Dependency Graph

[martin-ueding]

We start to realize that our heuristic ad-hoc dependency tracking is an improvement over the inconsistent explicit loops where one has no dependency abstraction but fails shorts of delivering a really good way of organizing the work. At the current stage the memory requirement scales with the number of threads p as O(p) which severely limits us on most machines. Additionally we don't know how much memory we really need for what.

By introducing a dependency graph we would have full knowledge of what to build, would know how much memory every node needs and could do optimal subgraph traversal for maximal re-use.

This issue shall contain the discussion and the accompanying Dependency Graph wiki page shall contain the design of that feature such that it can serve as documentation later on.