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.
### Issue: Dimension override missing
When variable count expressions were used with stride, the constant
subsection path computed size first. This marked `ArgSizes` with byte
size semantics. Variable expression logic later triggered, but reused
`ArgSizes` assuming "bytes" semantics
`OMPIRBuilder.cpp` didn't handle dimension count for
`OMP_MAP_NON_CONTIG` flag
**Result**: `ArgSizes` wasn't overwritten with dimension count, breaking
non-contiguous mapping.
**Fixes**:
`llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp` - Expression semantics for
non-contiguous.
stride/count.
Generate 3D descriptor structures with runtime dimensions.
Fix dimension override to use dimension count instead of byte size.
Added testcases to cover stack arrays, heap pointers, struct members,
etc.
