[Bug fortran/125914] -1.0**integer should be real(-1**integer)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125914

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Thomas Koenig <tkoenig@gcc.gnu.org>:

https://gcc.gnu.org/g:5b0da09f0ed5da80734c143d3ce2bacd78dc0c28

commit r17-1734-g5b0da09f0ed5da80734c143d3ce2bacd78dc0c28
Author: Thomas Koenig <tkoenig@gcc.gnu.org>
Date:   Mon Jun 22 07:26:25 2026 +0200

    Optimize (-1.0)**n to (real) (1 - ((n & 1) << 1)).

    The problem was that the optimization done for PR 57073 uses powi and
    friends, so it only applied to default integer exponent. The test
    case has an integer(kind=8) exponent, which is is calculated by
    calling a gfortran library function.

    There are two possible approaches: One would be to convert all
    integer types to default integer (because only the lowest-value
    bit matters to the result) and call the right __builtin_powi function.
    However, the generated code is suboptimal, see PR 125919.  I therefore
    chose the variant which currently generates the best code.

    This requires the change to the power_6.f90 test case.

    gcc/fortran/ChangeLog:

            PR fortran/125914
            * trans-expr.cc (gfc_conv_power_op): Rewrite (-1.0)**n into
            (real) (1 - ((n & 1) << 1)).

    gcc/testsuite/ChangeLog:

            PR fortran/125914
            * gfortran.dg/power_6.f90: Remove scans for powi.
            * gfortran.dg/power_10.f90: New test.