[EPIC] Fork/Join Parallel Ranges

[jrhemstad]

Looking towards the future of C++ parallel algorithms, <ranges> are becoming the canonical model for expressing and composing algorithms with arbitrary transformations. As such, we want the next generation of Thrust/CUB-like parallel algorithms to be based on ranges.

Thus far, <ranges> has been designed primarily with sequential execution in mind. In order for us to build a next generation set of parallel algorithms and utilities, we will need to investigate to what extent the existing <ranges> design supports parallel execution.

The high-level goal is that we should be able to use a ranges-based interface to express anything we are able to express today with Thrust + fancy iterators with equal or better expressiveness and performance.

• [EPIC] Heterogeneous, sequential ranges support #45
• [FEA]: Identify challenges with existing ranges machinery when used with parallel execution #48
• Proof-of-concept parallel ranges algorithms #1213
• [FEA]: Provide std::algorithms to be usable on device #1183
• [FEA]: Provide <ranges> algorithms #1184