Investigate moving alpaka device code to .dev.cc files

[fwyzard]

The common approach for alpaka device code is to template all functions on the accelerator type:

template <typename TAcc>
ALPAKA_ACC_FN int sum(TAcc const& acc, int a, int b) { ... }

Another approach could be to move the code inside the ALPAKA_ACCELERATOR_NAMESPACE and use the accelerator type explicitly:

namespace ALPAKA_ACCELERATOR_NAMESPACE {
  ALPAKA_ACC_FN int sum(Acc1D const& acc, int a, int b) { ... }
}

This should let us move alpaka code that is not otherwise templated from header files to .dev.cc files.

Now that we start to have a sizeable alpaka-based code base, we should maybe re-evaluate both options.

[cmsbuild]

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[cmsbuild]

A new Issue was created by @fwyzard.

@Dr15Jones, @antoniovilela, @smuzaffar, @rappoccio, @makortel, @sextonkennedy can you please review it and eventually sign/assign? Thanks.

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[fwyzard]

assign heterogeneous

[cmsbuild]

New categories assigned: heterogeneous

@fwyzard,@makortel you have been requested to review this Pull request/Issue and eventually sign? Thanks

[makortel]

I agree the explicit Acc1D would be worth of exploring.

I'd further argue the Acc1D might be interesting option also when the function is otherwise templated, because the function (usually?) makes some assumption on the dimensionality of the Acc, and I'd assume the explicit Acc1D would ensure consistency between the function and the alpaka::exec() that calls the kernel calling the function.

[makortel]

Just to record, change from TAcc template argument to explicit Acc<N>D types is explored in #46916