Pulley TODO List

[alexcrichton]

I'd like a place to throw small items as I see them and to collect various TODO items during the development of Pulley. For now this will serve that location. My hope is that this list is TODO items which pertain to code in-tree and are less-so about wishlist items of what's yet to fill in. For example this won't track missing pulley work (e.g. all wasm proposals at this time). Unsure if this style of issue will work out.

• Support building Wasmtime with the Pulley interpreter but not the Pulley compiler
• Move sp/fp/lr/special regs out of the general purpose register set; see pulley: Implement get_frame_pointer #9658 (review) for details (also cc pulley: Move fp/lr out of XReg set #9806)
• Assert in call lowering that pulley<->pulley is always tail-to-tail or similar; see pulley: Implement interpreter-to-host calls #9665 (comment) for details -- pulley: Assert calling-conventions match instructions #9836
• Better debugging support, e.g. print the register state between instructions and print each instruction. pulley: Add simple debugging support #9796
• Support big-endian - will need to add pulley{64,32}be targets to target-lexicon, then add big-endian loads/stores, then update the CLIF backend to delegate to the right endianness based on the target
• Need to restore callee-save state when a trap happens somehow (either via explicit saves or by removing callee-save state in that situation)
• Evaluate 32-bit platforms and the decision to "only write low 32-bits". If we write the full 64-bit width of registers does it actually have a performance loss? Is it worth burning opcode space for opcodes that only write the low-32 instead of high 64? Should we split opcodes like xconst8 into one that writes 64-bits and one that writes 32-bits? Should we remove xload8_s32_offset32 instead?
• Explore adding new addressing modes (e.g. register + register). Should be based on an evaluation of what wasm loads/stores do probably. Perhaps even fold a trapping arithmetic into one macro-op for "do the wasm load on 32-bit" and "do the wasm load on 64-bit"
• Enable Cranelift runtest support pulley: Support runtests in Cranelift filetests #9795
• Run the full all test suite on 32-bit platforms -- Run the full test suite on 32-bit platforms #9837
• Add support for Pulley to #[wasmtime_test]
• Figure out story for threading -- loads/stores all need to be at least with a "relaxed" atomicity -- pulley: Disable the WebAssembly threads proposal #9818

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[alexcrichton]

Notes for big-endian:

• Need to add big-endian targets for Cranelift -- Add big-endian Pulley targets target-lexicon#115
• Pulley loads/stores will all have annotated endianness, nothing is "native endian"
• New big-endian loads/stores to get added under the "extended" opcode space
• Cranelift will use its configuration to select the appropriate pulley instruction, e.g. "native endianness" is whatever the configured target uses