What is a pass manager?
A pass manager is a driver for the set of passes that you want to run.
It fulfills three main functions:
- It provides a structure to run passes in a specific order.
- It makes sure that the dependencies of a pass are properly executed before the pass itself.
- It preserves or invalidates the various analyses based on the passes’ effects.
When a pass manager invokes a pass, it also provides specific guarantees on the order in which the IR is visited.
These guarantees are as follows:
- For CGSCC-scoped passes, a pass manager invokes the pass on the leaf strongly connected component (SCC) regions first then moves up in the call graph.
- For loop-scoped passes, loops are visited following their nested level from innermost to outermost loops.
- For region-scoped passes, the nesting level is also used in a similar fashion: from the innermost region to the outermost regions.
- For other scopes, the order...
