[Bug middle-end/57073] New: __builtin_powif (-1.0, k) should be optimized to "1.0 - 2.0 * (K%2)"

[burnus at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57073

             Bug #: 57073
           Summary: __builtin_powif (-1.0, k) should be optimized to "1.0
                    - 2.0 * (K%2)"
    Classification: Unclassified
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org


Motivated by PR57071.

In numerical code, it is not unlike to find code of the form "(-1.0) raised to
the power of k", in Fortran: (-1.0)**k.

That translates into:
  __builtin_powif (-1.0e+0, k)
which stays that way even with -O3.

Expected: It gets optimized to "1.0 - 2.0 * (K%2)"


Fortran test case:

real function f(k)
  integer, value :: k
  f = (-1.0)**k
end