On Thu, 17 May 2018, Richard Biener wrote:
On Thu, May 17, 2018 at 1:14 PM Marc Glisse <marc.gli...@inria.fr> wrote:
On Thu, 17 May 2018, Jonathan Wakely wrote:
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.
I am not necessarily asking to remove it. I don't have a good
understanding of what would break if we marked operator new with the
attribute, so I have no idea if those reasons also apply for this use in
valarray.
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.
If we determine that using the attribute here but not on operator new is
the right choice, then I believe we need some middle-end tweaks so it
isn't ignored.
We don't have a good way to do this. Your suggestion of adding restrict
would work if it were not that only function-scope restrict uses are later
handled...
This seems extremely similar to the issue of inlining functions with
restrict arguments.
I have written a PR, but it is probably not worth submitting.
--
Marc Glisse
