[PATCH] D45015: [Preprocessor] Allow libc++ to detect when aligned allocation is unavailable.

[Eric Fiselier via Phabricator via cfe-commits]

EricWF added a comment.

In https://reviews.llvm.org/D45015#1123164, @ahatanak wrote:

> In https://reviews.llvm.org/D45015#1123097, @EricWF wrote:
>
> > In https://reviews.llvm.org/D45015#1121874, @ahatanak wrote:
> >
> > > I see, thank you.
> > >
> > > clang front-end currently fails to issue a warning or error when an aligned allocation/deallocation functions are required but not available in a few cases (e.g., delete called from a deleting destructor, calls to operator or builtin operator new/delete). I suppose those bugs should be fixed in separate patches.
> >
> >
> > I don't think we need to emit warnings from `__builtin_operator_new`/`__builtin_operator_delete`. Libc++ is the only consumer, and I think we can trust it to know what it's doing.
>
>
> Shouldn't clang warn when users explicitly call an aligned builtin operator new or delete in their code and the OS is too old to support the operator?
>
> For example:
>
>   typedef __SIZE_TYPE__ size_t;
>   namespace std {
>   enum class align_val_t : size_t {};
>   }
>  
>   int main() {
>     void *p = __builtin_operator_new(100, std::align_val_t(32));
>     return 0;
>   }
>


Yeah, I think you're right. Initially I thought `__builtin_operator_new` was documented as being intended for usage only in the STL, but it doesn't quite say that.
I have a patch which moves the checks into `DiagnoseUseOfDecl`, which should catch all of the cases we haven't already handled.


https://reviews.llvm.org/D45015