Description
Inlinee compilers allocate their blocks in the root compiler's flow graph pool, and use the root compiler's block numbering.
Because of this, running analysis on the inlinee compiler's flowgraph "fragment" proves tricky. We got a taste of this in #80958, where I had to introduce fgBBNumMin, whose value is only 1 for the root compiler.
For example, to use a BlockSet one must either use the root compiler's epoch (in which case the bit vectors and scratch storage based on fgBBNumMax are much too large) or else remember to consistently things downward (like bbID) by fgBBNumMin.
This impacts a lot of flow utility methods that might be useful to run on inlinee flowgraph fragments, eg fgDfsReversePostorder (see #82752).
It would be helpful to come up with a better model so that code can be written "naturally" but properly handle cases where it's invoked on inlinee graphs.