# 0061 — dead statements after `return` / `raise` emit into a closed block

> **✅ RESOLVED (2026-06-01).** Root cause: `lowerBlock` / `lowerBlockValue`
> ([src/ir/lower.zig](../src/ir/lower.zig)) broke their statement loop only on
> the `block_terminated` flag, which `lowerReturn` deliberately does NOT set (it
> would leak past an `if cond { return }` merge block — see the comment at
> `lowerReturn`). So a bare `return X;` / `raise` mid-block closed the current
> LLVM basic block while lowering kept emitting the trailing statements into it.
> Fix: after each `lowerStmt`, also stop the loop when
> `currentBlockHasTerminator()` is true (CFG-level termination of the *current*
> block — correctly false at an `if`/`inline if` merge block, so conditional
> returns still fall through). Regression test:
> [examples/0038-basic-dead-code-after-terminator.sx](../examples/0038-basic-dead-code-after-terminator.sx).

## Symptom

Any statement following a block-terminating statement (`return`, `raise`) at the
same block level is lowered into the basic block *after* its terminator, so the
LLVM verifier aborts:

```
LLVM verification failed: Terminator found in the middle of a basic block!
label %entry
```

Observed: a well-formed program with trailing dead code crashes the compiler.
Expected: the dead statements are dropped (unreachable); the program compiles
and runs.

This blocked ERR E5.1: the canonical failable-closure form from the plan,
`closure((x) -> (i32, !) { raise error.X; return x; })`, has a dead `return x;`
after the unconditional `raise` and tripped the verifier.

## Reproduction

Minimal (non-failable — the bug is general, not error-specific):

```sx
#import "modules/std.sx";
main :: () -> i32 { return 0; print("dead\n"); }
```

Failable facet (the form that blocked E5.1):

```sx
#import "modules/std.sx";
E :: error { Neg }
top :: (x: i64) -> (i64, !E) { raise error.Neg; return x; }
main :: () -> i32 { print("r={}\n", top(5) catch e 0); return 0; }
```

Both abort with "Terminator found in the middle of a basic block". A
*conditional* terminator (`if c { return 1; } return 2;`) was unaffected — its
merge block is fresh and has no terminator.

## Investigation prompt

The bug is in block-statement lowering in [src/ir/lower.zig](../src/ir/lower.zig):
`lowerBlock` (~line 1455) and `lowerBlockValue` (~line 1496) iterate `blk.stmts`
and only check the `block_terminated` flag. `lowerReturn` (~line 1767) emits a
`ret`/`br` terminator but intentionally does NOT set `block_terminated` (setting
it would leak past `if cond { return }` merge blocks and wrongly skip their
trailing statements — see the comment there). The fix is to stop the loop when
the *current* basic block has a terminator after lowering a statement, using the
existing `currentBlockHasTerminator()` helper (~line 11725), which is naturally
false at a merge block. Verify with both repros above (now compile + run) and
confirm `examples/0518-packs-pack-value-dispatch.sx` (inline-if + return +
trailing statements) still produces all its output.
