Unbraced else whose body is a for-of over a generator, inside a loop: operand does not dominate this use #458

A for ... of over a generator, written as an unbraced else branch inside a loop, fails to compile in every memory model.

function* gen() {
    yield 1;
    yield 2;
}

function main() {
    for (let i = 0; i < 2; i++) {
        const it = gen();
        if (i == 0) it.next(); else for (const c of it) { print(c); }
    }
    print("done.");
}

tslang --emit=jit --no-default-lib -mm=gc (rc the same), main 8b9d631:

else_loop.ts:7:33: error: operand #0 does not dominate this use

These work and print 1, 2, done.:

• the same code with braces, if (i == 0) { it.next(); } else { for (const c of it) { print(c); } };
• an unbraced else for (const c of xs) over an array;
• an unbraced else for (let j = 0; ...).

So the failing combination is an unbraced else whose body is a for ... of over a generator, inside a loop.

Found by the final review of Shared<T> (own phase 8).

🤖 Generated with Claude Code