fast-isel use of tablegen patterns

Is there something special to do in order to turn on the use of tablegen patterns for fast-isel.
I know that we are generating the fast-isel files for mips.

For example:

it gets a :

FastISel miss: %add = add nsw i32 %1, %0

But we have the underlying structure for this.

I.e. i can assign literals to int globals and such.

And we have the pattern for matching "add".

Is there an easy way to trace this?

TIA.

Reed