[libcxx-commits] [libcxxabi] Adding Separate OpenMP Offloading Backend to `libcxx/include/__algorithm/pstl_backends` (PR #66968)

[Louis Dionne via libcxx-commits]

================
@@ -466,6 +466,114 @@ Unpoisoning may not be an option, if (for example) you are not maintaining the a
 * You are using allocator, which does not call destructor during deallocation.
 * You are aware that memory allocated with an allocator may be accessed, even when unused by container.
 
+Offloading C++ Parallel Algorithms to GPUs
+------------------------------------------
+
+Experimental support for GPU offloading has been added to ``libc++``. The
+implementation uses OpenMP target offloading to leverage GPU compute resources.
+The OpenMP PSTL backend can target both NVIDIA and AMD GPUs.
+However, the implementation only supports contiguous iterators, such as 
+iterators for ``std::vector`` or ``std::array``.
+To enable the OpenMP offloading backend it must be selected with
+``LIBCXX_PSTL_BACKEND=openmp`` when installing ``libc++``. Further, when
+compiling a program, the user must specify the command line options
+``-fopenmp -fexperimental-library -stdlib=libc++``. To install LLVM with OpenMP
----------------
ldionne wrote:

```suggestion
``-fopenmp -fexperimental-library``. To install LLVM with OpenMP
```

It's implied that users are using libc++ if they are referring to this documentation. And since not all platforms require the use of `-stdlib=libc++`, I think we can drop this bit.

https://github.com/llvm/llvm-project/pull/66968