[llvm-dev] help me understand how nounwind attribute on functions works?

[Sanjoy Das via llvm-dev]

On Thu, Feb 9, 2017 at 8:41 AM, Reid Kleckner via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> On Wed, Feb 8, 2017 at 5:45 PM, Mehdi Amini <mehdi.amini at apple.com> wrote:
>>
>> What isn’t clear to me still is : why shouldn't this be transitive?
>> In the example you’re showing, for a caller of f() in bar, what is the
>> advantage of knowing that f() is nounwind if it an exception can still be
>> thrown? What does it allow?
>
>
> We know an exception cannot unwind out of f. An exception can be thrown
> inside something that f calls, but it must be caught before it unwinds
> beyond f.

So perhaps a viable rule is that every CallInst in a nounwind function
can be marked as nounwind (even though the callee for said CallInst
can't be)?

-- Sanjoy