[llvm-dev] returns_twice / noreturn

[Friedman, Eli via llvm-dev]

On 11/6/2017 7:07 AM, Serge Guelton via llvm-dev wrote:
> On Sun, Nov 05, 2017 at 09:22:47PM -0500, Yichao Yu via llvm-dev wrote:
>>> We do not implement that restricted semantics correctly either -- see
>>> https://bugs.llvm.org/show_bug.cgi?id=27190
>> Haha, I wondered for a minute whether I should bring up that bug...
>> We've seen pretty nasty crashes due to it and had to work around
>> it.....
>>
>> One of my recent work has also uncovered another (I believe) invalid
>> handling of returns_twice functions....
>> https://bugs.llvm.org/show_bug.cgi?id=35211
>> noalias returns seems to be treated as stack allocation but is not
>> required by either LangRef or C standard to be so for returns_twice
>> function handling....
> For the record, function returning twice are not even correctly
> annotated by glibc, see https://sourceware.org/bugzilla/show_bug.cgi?id=20382
>
> Looks like gcc handles that using a pattern matching approach
> (see https://gcc.gnu.org/ml/gcc-patches/2016-07/msg01163.html)
>
> Maybe we should do so too?

We already have code in clang to mark calls to setjmp/sigsetjmp/etc. 
returns_twice.

-Eli

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