[libcxx-commits] [PATCH] D68269: [libc++] Define new/delete in libc++abi only by default

[Dimitry Andric via Phabricator via libcxx-commits]

dim added a subscriber: theraven.
dim added a comment.

In D68269#2322151 <https://reviews.llvm.org/D68269#2322151>, @ldionne wrote:

> Ping. Please take a look. I'll ship this in a week if nobody cares.

On FreeBSD we replaced (quite a while ago now) libsupc++ with libcxxrt.  Currently this also provides new and delete operators, but not all that are provided by libc++ (as of ~11.0.0 rc5):

libcxxrt:

  % nm -D /lib/libcxxrt.so.1|c++filt|grep -Ew 'new|delete' 
  0000000000017d10 W operator delete[](void*)
  0000000000017d30 W operator delete[](void*, unsigned long)
  0000000000017cc0 W operator delete(void*)
  0000000000017d20 W operator delete(void*, unsigned long)
  0000000000017cd0 W operator new[](unsigned long)
  0000000000017c20 W operator new(unsigned long)
  0000000000017c90 W operator new(unsigned long, std::nothrow_t const&)

libc++:

  00000000000b5c80 W operator delete[](void*)
  00000000000b5c90 W operator delete[](void*, std::nothrow_t const&)
  00000000000b5e10 W operator delete[](void*, std::align_val_t)
  00000000000b5e20 W operator delete[](void*, std::align_val_t, std::nothrow_t const&)
  00000000000b5ca0 W operator delete[](void*, unsigned long)
  00000000000b5e30 W operator delete[](void*, unsigned long, std::align_val_t)
  00000000000b5c50 W operator delete(void*)
  00000000000b5c60 W operator delete(void*, std::nothrow_t const&)
  00000000000b5de0 W operator delete(void*, std::align_val_t)
  00000000000b5df0 W operator delete(void*, std::align_val_t, std::nothrow_t const&)
  00000000000b5c70 W operator delete(void*, unsigned long)
  00000000000b5e00 W operator delete(void*, unsigned long, std::align_val_t)
  00000000000b5c10 W operator new[](unsigned long)
  00000000000b5c20 W operator new[](unsigned long, std::nothrow_t const&)
  00000000000b5da0 W operator new[](unsigned long, std::align_val_t)
  00000000000b5db0 W operator new[](unsigned long, std::align_val_t, std::nothrow_t const&)
  00000000000b5b70 W operator new(unsigned long)
  00000000000b5be0 W operator new(unsigned long, std::nothrow_t const&)
  00000000000b5cb0 W operator new(unsigned long, std::align_val_t)
  00000000000b5d70 W operator new(unsigned long, std::align_val_t, std::nothrow_t const&)

The libcxxrt implementations basically call malloc and free, and it has a comment:

  * These definitions are intended to be used for testing and are weak symbols
   * to allow them to be replaced by definitions from a STL implementation.
   * These versions simply wrap malloc() and free(), they do not provide a
   * C++-specific allocator.

but it seems that libc++ doesn't really have a substantially different implementation. (Not sure how you would generally implement a C++ specific allocator, but there will probably be cases where you can do things more efficiently if you know that you're not just allocating flat blobs.)

That said, both libcxxrt and libc++ mark their implementations as weak, so it's good guess which one wins... I'm actually not completely sure, except for the variants that libcxxrt doesn't implement. :)

In any case, we'd at least have to add the variants with `align_val_t` and with the const `nothrow_t` to libcxxrt, to make it backwards compatible.  Another option would be to switch to libc++abi, but that is quite a lot more work.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D68269/new/

https://reviews.llvm.org/D68269