if they occur in define_insns)?
An example would be helpful.

Thanks,
Ranjit.

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