`remove_dead_loads` now scans past opcodes that touch neither A nor
the flags an LDA sets, so a redundant LDA gets caught by its
successor's overwrite even when an index load or counter bump sits
between them. The extension covers LDX/LDY/INX/INY/DEX/DEY and the
flag ops (CLC/SEC/CLI/SEI/CLD/SED/CLV) alongside the INC/DEC/STX/STY
opcodes the pass already stepped past.
The highest-leverage case is the shape every single-tile `draw`
emits. After copy propagation and dead-store elimination do their
work, the stream reads:
LDA #<y> ; stray producer, value never consumed
LDY oam_cursor
LDA #<y> ; real load before STA
STA $0200,Y
The first LDA was surviving because the pass bailed on the LDY.
With the step-past, it drops. One LDA gone per draw, 2 bytes each.
Measured LDA-count reduction on committed examples:
platformer 242 → 221 (-21, -8.7 %)
war 785 → 754 (-31, -4.0 %)
pong 843 → 827 (-16, -1.9 %)
**Audio goldens.** The cycle savings shift the main-loop/NMI boundary
in audio-emitting programs, which re-times which frame each SFX
trigger lands in. Six audio hashes re-baseline as a result:
audio_demo, friendly_assets, noise_triangle_sfx, platformer, pong,
war. All 50 PNG goldens, the platformer/war/pong demo gifs, and
every non-audio program stay byte-identical. The re-baselined
output is still sample-accurate; what changed is the first-SFX
offset within the captured 132 084-sample window. This is the
audio-shift tradeoff documented in future-work.
Two new peephole unit tests lock in the behaviour:
- `dead_load_elim_steps_past_ldx_ldy` — the DrawSprite shape folds.
- `dead_load_elim_preserves_lda_when_used_by_shift` — a subsequent
ASL on A keeps the LDA alive across an intervening LDY.
Also updates future-work.md to reflect the shipped change and the
remaining register-allocator wins worth chasing next.
Another batch from the cc65/nesdoug catalogue. All gated on
parser-level opt-in or default-false attributes so existing
programs produce byte-identical ROMs (no committed .nes file
changed).
**§A — `i16` signed 16-bit type:**
- New `KwI16` lexer token, `NesType::I16` AST variant, parser
case in `parse_type`. Type-size and integer-type tables
treat `i16` like `u16` (2 bytes, integer).
- IR lowering accepts `i16` everywhere it accepts `u16` for
wide-load / wide-store / widen-narrow paths.
- New constant fold for `UnaryOp::Negate(IntLiteral(v))` that
emits the wide two's-complement form. Without it, `var vy:
i16 = -10` would zero-extend to `$00F6` (= 246) instead of
sign-extending to `$FFF6` (= -10). Negative literals now
store the right bytes.
- Comparisons reuse the existing unsigned 16-bit compare ops
(matching the existing `i8` behaviour). Documented in the
`NesType::I16` doc comment and in `future-work.md` §A.
- Example `examples/i16_demo.ne` with committed golden.
- Tests cover the literal-fold sign-extension and end-to-end
compile of the example.
**§S — SRAM / battery-backed saves:**
- New `save { var ... }` top-level block. Lexer + parser opt
into a dedicated `KwSave` token. Analyzer allocates save
vars from a separate `next_sram_addr` bump pointer starting
at `$6000`, capped at `$8000` (8 KB cartridge SRAM window).
- Linker reads `analysis.has_battery_saves` and flips iNES
byte-6 bit-1 via the new `RomBuilder::set_battery` /
`Linker::with_battery` chain.
- New `W0111` warning for save-var initializers — SRAM is
preserved across power cycles, so an init expression would
either silently never run or clobber persisted data on
every boot. The warning teaches the user about the
magic-byte sentinel pattern.
- Struct fields in save blocks are explicitly rejected for now
(the field-flattening path uses the main-RAM allocator).
- Example `examples/sram_demo.ne` with committed golden, plus
4 integration tests.
**§D (partial) — inline-asm `.label:` syntax:**
- Codegen-side mangler rewrites `.IDENT` → `__ilab_<N>_IDENT`
per inline-asm block, where `<N>` is the call site's
monotonic suffix. Two `asm { .loop: ... }` blocks in the
same function now coexist without colliding in the linker's
label table.
- Bounds checks on `.` placement: `$2002` and `name.field`
are unaffected; only `.IDENT` in label / branch context
triggers the rewrite. Two integration tests pin the
uniqueness and dollar-vs-dot disambiguation.
**§X follow-up — Mesen trace-log docs:**
- New "Debugger-assisted workflows" section in
`docs/nes-reference.md` walking through the Mesen / FCEUX
log workflows alongside the new `debug_port:` attribute.
**Misc:**
- `future-work.md` updated to mark the shipped items out of
the catalogue and reshuffle the priority ranking. Remaining
niche follow-ups (signedness on Cmp16, struct save fields,
inline-asm format specifiers) documented inline so future
passes know the design.
All 757 tests pass. Clippy clean. 46/46 emulator goldens match.
