Re: [PATCH] Add __attribute__((malloc) to allocator and remove unused code

[Jonathan Wakely <jwakely at redhat dot com>]

On 17/05/18 12:54 +0200, Marc Glisse wrote:
> On Mon, 14 May 2018, Jonathan Wakely wrote:
>
> > As discussed at https://gcc.gnu.org/ml/libstdc++/2018-01/msg00073.html
> > we can simplify the allocator function for valarray memory. I also
> > noticed that the _Array(size_t) constructor is never used.
> >
> > 	* include/bits/valarray_array.h (__valarray_get_memory): Remove.
> > 	(__valarray_get_storage): Call operator new directly. Remove ignored
> > 	top-level restrict qualifier and add malloc attribute instead.
>
> I am trying to understand the point of adding this attribute. The 
> function is just
>
> { return static_cast<_Tp*>(operator new(__n * sizeof(_Tp))); }
>
> The idea is that it isn't safe (? see PR 23383) to mark operator new 
> with the attribute, but it is safe for this particular use?

I'd forgotten about that (I was assuming the compiler doesn't need to
be told about the properties of operator new, because they're defined
by the language). We can remove the attribute.


> When optimizing, I certainly hope this trivial function gets inlined, 
> and then the attribute is lost (should the inliner add 'restrict' when 
> inlining a function with attribute malloc?) and all that matters is 
> operator new.