Hello,
Now that I'm back to some C++ coding, I want to finish the integration of
viennacl::op_reduce<>.
I've noticed a lot of different operator overloads for
viennacl::scalar_expression<>, with basically different implicit
conversions to raw scalar. I'm a bit skeptical here :)
This allows to handle the (imho unpractical) cases such as :
cpu_scal = inner_prod(x1,x2)*5.0
or
cpu_scal = (vcl_scal1 + vcl_scal2)*5.0
I think that such expressions should be forbidden. I think that every
conversion involving host<->device data movement should be explicit, since
they trigger a flush of the scheduler's queue. Furthermore, we are heading
towards multi-devices computations, and these implicit conversions will
then become even more troublesome : an implicit inner_prod<->scalar
conversion would then need to sum the results obtained for each device...
Basically, I think that we should forbid any other implicit conversions
than the viennacl::scalar<T> <=> T one... Do you agree?
This would force to rewrite the examples above :
gpu_scal = (vcl_scal1 + vcl_scal2)*5.0;
cpu_scal = gpu_scal;
Which is I think more explicit and efficient than the previous approach :)
Philippe
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