[PATCH] D108905: [ItaniumCXXABI] Make __cxa_end_catch calls unconditionally nounwind

[Di Mo via Phabricator via cfe-commits]

modimo added a comment.

In D108905#2971861 <https://reviews.llvm.org/D108905#2971861>, @rjmccall wrote:

> I'm not really sure what the standard expects to happen if an exception destructor throws.  The standard tells us when the destruction happens — the latest point it can — but that clause doesn't mention exceptions from the destructor.  If there's a specific clause on this, I can't find it.  [except.throw]p7 says that "if the exception handling mechanism handling an uncaught exception directly invokes a function that exits via an exception, the function std::terminate is called", which is meant to cover exceptions thrown when initializing a catch variable.  Once the catch clause is entered, though, the exception is considered caught unless it's rethrown, so this clause doesn't apply when destroying the exception at the end of the clause.

Scanning through the standard this to me also looks like an overlooked corner case in the standard (TBF this is very corner case).

> If the catch variable's destructor throws, that seems to be specified to unwind normally (including destroying the exception, and if the destructor throws at that point then std::terminate gets called, as normal for exceptions during unwinding).

In this case, the destructor is throwing during normal scope exit so I don't think terminate behavior from [except.throw]p7 is enforced since we're not currently handling an uncaught exception. The handler is already active since we're past the initialization of the catch. Given that, I think this is akin to the example in [except.ctor]p2 and if the destructor is `noexcept(false)` should trigger a proper unwind like how an exception in the destructor of a simple automatic variable inside the handler scope would also do.


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