adapting a non-constexpr integral value to a non-type template parameter, and code bloat

Question

Consider a function object F taking a constexpr size_t argument I

struct F
{
    template 
    constex         


        

Answer 1

This is not exactly an answer and my question still stands, yet I have found a workaround that gives an impressive boost in compilation. It is a minor tweak of the solution given in the question, where parameter R is moved from operator() outside to structure idx, and the terminating condition now includes both R and N:

template <
    typename F, size_t L,
    size_t R = 1, size_t N = 0, bool = (R < 2 * L && N < L)
>
struct idx //...

The entire code is given in this new live example.

This approach apparently cuts down a huge number of unnecessary specialization combinations for R. Compile times and executable sizes drop dramatically. For instance, I have been able to compile in 10.7/18.7 seconds with Clang/GCC for L = 1<<12 (4096), yielding an executable of 220/239 KB. In this case, nm -C shows 546/250 versions of operator().