Annotations as alternative to IR extension need reviewing for their ease of use

[jvansomeren]

The IR is static and only extensible by annotations.
Annotations essentially are a map from annotation name to value.
They are used e.g. to represent the ddg.

The interfaces are significantly harder to use than the plain IR accesses.
Need to review this.
Is there an option to make the IR extensible?
Otherwise, we look through the interfaces: is the documentation understandable?
Could the interface be easier?