Roadmap update from Nekotekina (25-07-2022)

Hello,

Sorry for not talking much. This short post will only focus on work in progress and further plans.

• Accuracy improvements in PPU/SPU. Despite its good compatibility, RPCS3 currently doesn't have accurate implementation of certain basic features of PS3 CellBE processor. This includes approximation instructions, which are lazily implemented to be "good enough" and produce different results. Inaccurate implementations may cause various bugs and incompatibilities.
• New decoder (recompiler) modes. There is a plan to implement a new recompiler mode for PPU which doesn't require heavy precompilation stage as PPU LLVM does. It's currently called Interpreter (dynamic), but naming may change since this is something closer to SPU ASMJIT recompiler. In earlier posts, I mentioned plans to implement LLVM-based interpreter for PPU, but this plan is now cancelled due to the lack of necessity. It was supposed to solve accuracy differences between Interpreter and LLVM Recompiler, but those can be solved directly. In fact, many of them are already fixed, but I will save this for an actual progress report. Now SPU needs some cleanup in this area as well. SPU ASMJIT may even be rewritten with some optimizations.
• A utility similar to "KnownBits" in LLVM but implemented differently from top to bottom. It may improve recompiler efficiency by propagating certain information about numeric values during the computations. I mentioned it as "constant propagation" in previous reports but it's not a very accurate naming. In some sense, it's capable of telling that something is always constant about numbers, as one is always even or odd for example.
• Aarch64 support. It was demonstrated that some ARM processors are capable of running RPCS3 just fine, so I laid some groundwork for those in January, but there is a lot to do yet.
• ISO boot support. Small QoL improvement that is often asked for.

As always, thank you for support.