[Bug c++/78484] New: if-else chain is not turned into a local jump table

["timshen at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78484

            Bug ID: 78484
           Summary: if-else chain is not turned into a local jump table
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: timshen at gcc dot gnu.org
  Target Milestone: ---

Convenient link: https://godbolt.org/g/AEYMwC

The following C++ code is slow, since it's not turned into a jump table:

template<int n>
void Foo();

template<int n>
struct BarImpl {
  static void Apply(int m) {
    if (m == n) {
      Foo<n>();
    } else {
      BarImpl<n-1>::Apply(m);
    }
  }
};

template<>
struct BarImpl<0> {
  static void Apply(int m) {
    Foo<0>();
  }
};

void Bar(int n) {
  BarImpl<30>::Apply(n);
}