[ASDAlexander77]

Ray tracer performance (item 5): two compiler changes, and a Windows EH crash on main that the second one exposed.

Changes

1. A closure copies a parameter nothing assigns (5b5d5cc). A captured parameter used to be moved into a heap cell shared by the frame and the closure's box, so getNaturalColor made six cells per call for addLight. A parameter that neither the body nor a closure in it assigns (++/-- now count as assignments) is captured by copy, as this and a const already were.
   • -mm=own: a closure that does not escape borrows the copy, generalizing spec 70's this rule (isBorrowableCapture: a parameter's read, or a copy the enclosing closure's box holds). Generator parameters, callbacks and Shared<T> handles stay in cells. An escaping closure over a parameter's copy is still refused with the old "its value is the caller's" message.
   • As a side effect, a nested non-escaping closure capturing an outer closure's const copy now compiles under own; it was an error on main.
2. Windows EH: an inlined throw in a catch-all that ends in resume keeps its funclet bundle (2dab213). This was already broken on main: a using whose disposal is a direct call (a @final class) and throws crashed with --opt, because MLIR's inliner put the throw inside the catch funclet with no "funclet" bundle. 00using_dispose_throws (callerCatches, bothThrow) caught it once change 3 made dispose calls direct.
3. A call through a vtable to a method no class overrides is a direct call (06328f4). After the module is generated, every class it made is known. A method that no class overrides, in a class that nothing outside the module can extend, gets ThisSymbolRef instead of ThisVirtualSymbolRef, as a @final receiver already does. "Nothing outside can extend" means the class is not exported, declared, imported or a C++ binding, and is not a base of such a class.

Ray tracer

Median of 7 runs, ms; every build prints the same checksum, and neither benchmark source changed.

Build	main	params by copy	+ direct calls	vs Rust idiomatic (55)
gc	266	97	79	1.4x
rc	171	133	120	2.2x
none	157	96	79	1.4x
own	143	104	86	1.6x

Testing

• ctest 6534/6534 (Windows Release).
• Fuzz seeds 79000-80599 clean.
• DefaultLib lib.ts compiles under own, rc, gc and none.
• New tests:
  • own/own_param_capture_copies (all four models);
  • tests/00class_method_devirtualized: overrides declared after the call, two classes down, generic and function-local subclasses, and abstract methods;
  • class-method-devirtualized.cmake: an IR check of which calls are direct. It fails on main's compiler.
• Not verified locally: Linux. The EH fix is Windows-only, but the same inlined-throw shape exists on Linux through linuxCleanupCatches. Read 00using_dispose_throws and 00class_method_devirtualized first on the Linux CI.

Known

• Under own, an inner closure escaping from an outer closure is still an error, but its message changed from "it is captured from an enclosing function" to "borrows a field".
• Left for a follow-up: Intersection | null (README variant B, about 16 ms). Its null test compares the type tag as a string, so fixing it means changing how null is stored in a union.

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