mirror of
https://github.com/vercel-labs/scriptc.git
synced 2026-10-28 06:53:42 +08:00
Malte Ubl
ec5adcfa18
Safe index reads of possibly-missing elements lower to lifted helpers (%arr.idxOr.N) that returned an owned element. Walks now admit required element reads of walked arrays (an index whose computation removes no edge), so these helpers qualify as borrowed returns: their body lends the element its array keeps alive (borrowing the optional read directly), and receivers consume the call's result without a retain/release pair, as for any borrowed-return call. Paged lookups such as `this.pages[id >> 8]?.[id & 255]` no longer retain the page array. Corpus 4630-4633 renumbered from 4620-4623 (checkerhot uses 4620/4621); 4634 pins paged lookups and a read followed by a removal.
120 lines
3.3 KiB
TypeScript
120 lines
3.3 KiB
TypeScript
// Field reads and rebound locals passed to borrowing callees: borrowed only
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// when neither the callee nor a later argument can replace them. Each
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// "replaces" case makes the field the value's last owner, frees it inside
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// the call, churns the allocator and then reads the argument again.
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class Name {
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text: string;
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parts: string[];
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constructor(text: string) {
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this.text = text;
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this.parts = text.split("");
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}
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}
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class Holder {
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name: Name | undefined;
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other: Name | undefined = undefined;
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items: Name[] = [];
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constructor(name: Name) {
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this.name = name;
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}
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}
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function churn(): number {
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let total = 0;
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for (let i = 0; i < 200; i++) total += new Name("churn-" + i).parts.length;
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return total;
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}
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function describe(n: Name | undefined): string {
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if (n === undefined) return "none";
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return n.text + ":" + n.parts.length;
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}
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// Writes an unrelated field: the caller may lend `h.name`.
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function touchOther(h: Holder, n: Name | undefined): string {
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h.other = new Name("other");
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churn();
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return describe(n);
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}
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// Replaces the very field the caller passed: the argument must be owned.
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function replaceName(h: Holder, n: Name | undefined): string {
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h.name = new Name("replacement");
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churn();
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return describe(n);
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}
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// Removes array elements: an element argument must be owned.
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function dropItems(h: Holder, n: Name): string {
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h.items.length = 0;
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churn();
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return describe(n);
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}
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function compose(a: string, b: string): string {
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return a + "|" + b;
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}
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function later(h: Holder): string {
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h.name = new Name("later");
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churn();
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return "later";
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}
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// A later argument replaces the field an earlier argument read.
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function laterArgument(h: Holder): string {
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return compose(describe2(h.name), later(h));
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}
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function describe2(n: Name | undefined): string {
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churn();
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return describe(n);
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}
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// A rebound parameter passed along: no callee can rebind the caller's local.
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function rebound(n: Name, h: Holder): string {
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if (n.text.length > 3) n = h.name ?? n;
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return replaceAndDescribe(n, h) + " " + describe(n);
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}
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function replaceAndDescribe(n: Name, h: Holder): string {
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h.name = undefined;
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churn();
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return describe(n);
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}
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// A constructor's stores into its own fresh object replace nothing the
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// caller lends; a constructor storing into another object does.
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class Attach {
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label: Name;
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constructor(h: Holder, label: Name) {
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h.name = undefined;
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churn();
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this.label = new Name("own-" + label.text);
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}
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}
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function construct(h: Holder): string {
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const a = new Attach(h, h.name!);
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return a.label.text;
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}
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const h1 = new Holder(new Name("first"));
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console.log(touchOther(h1, h1.name));
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const h2 = new Holder(new Name("second"));
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console.log(replaceName(h2, h2.name), describe(h2.name));
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const h3 = new Holder(new Name("third"));
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h3.items.push(new Name("item0"), new Name("item1"));
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console.log(dropItems(h3, h3.items[1]!));
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const h4 = new Holder(new Name("fourth"));
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console.log(laterArgument(h4), describe(h4.name));
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const h5 = new Holder(new Name("fifth-name"));
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console.log(rebound(new Name("sixth"), h5));
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const h6 = new Holder(new Name("seventh"));
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console.log(construct(h6), describe(h6.name));
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let sum = 0;
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for (let i = 0; i < 50; i++) {
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const h = new Holder(new Name("loop" + i));
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sum += touchOther(h, h.name).length + replaceName(h, h.name).length;
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}
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console.log("sum", sum);
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