The existing implementation has three issues which this patch addresses.
1. The last dimension which represents the bytes in the type, has the
wrong stride and count. For example, for a 4 byte int, count=1 and
stride=4. The correct representation here is count=4 and stride=1
because there are 4 bytes (count=4) that we need to copy and we do not
skip any bytes (stride=1).
2. The size of the data copy was computed using the last dimension.
However, this is incorrect in cases where some of the final dimensions
get merged into one. In this case we need to take the combined size of
the merged dimensions, which is (Count * Stride) of the first merged
dimension.
3. The Offset into a dimension was computed as a multiple of its Stride.
However, this Stride which is in bytes, already includes the stride
multiplier given by the user. This means that when the user specified
1:3:2, i.e. elements 1, 3, 5, the runtime incorrectly copied elements 2,
4, 6. Fix this by precomputing at compile time the Offset to be in bytes
by correctly multiplying the offset by the stride of the dimension
without the user-specified multiplier.
In a nutshell, this moves our libomptarget code to populate the offload
subproject.
With this commit, users need to enable the new LLVM/Offload subproject
as a runtime in their cmake configuration.
No further changes are expected for downstream code.
Tests and other components still depend on OpenMP and have also not been
renamed. The results below are for a build in which OpenMP and Offload
are enabled runtimes. In addition to the pure `git mv`, we needed to
adjust some CMake files. Nothing is intended to change semantics.
```
ninja check-offload
```
Works with the X86 and AMDGPU offload tests
```
ninja check-openmp
```
Still works but doesn't build offload tests anymore.
```
ls install/lib
```
Shows all expected libraries, incl.
- `libomptarget.devicertl.a`
- `libomptarget-nvptx-sm_90.bc`
- `libomptarget.rtl.amdgpu.so` -> `libomptarget.rtl.amdgpu.so.18git`
- `libomptarget.so` -> `libomptarget.so.18git`
Fixes: https://github.com/llvm/llvm-project/issues/75124
---------
Co-authored-by: Saiyedul Islam <Saiyedul.Islam@amd.com>
