12552e125d
Two silent-miscompile codegen fixes:
0083 — named-const array dimension. `TypeResolver.resolveCompound`'s array
arm resolved the dimension with `if int_literal ... else 0`, so a named const
(`N :: 16; [N]T`) hit the silent `else 0`: the array became 0-length / 0-byte
and element access ran out of bounds (garbage for scalars, bus error for
slice/pointer/struct elements). The arm now delegates the dimension to
`inner.resolveArrayLen` (symmetric with `inner.resolveInner` for the element).
The stateful `Lowering.resolveArrayLen` evaluates it as a compile-time integer
across the comptime-constant / generic-value / module-global const tables and
emits a diagnostic — no fabricated length — when it isn't one.
0084 — `.[...]` literal passed directly as a call arg. `lowerArrayLiteral`
always yields an aggregate array value; the array→slice conversion is the
caller's job. The local-bound var-decl path did it, but the call-arg coercion
path had no array→slice arm, so `classify([N]T, []T)` returned `.none` and the
raw array was passed where a slice was expected (callee read its {ptr,len}
header off the wrong bytes → 0 / garbage / segfault). `classify` now returns a
new `.array_to_slice` plan for same-element `[N]T → []T`, and `coerceToType`
emits the existing `array_to_slice` op — identical to the local-bound path.
Regressions (fail-before/pass-after demonstrated on the pre-fix compiler):
examples/0140-types-named-const-array-dim.sx (s64 + string + struct elems)
examples/0141-types-slice-literal-direct-call-arg.sx (string + []s64)
Gate: zig build, zig build test, bash tests/run_examples.sh (387 passed).
Issues 0083 and 0084 marked RESOLVED.
43 lines
2.4 KiB
Markdown
43 lines
2.4 KiB
Markdown
# 0083 — fixed array with a named-constant dimension is miscompiled
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> **RESOLVED.** Root cause: `TypeResolver.resolveCompound`'s array arm resolved
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> the dimension with `if (length.data == .int_literal) ... else 0` — a named
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> const (`N :: 16`) hit the silent `else 0`, so `[N]T` became a 0-length / 0-byte
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> array and element access ran out of bounds (garbage for scalars, bus error for
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> slice/pointer/struct elements). Fix: the array arm now delegates the dimension
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> to `inner.resolveArrayLen` (symmetric with `inner.resolveInner` for the element
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> type). The stateful `Lowering.resolveArrayLen` evaluates the dimension as a
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> compile-time integer across the comptime-constant, generic-value, and
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> module-global const tables, and emits a diagnostic (no fabricated length) when
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> it isn't one. Files: `src/ir/type_resolver.zig`, `src/ir/lower.zig`,
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> `src/ir/type_bridge.zig`. Regression: `examples/0140-types-named-const-array-dim.sx`
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> (s64 + string + struct element types).
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## Symptom
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A fixed array whose dimension is a module-global integer constant (`N :: 16;
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a : [N]T`) miscompiles element access: reads/writes compute a wrong address.
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With `s64` elements `a[0]` returns GARBAGE (silent); with slice/pointer element
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types (`[N]string`) it Bus-errors. The identical program with a LITERAL dimension
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(`a : [16]T`) is correct. Silent-miscompile class (cf. 0079–0082).
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## Reproduction
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```sx
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#import "modules/std.sx";
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N :: 16;
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main :: () { a : [N]s64 = ---; a[0] = 7; print("a0={}\n", a[0]); }
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```
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`./zig-out/bin/sx run` prints `a0=8472789232` (garbage); want `a0=7`. Replacing
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`[N]` with `[16]` prints `7`.
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## Investigation prompt
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A fixed-array TYPE whose dimension is a named const (`N :: 16; [N]T`) resolves to
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a wrong element stride / array length in codegen — element address computation is
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wrong (garbage for scalars, bad pointer for slice/pointer elements). Literal
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dimensions are correct, so the defect is in resolving the array-type DIMENSION
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from a constant expression (vs a literal) — the dim likely resolves to 0/unknown
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or the element size is wrong. Look at array-type resolution where the length is a
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const-expr (type lowering / sizeof / element-stride computation). Fix so a
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named-const dimension yields the same layout as the literal. Verify with the
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repro (expect 7) + a `[N]string`/`[N]struct` case (no bus error, correct reads),
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and `zig build && zig build test && bash tests/run_examples.sh` green.
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