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https://github.com/vercel-labs/scriptc.git
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Malte Ubl
622bacc914
`arr.length = n` always called scr_arr_set_len, even when n already is the length. tsc-ts resets three shared flow-cache arrays to their saved start after every flow walk, which is usually exactly that no-op. The emitted code now compares n with the current length first: equality is precisely the case the runtime accepts and leaves unchanged (-0 included, NaN never), so only real resizes and invalid lengths reach the runtime.
56 lines
1.7 KiB
TypeScript
56 lines
1.7 KiB
TypeScript
// Assigning an array's length: the unchanged length is a no-op, shorter
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// lengths release the removed elements, longer ones add holes, and invalid
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// lengths throw Node's RangeError. Reused work stacks reset this way in hot
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// loops (the checker's shared flow caches) must behave exactly like Node.
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class Node {
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id: number;
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constructor(id: number) {
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this.id = id;
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}
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}
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const stack: Node[] = [];
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const types: string[] = [];
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const flags: boolean[] = [];
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let checksum = 0;
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for (let round = 0; round < 200; round++) {
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const start = stack.length;
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for (let i = 0; i < round % 5; i++) {
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stack.push(new Node(round * 10 + i));
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types.push("t" + i);
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flags.push(i % 2 === 0);
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}
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for (const n of stack) checksum += n.id;
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// Reset to the recorded start: a no-op when nothing was pushed.
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stack.length = start + (round % 3 === 0 ? 0 : round % 5);
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types.length = stack.length;
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flags.length = stack.length;
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if (round % 7 === 0) {
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stack.length = 0;
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types.length = 0;
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flags.length = 0;
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}
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}
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console.log("work stack", stack.length, types.length, flags.length, checksum);
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const values = [new Node(1), new Node(2), new Node(3)];
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const kept = values[2]!;
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values.length = values.length;
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console.log("same", values.length, values[2] === kept);
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values.length = -0;
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console.log("negative zero", values.length, kept.id);
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values.length = 2;
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console.log("extend", values.length, 0 in values, 1 in values);
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values.length = 2.0;
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console.log("same float", values.length);
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for (const bad of [NaN, -1, 1.5, 2 ** 32, Infinity]) {
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try {
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values.length = bad;
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console.log("accepted", bad);
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} catch (error) {
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console.log("rejected", bad, (error as Error).name, (error as Error).message);
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}
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}
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console.log("after", values.length);
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