When generating both heap and stack checks in Cmm, GHC can sometimes be fairly obtuse about their placement. As a result, they can be generated for paths in hot code that actually do not perform any allocation. Examples can be found in the related tickets, particularly #14791 and #16040.

This ticket exists to track the work proposed by Simon to detect such code patterns. They are described as follows:

1. A primitive case with no allocation upstream from it.
2. One alternative that performs no allocation.

Under such circumstances the stack/heap checks can be moved from being performed on every iteration to being performed just prior to the allocation itself.