# issue 0155 — indexing a scalar pointer (`pc[0]`, `pc: *i64`) panics at LLVM emission

> **OPEN.** Found incidentally during an adversarial review of the fiber
> scheduler (a review probe used `pc[0]` on a `*i64`). NOT a fibers-stream
> blocker — the scheduler uses array-field indexing (`ctx.regs[i]`) and pointer
> deref (`p.*`), never scalar-pointer indexing — so it is filed for its own fix
> session, not fixed inline.

## Symptom

Indexing a pointer-to-scalar value with `[i]` crashes the compiler:

```
thread … panic: unresolved type reached LLVM emission — a type resolution
failure was not diagnosed/aborted
  src/backend/llvm/types.zig:196:28  toLLVMTypeInfo  (.unresolved arm)
  src/backend/llvm/types.zig:38      toLLVMType
  src/ir/emit_llvm.zig:2564          toLLVMType
```

Observed: compiler panic (no diagnostic). Expected: either lower `pc[i]` as
`*(pc + i)` (C semantics), or emit a clean diagnostic that a bare `*T` is not
indexable (deref with `.*`, or use a slice `[]T`). A `.unresolved` TypeId
reaching LLVM emission is unconditionally a compiler bug (a resolution failure
that was neither diagnosed nor aborted).

## Reproduction

```sx
#import "modules/std.sx";
main :: () -> i64 {
    x : i64 = 5;
    pc : *i64 = @x;
    return pc[0];   // panics the compiler
}
```

(repro: `issues/0155-scalar-pointer-index-llvm-panic.sx`)

## Investigation prompt

> The sx compiler panics ("unresolved type reached LLVM emission",
> `src/backend/llvm/types.zig:196`) when an index expression `pc[i]` is applied
> to a value of pointer-to-scalar type `*T` (repro:
> `issues/0155-scalar-pointer-index-llvm-panic.sx`). Trace `emitIndexGet`
> (`src/backend/llvm/ops.zig` ~1988) and the index-expr lowering in
> `src/ir/lower/` (the `.index_expr` arm): for a `*T` object, the element type
> resolves to `.unresolved` instead of `T`. Decide the intended semantics first
> (consult `specs.md` for whether a bare `*T` is indexable): if `pc[i]` should
> mean `*(pc + i)`, fix the index-expr type resolver to yield the pointee type
> `T` for a `*T` object (mirror the slice/array-pointer arm — see
> `ptrToArrayElem` / `getElementType` in `src/ir/lower/`), and verify codegen
> emits a GEP + load. If a bare `*T` is intentionally NOT indexable, emit a
> diagnostic at the lowering site ("cannot index `*T`; deref with `.*` or use a
> slice") and never let `.unresolved` reach emission. Verify: `sx run` the repro
> — expect either `5` (if indexable) or a clean compile error, never a panic.
> Then promote the repro to a regression test under `examples/`.