device_reference not stripped before passing values to placeholder actors in some cases

[smitsyn]

I've faced a bug that I believe is caused by thrust::device_reference<T> in some cases not being stripped to T before being passed to function objects that are composed using placeholders (actors?). The minimal example I could come up with:

#include <thrust/device_vector.h>
#include <thrust/inner_product.h>
#include <thrust/functional.h>

void foo()
{
    using namespace thrust::placeholders;

    thrust::device_vector<float> v1, v2;

    thrust::inner_product(v1.begin(), v1.end(), v2.begin()
        , 0.0f, thrust::plus<float>{}, _1 + 1.0f);
}

Here, the problem is related to the last argument (BinaryOp2). The same can be demonstrated with this function object:

struct erroneous_thing
{
    template <typename T>
    __host__ __device__
        T operator()(const T& lhs, const T& rhs) const {
        return lhs + rhs;
    }
};
//...........
    thrust::inner_product(v1.begin(), v1.end(), v2.begin()
        , 0.0f, thrust::plus<float>{}, erroneous_thing{});

Somehow erroneous_thing is instantiated with T being thrust::device_reference<float>, while it should be float, resulting in a compile error. I haven't faced the problem with any other algorithm I've used; thrust::transform properly strips reference, as well as reduction part of inner_product (e.g. passing erroneous_thing{} as a first parameter is fine).

CUDA toolkit 10.2.

[alliepiper]

Compiler Explorer link: https://www.godbolt.org/z/-8gpEp