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https://github.com/imjasonh/nescript
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0602fd9590
Follow-up to the silent-drop audit. The old ABI passed every parameter through four fixed zero-page transport slots `$04-$07`, imposing a hard 4-param cap (E0506) that didn't compose with structs/arrays/u16s and fell back to "pack args into a global" workarounds whenever a function needed five things. The transport scheme also cost every non-leaf call a 4-LDA/STA spill prologue (~28 cycles, 16 bytes) to copy args out of ZP before the next nested `JSR` could clobber them. Replace it with a hybrid convention keyed on leaf-ness: - **Leaf callees** (no nested `JSR` in body, ≤4 params): unchanged. Caller stages args into `$04-$07`; body reads those slots directly for its entire lifetime. No prologue copy. Fastest path, 3-cycle ZP stores + 3-cycle ZP loads, preserves the SHA-256 leaf-primitive optimisation that motivated the original fast path. - **Non-leaf callees** (body contains a nested `JSR`, OR ≥5 params): direct-write. Caller stages each argument straight into the callee's analyzer-allocated parameter RAM slot, bypassing the transport slots entirely. No prologue copy on the callee side. Saves ~24 cycles and ~16 bytes per call vs the old transport-then-spill path, and — crucially — scales past 4 params because the per-param slots live wherever the analyzer put them rather than in a fixed ZP window. The analyzer's ceiling moves from 4 to 8. Functions with 5–8 params are silently promoted to the non-leaf convention (even if their body has no nested `JSR`), which pays the direct-write cost rather than the prologue-copy cost — still cheaper than the old ABI. Declarations with 9+ params still emit E0506. ### Implementation - `function_is_leaf` now also requires `param_count <= 4`. - `IrCodeGen::new` populates `non_leaf_param_addrs: HashMap<String, Vec<u16>>` — for every non-leaf function, the ordered list of addresses its parameters occupy. Callers use this to route each arg directly to the right slot. - `IrOp::Call` branches on presence in the map: non-leaf → direct- write, leaf (or absent — 0-arg case) → ZP transport. - `gen_function` no longer emits a prologue. Leaves didn't have one; non-leaves had a 4-LDA/STA copy that is now unnecessary because args arrive pre-written to the slot. - The previous `leaf_functions: HashSet<String>` field is removed; leaf-ness is now inferred from absence-in- `non_leaf_param_addrs` at the call site. ### Tests and regressions - `eight_param_non_leaf_function_stages_every_arg_at_its_allocated_slot` compiles an 8-param function, scans PRG for a distinct `LDA #\$NN / STA <addr>` per arg (immediates `0x11..0x88`), and asserts that STAs to the `$04-$07` range are strictly fewer than 8 — proof the old transport path is gone for this call. - `non_leaf_call_direct_writes_args_to_callee_param_slots` replaces the old `gen_function_prologue_spills_params_to_local_ram` test with a dual assertion: (a) no `LDA \$04` prologue at the callee entry, and (b) the caller-side STA lands at the analyzer-allocated param slot, not at `\$04-\$07`. - `analyze_rejects_function_with_more_than_4_params` renamed and rewritten for the new 8-param cap. - `feature_canary.ne` gains a 6-param `sum6` call (1+2+3+4+5+6 = 21) as check 8. The canary stays green (all eight checks pass), so the committed golden is unchanged. ### Blast radius - Six example ROMs change bytes (arrays_and_functions, function_chain, mmc1_banked, pong, sha256, war) because their non-leaf call sites pick up the shorter staging sequence. - Pong and war audio hashes refresh (pure layout-timing shift; no behavioural change in the 180-frame no-input window). docs/pong.gif and docs/war.gif stay byte-identical. - `examples/function_chain.ne`'s header comment updated to document the leaf vs non-leaf split it exercises. - `docs/language-guide.md` parameter-count section and E0506 entry updated to reflect the new rule. All 720 Rust tests pass; all 35 emulator goldens pass. https://claude.ai/code/session_01AoQ678uVeqpyayvWHpfDhC |
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