self_tail_call.js
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self_tail_call.js
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	// Test self-tail-call optimization in JIT
	// Without the optimization, deep recursion blows the native stack.

	// 1. Simple countdown — verifies correctness + no stack overflow
	function countdown(n) {
	if (n <= 0) return 0;
	return countdown(n - 1);
	}

	// 2. Accumulator pattern — tail-recursive sum
	function sum(n, acc) {
	if (n <= 0) return acc;
	return sum(n - 1, acc + n);
	}

	// 3. Mutual-arg swap (ensures args are copied correctly, not aliased)
	function gcd(a, b) {
	if (b === 0) return a;
	return gcd(b, a % b);
	}

	// 4. Deep recursion that would stack-overflow without TCO
	const DEEP = 1_000_000;

	console.time("countdown 1M");
	const r1 = countdown(DEEP);
	console.timeEnd("countdown 1M");
	console.log("countdown:", r1);

	console.time("sum 1M");
	const r2 = sum(DEEP, 0);
	console.timeEnd("sum 1M");
	console.log("sum:", r2);

	console.time("gcd");
	const r3 = gcd(1071, 462);
	console.timeEnd("gcd");
	console.log("gcd(1071,462):", r3);

	// 5. Stress: 10M iterations to measure loop vs call overhead
	console.time("countdown 10M");
	countdown(10_000_000);
	console.timeEnd("countdown 10M");

	// 6. Closure-based self-tail-call (upval self-reference)
	const fib_tail = function f(n, a, b) {
	if (n <= 0) return a;
	return f(n - 1, b, a + b);
	};

	console.time("fib_tail 100");
	const r4 = fib_tail(100, 0, 1);
	console.timeEnd("fib_tail 100");
	console.log("fib_tail(100):", r4);

	console.time("fib_tail 1M");
	const r5 = fib_tail(1_000_000, 0, 1);
	console.timeEnd("fib_tail 1M");
	console.log("fib_tail(1M):", typeof r5 === "number" ? "ok" : "FAIL");