ABSTRACT:  Compilers often lose optimization opportunities because
they are unable to leverage programmer abstractions.  For example,
expressions involving "Vector" objects might be simplified if the 
compiler was aware of the semantics of a Vector.  In this talk, we
present work done to extend the Mono virtual machine to support 
self-optimizing libraries.  The Mono JIT is modified to export an
optimization API to user code.  Libraries can then be built by users 
that not only provide a user abstraction, but also provide optimizations
that are dynamically detected and added to the extensible JIT compiler
at runtime.  These optimizations can then make use of the semantics
of the abstraction.  The extended framework will be presented and an 
example of a self-optimizing library will be evaluated.