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cleanup: fix silent miscompiles and delete dead code exposed by code review

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Two correctness bugs were silently producing wrong ROMs:

  - `x << n` / `x >> n` always shifted by 1, regardless of `n`, because
    the IR lowering for `BinOp::ShiftLeft`/`ShiftRight` hardcoded the
    count. Now eval_const the RHS into a compile-time count; fall back
    to a new `IrOp::ShiftLeftVar` / `ShiftRightVar` (runtime loop) when
    the amount isn't constant. Strength reduction folds the variable
    form back to a fixed count once the optimizer knows the value.

  - `x / n` / `x % n` always returned 0, because the lowering emitted
    `LoadImm(t, 0)` for `BinOp::Div`/`Mod` with a comment saying the
    runtime call was "TODO for now". Added real `IrOp::Div` and
    `IrOp::Mod`, wired them through use-counting and DCE, gave codegen
    `__divide`-based implementations, and taught strength reduction to
    rewrite power-of-two divisors into shifts and modulo-by-2ⁿ into
    AND masks. Constant folding now handles `Mul`/`Div`/`Mod`/shifts
    too, which were previously left for the codegen to emit inefficient
    software calls.

Dead code removed (no backward-compat shims kept):

  - `src/debug/` entirely. `DebugSymbols`, `SourceMap`, and the
    Mesen/.sym emitters had no callers outside their own tests;
    `main.rs` never wrote a symbol file. Documented the intent in
    `docs/future-work.md` so it comes back intentionally if needed.
  - `ErrorCode::E0202` (invalid cast) and `E0403` (unreachable state):
    defined, formatted, and marked `#[allow(dead_code)]` but never
    emitted. W0104 now carries the unreachable-state semantics too.
  - `Level::Info`: never constructed.
  - `load_background` / `set_palette` statements and their
    `BackgroundDecl` / `PaletteDecl` parser support: parsed and
    silently dropped by IR lowering (`// TODO: implement in asset
    pipeline`). Removed keywords, AST variants, parser paths, analyzer
    arms, and tests. `docs/future-work.md` documents the runtime
    palette/nametable design for when it comes back.

Doc cleanup:

  - `docs/architecture.md` was describing files that don't exist
    (`analyzer/types.rs`, `optimizer/const_fold.rs`, `codegen/regalloc.rs`,
    `rom/header.rs`, `debug/symbols.rs`, …). Rewrote it to match the
    real flat `mod.rs` + `tests.rs` layout and the real pipeline order.
  - `docs/future-work.md` was a hybrid of open work and "recently
    completed" entries that duplicated the active stubs at the top of
    the file. Collapsed to just the gaps that are actually still open.
  - `README.md` claimed Mesen symbol export and 210 tests; updated both.
  - `docs/language-guide.md` and `spec.md` described `palette` decls,
    `set_palette` / `load_background`, `debug.overlay`, and error codes
    that were never emitted. Trimmed.
  - Stale comments on `Statement::Play`/`StartMusic`/`StopMusic`
    claimed the audio subsystem was "a no-op at codegen time".

Tests:

  - Regression tests for every fix above (`lower_shift_left_with_literal
    _count_uses_that_count`, `lower_shift_right_with_variable_count
    _uses_runtime_variant`, `lower_divide_emits_div_op_not_load_imm
    _zero`, `lower_modulo_emits_mod_op_not_load_imm_zero`,
    `strength_reduce_div_by_power_of_two`, `strength_reduce_mod_by
    _power_of_two`, `strength_reduce_shift_var_with_constant_amount`).
  - Renamed the `program_with_sprites_and_palette` integration test
    (which was exercising the now-removed `load_background`/`set_palette`)
    to `program_with_inline_sprite_chr`.

