Rather than require `ArrayCopy` to create special versions of copy for
all arrays, use a precompiled versions. This should speed up compiles,
reduce the amount of code being generated, and require the device
compiler on fewer source files.
There are some cases where you still need to copy arrays that are not
well supported by the precompiled versions in `ArrayCopy`. (It will
always work, but the fallback is very slow.) In this case, you will want
to switch over to `ArrayCopyDevice`, which has the old behavior.
`vtkm::cont::UnknownArrayHandle` now provides a set of method that
allows you to copy data from one `UnknownArrayHandle` to another. The
first method, `DeepCopyFrom`, takes a source `UnknownArrayHandle` and
deep copies the data to the called one. If the `UnknownArrayHandle`
already points to a real `ArrayHandle`, the data is copied into that
`ArrayHandle`. If the `UnknownArrayHandle` does not point to an existing
`ArrayHandle`, then a new `ArrayHandleBasic` with the same value type as
the source is created and copied into.
The second method, `CopyShallowIfPossibleFrom` behaves similarly to
`DeepCopyFrom` except that it will perform a shallow copy if possible.
That is, if the target `UnknownArrayHandle` points to an `ArrayHandle`
of the same type as the source `UnknownArrayHandle`, then a shallow copy
occurs and the underlying `ArrayHandle` will point to the source. If the
types differ, then a deep copy is performed. If the target
`UnknownArrayHandle` does not point to an `ArrayHandle`, then the
behavior is the same as the `=` operator.
One of the intentions of these new methods is to allow you to copy
arrays without using a device compiler (e.g. `nvcc`). Calling
`ArrayCopy` requires you to include the `ArrayCopy.h` header file, and
that in turn requires device adapter algorithms. These methods insulate
you from these.
Added the following form of `ArrayCopy`:
```cpp
VTKM_CONT_EXPORT void ArrayCopy(
const vtkm::cont::UnknownArrayHandle& source,
const vtkm::cont::UnknownArrayHandle& destination);
```
Note that the destination array is a constant reference. This is
actually OK because you can change the contents of an
`UnknownArrayHandle` (as long as you don't change the array being
referenced). The main motivation for this change is to allow you to call
this form of `ArrayCopy` while passing in a `ArrayHandle` as the second
argument. C++ will automatically make the conversion, but the function
has to accept a const reference for it to be passed correctly.
Note that there is still a form of `ArrayCopy` that accepts a non-const
reference to the destination array. The two arrays behave the same
except for one difference. For the non-const version, if the
`UnknownArrayHandle` does not already point to an array (i.e. is not
valid), a new array will be created and placed in the destination
object. However, because this cannot be done for a const reference, an
exception is thrown instead.
The `ArrayCopy` was simply calling `IsOnDevice` to see if the array from
the `UnknownArrayHandle` was on a device. Seems right, but it is
actually operating on an `ArrayHandleRecombineVec`. This is a special
array that mostly behaves like other `ArrayHandle`s, but because it has
variable vec size, it breaks some `ArrayHandle` conventions.
One of the iffy things it has to do is stick the dependent `Buffer`
objects into the metadata of its own `Buffer` rather than list them in
the `Buffer` list. This means that `ArrayHandle` cannot properly check
them to see where they are located. Instead, it just sees that the one
`Buffer` it has is empty.
A recent change to `IsOnDevice` made it return true for any device if
the `Buffer` is empty. So previously this was broken in that it reported
that the array was not on any device. That changed to report that it was
on all devices, even inactive ones. So the code went from not
efficiently copying to throwing an exception.
This has been fixed by pulling one of the dependent arrays and checking
that one.
Rather than copy every type to every other type, only copy for the same
base type or copy to/from FloatDefault. This should reduce the amount of
code generated by a lot.
This reduces the size of the .o for ArrayCopy.cxx on my mac from
21MB to 7.7MB.
Add an overload of `ArrayCopy` that takes `UnknownArrayHandle`s and
copies them for (almost) any `ArrayHandle` type.
The code uses `CastAndCallWithExtractedArray` to reduce the total number
of copy conditions to about 100, which are all precompiled into the
library. On a debug build on my mac, this creates a .o file of 21MB.
That's not great, but not terrible. Hopefully, this can be used to
consolidate copy implementations elsewhere.
