[Bug c++/62266] New: Loop unrolling with template metaprogramming not aggressive enough

[cand at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62266

            Bug ID: 62266
           Summary: Loop unrolling with template metaprogramming not
                    aggressive enough
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cand at gmx dot com

The following code fails to compile with all GCC versions I have, up to g++
(GCC) 5.0.0 20140817 (experimental). It also fails with clang, but it would be
nice for this to work, as it would save some writing.

The index i is in constant bounds, and so the compiler should be able to fully
unroll this loop into "foo<0>(); foo<1>(); foo<2>();".

#include <stdio.h>

template <int T> void foo() {
        printf("%u\n", T);
}

int main() {

        int i;
        for (i = 0; i < 3; i++) {
                foo<i>();
        }

        return 0;
}