[PATCH] D133341: [C++] [Coroutines] Prefer aligned (de)allocation for coroutines - implement the option2 of P2014R0

[Yuanfang Chen via Phabricator via cfe-commits]

ychen accepted this revision.
ychen added a comment.
This revision is now accepted and ready to land.

LGTM. Give it a few days in case @rjmccall have comments.



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Comment at: clang/test/SemaCXX/coroutine-alloc-4.cpp:49
+    void return_value(int) {}
+    void *operator new(std::size_t, std::align_val_t) noexcept;
+    void *operator new(std::size_t) noexcept;
----------------
ChuanqiXu wrote:
> ychen wrote:
> > ChuanqiXu wrote:
> > > ychen wrote:
> > > > Like this test case, please add additional test cases to check the expected look-up order, one test for each consecutive pair should be good.
> > > > 
> > > > ```
> > > > void* T::operator new  ( std::size_t count, std::align_val_t al, user-defined-args... );
> > > > void* T::operator new  ( std::size_t count, std::align_val_t al);
> > > > void* T::operator new  ( std::size_t count, user-defined-args... );
> > > > void* T::operator new  ( std::size_t count);
> > > > void* operator new  ( std::size_t count, std::align_val_t al );
> > > > ```
> > > > 
> > > > 
> > > Yeah, I'm testing this in CodeGenCoroutines. (It is hard to test the selection in Sema Test)
> > Thanks for adding the overload. I think the `noexcept` on operator new is not necessary. Strictly speaking, it is not a conforming API.
> The noexcept here is necessary. The specs says the allocation function should have a noexcept specifier if get_return_object_on_allocation_failure presents.
I see. I didn't realize that, before P2014, the way class-specific operator new/delete are looked up is already different between coroutine and regular routine. Basically, with the normal operator new/delete lookup rules, the no-throw and potentially-throw allocation functions may overload, so the throw function type must have `std::throw_t` parameter; with the coroutine operator new/delete lookup rules, the no-throw and potentially-throw allocation functions do not overload since `get_return_object_on_allocation_failure` is either found or not found, thus the `std::throw_t` parameter is not necessary for the potentially-throw allocation function.



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