Known Limitations

This page documents current compiler bugs, codegen limitations, and workarounds.

Stage 1 (Frozen Compiler) Limitations

The frozen bootstrap compiler has several known issues:

Issue	Workaround
No generic class methods with receiver type inference	Use free functions or explicit type parameters
Float function parameters broken	Inline the computation instead
`%` modulo operator broken	Use `a - (a / b) * b`
Boolean variables broken	Use `var x = 0; x = 1; if x == 1 {`
`if/else if` chains broken	Use nested `if/else` blocks
`if not X` broken	Use `if X { return }` + fall-through
`.getTokenType()` cross-module issue	Use `checkToken(SeenTokenType.X)`

Recently Covered Regression Patterns

The current compiler source now has regression coverage for several patterns that were previously listed here as active production codegen bugs:

static fun in classes
class constructor struct literals
module-level var x = func()
module-level Array<T> / String initialization
functions returning Array<T> via r: syntax
let bindings of string expressions inside while loops
leading-brace string literals such as "{identifier"

Cold Compile Hang

Compilers built from the refactored source hang on 12 specific modules (0, 3, 5, 9, 10, 11, 12, 14, 16, 23, 25, 35) when compiling from scratch without IR cache.

Impact: Cannot cold-compile the full compiler with the refactored-source compiler.

Workaround: Use the pre-refactoring compiler (stored as stage1_frozen) to populate the IR cache. The safe_rebuild.sh script handles this automatically.

Note: This is NOT fork-related. The hang occurs with --no-fork as well.

Cross-Module GEP Bug

getelementptr %ClassName in module X fails if %ClassName is defined in module Y.

Workaround: Use memset zero-init instead of per-field GEP in isClassType() constructor path.

`extern fun __foo()` Rule

Names starting with __ with an empty body are skipped by codegen.

Workaround: Add explicit declare entry to ir_declarations.seen.

SSA Register Ordering

SSA registers must be strictly ascending. Pre-allocate the register for the FIRST instruction.

Array Invariant Loads

!invariant.load on array data pointers is incorrect -- data changes on push/resize. Do not mark array data as invariant.

Stack-Allocated SeenArray Headers

Do not stack-allocate SeenArray headers. Escaping pointers will crash. Always heap-allocate.

Runtime C Function Boolean Returns

Runtime C functions returning 0/1 int64_t for bool need trunc i64 to i1 in codegen.

Float `isNaN`/`isInfinite` Checks

Must NOT use fast flag (fast implies nnan/ninf).

HashMap Non-Determinism

HashMap iteration order is non-deterministic. In --deterministic mode, the compiler rejects HashMap usage unless marked with @nondeterministic.

Reporting Issues

If you encounter a new bug:

Create a minimal reproduction file (repro_*.seen)
Test with --emit-llvm to inspect generated IR
Use SEEN_TRACE_LLVM=all for detailed tracing
Report at github.com/codeyousef/SeenLang/issues