Stackless generator: record locals / record yield element (chess GenMoves wall #2)

• Type: feature (compiler restriction lift)
• Track: A — compiler/parser.inc (stackless generator transform)
• Status: backlog
• Opened: 2026-07-02

Problem

With yield-in-case lifted (feature-stackless-generator-yield-in-case, done 2026-07-02), the NEXT wall between examples/chess/chess.pas and cross-target builds is:

pascal26:634: error: stackless generator: only ordinal/pointer locals are supported (v1) ()

GenMoves(const pos: TPosition): TMove; generator; stackless; yields a RECORD (TMove) and keeps record locals across yields. The v1 stackless instance layout persists locals as single 8-byte words (SL_OFF_SLOTS + 8*slot), so records (multi-word) can't be checkpointed, and the yielded CURRENT slot is one word too.

Scope

• Persist record locals across yields: byte-copy the record into/out of a correctly-sized instance region (slot allocation by size, not word count).
• Support a record element type for the generator (CURRENT becomes a record-sized region; for-in copies it out).
• const record params (pos: TPosition) may already work via pointer-word persistence — verify.

Acceptance

• A stackless generator with a record local + record element compiles and runs correctly on x86-64 + i386.
• examples/chess/chess.pas (with stackless added to GenMoves) builds and passes perft on the cross targets — the remaining chess acceptance from the yield-in-case ticket.
• Existing test/test_stackless_gen.pas stays green; self-host byte-identical.

Log

• 2026-07-02 — Filed by Track A while resolving feature-stackless-generator-yield-in-case: case restriction lifted, chess's GenMoves now stops at this wall instead (also note chess.pas declares plain stackful generator; — cross builds additionally need the stackless keyword on GenMoves, i.e. a one-word source tweak, Track B's call).
• 2026-07-02 — Track A: DONE.
  • Record LOCALS persist across yields: multi-word slot regions (RecSize-rounded), SlBlob/SlUnblob byte-copy save/restore (new slgen helpers). Managed-field records rejected cleanly.
  • Record ELEMENT type: record-sized CURRENT region reserved at the instance tail; yield blob-copies the (always-lvalue, parse-site-materialised) record and publishes the region address in the CURRENT word; for-in derefs it into the loop var (mirrors the stackful CoCurrent shape).
  • By-ref (var/const-record) params persist their POINTER WORD via new AN_SLOTADDR (=77, lowers to existing IR_SLOTADDR) — a plain assign to an IsRef sym stores THROUGH the caller address. Pointer-typed deref (native width — Int64 clobbered the neighbour slot on 32-bit targets).
  • Step-call pad args for by-ref params use an addressable ident (a zero literal has no address for the by-ref marshalling path).
  • continue/break inside a FLATTENED loop rewritten to gotos (SLRewriteLoopJumps; for-loop continue targets a new inc label).
  • SlAlloc (6×Int64 = 12 arg words, over riscv32's 8-word limit) replaced by SlNew + per-arg SlSet; AsyncGo switched too.
  • aarch64 IR_SLOTADDR fixed to the raw-slot contract (was auto-dereffing by-ref params via EmitLoadVarAddrA64 — x64/i386/arm32 were already raw).
  • MAX_GOTO_LABELS 64 -> 2048 (chess GenMoves needs hundreds); BlockParent 8192 -> 32768 (FPC cold bootstrap, cap was baked into the compiling binary).
  • Validated: test_stackless_gen.pas extended (RecGen: record local mutated across resume, call-result yield, const-record param, continue, case) — output-identical on x86-64/i386/aarch64/arm32. Stackless chess variant: perft selftest CHECKSUM identical to stackful on x86-64.
  • Chess CROSS builds still walled — but no longer by generators: readln unsupported on cross backends (filed feature-cross-readln-console-input); riscv32 hosted writeln hangs even on pinned v154 (pre-existing, filed bug-riscv32-hosted-writeln-hello-hangs).