[ASDAlexander77]

Fixes #457. Fixes #456.

On Windows, a try whose scope cleans up on the way out lost its exception whenever the function also allocated on the stack dynamically, as a two-argument print does. The cleanup comes from an owning let (its release) or a using. For example, let t = s; print("in try", t.v); throw 1; terminated with 0x80000003 instead of running the catch. This happened in every model, under JIT and AOT. A let whose initializer throws (#456) is the same cleanup and failed the same way.

Cause

Win32ExceptionPass turned the cleanup's exit into a cleanupret to a new catch-all funclet that rethrew (_CxxThrowException(null, null)), and that funclet unwound to the real handler. With a dynamic alloca in the function, the handler never caught the rethrow. Two hand edits of the LLVM IR settled it:

• cleanupret unwind label <handler>, clang's shape: fixed it.
• The rethrow kept, but as an invoke to the handler: did not fix it.

Fix

A cleanup with a handler to go on to now unwinds straight to it, and the invokes inside the cleanup unwind there too. The catch-all funclet is still built for a cleanup with no handler in the function, which unwinds to the caller; otherwise it is left unreachable. Linux is untouched.

Tests

• New test: 00try_cleanup_then_catch.ts, registered as compile and JIT tests and in the rc/none corpus. It terminated before the change. It covers:
  • an owning let and a two-argument print in the try;
  • a two-argument print in the catch;
  • a using with a two-argument print in the catch;
  • a let whose initializer throws, and one whose cast throws (A let in try whose initializer throws is not caught (stack overflow / uncaught exception) #456);
  • a const as the control.
• Original repros: every repro from A let in try whose initializer throws is not caught (stack overflow / uncaught exception) #456 and A throw in a try that declares a class-typed let is not caught (crash in every model) #457 now runs under gc and rc.
• Full Release ctest: 3666/3667. The one failure is test-compile-gc-defaultlib-collector, the known local LNK2005 against the stale installed default library, which fails on main the same way. The existing EH tests all pass: 00try_*, nested catch, using in a catch.

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