`examples/sprites_and_palettes.ne` lost its `palette`/`set_palette`
usage. Nothing in the emulator test presses A, so the headless
jsnes render shouldn't move, but the golden may need regeneration
via `UPDATE_GOLDENS=1` if it does.

https://claude.ai/code/session_012fKB251HvEUQwG3tizFyqt
This commit is contained in:
Claude 2026-04-13 02:47:37 +00:00
parent 971a128d0b
commit fdb1ec7c91
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29 changed files with 699 additions and 1157 deletions
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122
src/parser/mod.rs
View file

@ -127,8 +127,6 @@ impl Parser {
let mut functions = Vec::new();
let mut states = Vec::new();
let mut sprites = Vec::new();
let mut palettes = Vec::new();
let mut backgrounds = Vec::new();
let mut sfx = Vec::new();
let mut music = Vec::new();
let mut banks = Vec::new();
@ -165,12 +163,6 @@ impl Parser {
TokenKind::KwSprite => {
sprites.push(self.parse_sprite_decl()?);
}
TokenKind::KwPalette => {
palettes.push(self.parse_palette_decl()?);
}
TokenKind::KwBackground => {
backgrounds.push(self.parse_background_decl()?);
}
TokenKind::KwSfx => {
sfx.push(self.parse_sfx_decl()?);
}
@ -243,8 +235,6 @@ impl Parser {
functions,
states,
sprites,
palettes,
backgrounds,
sfx,
music,
banks,
@ -672,106 +662,6 @@ impl Parser {
})
}
fn parse_palette_decl(&mut self) -> Result<PaletteDecl, Diagnostic> {
let start = self.current_span();
self.expect(&TokenKind::KwPalette)?;
let (name, _) = self.expect_ident()?;
self.expect(&TokenKind::LBrace)?;
let mut colors = None;
while *self.peek() != TokenKind::RBrace && *self.peek() != TokenKind::Eof {
let (key, _) = self.expect_ident()?;
self.expect(&TokenKind::Colon)?;
match key.as_str() {
"colors" => {
self.expect(&TokenKind::LBracket)?;
let mut vals = Vec::new();
while *self.peek() != TokenKind::RBracket && *self.peek() != TokenKind::Eof {
if let TokenKind::IntLiteral(v) = self.peek().clone() {
self.advance();
vals.push(v as u8);
} else {
return Err(Diagnostic::error(
ErrorCode::E0201,
format!("expected color index, found '{}'", self.peek()),
self.current_span(),
));
}
if *self.peek() == TokenKind::Comma {
self.advance();
}
}
self.expect(&TokenKind::RBracket)?;
colors = Some(vals);
}
_ => {
return Err(Diagnostic::error(
ErrorCode::E0201,
format!("unknown palette property '{key}'"),
self.current_span(),
));
}
}
}
self.expect(&TokenKind::RBrace)?;
let colors = colors.ok_or_else(|| {
Diagnostic::error(
ErrorCode::E0201,
"palette requires 'colors' property",
start,
)
})?;
Ok(PaletteDecl {
name,
colors,
span: Span::new(start.file_id, start.start, self.current_span().end),
})
}
fn parse_background_decl(&mut self) -> Result<BackgroundDecl, Diagnostic> {
let start = self.current_span();
self.expect(&TokenKind::KwBackground)?;
let (name, _) = self.expect_ident()?;
self.expect(&TokenKind::LBrace)?;
let mut chr_source = None;
while *self.peek() != TokenKind::RBrace && *self.peek() != TokenKind::Eof {
let (key, _) = self.expect_ident()?;
self.expect(&TokenKind::Colon)?;
match key.as_str() {
"chr" => {
chr_source = Some(self.parse_asset_source()?);
}
_ => {
return Err(Diagnostic::error(
ErrorCode::E0201,
format!("unknown background property '{key}'"),
self.current_span(),
));
}
}
}
self.expect(&TokenKind::RBrace)?;
let chr_source = chr_source.ok_or_else(|| {
Diagnostic::error(
ErrorCode::E0201,
"background requires 'chr' property",
start,
)
})?;
Ok(BackgroundDecl {
name,
chr_source,
span: Span::new(start.file_id, start.start, self.current_span().end),
})
}
// ── SFX / Music declarations ──
/// `sfx Name { duty: N, pitch: [..], volume: [..] }`. Pitch and
@ -1170,18 +1060,6 @@ impl Parser {
self.advance();
Ok(Statement::WaitFrame(span))
}
TokenKind::KwLoadBackground => {
let span = self.current_span();
self.advance();
let (name, _) = self.expect_ident()?;
Ok(Statement::LoadBackground(name, span))
}
TokenKind::KwSetPalette => {
let span = self.current_span();
self.advance();
let (name, _) = self.expect_ident()?;
Ok(Statement::SetPalette(name, span))
}
TokenKind::KwScroll => {
let span = self.current_span();
self.advance();