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Subject: [Bug target/97040] incorrect fused multiply add/subtract instruction
 generated from C code
Date: Wed, 09 Feb 2022 19:13:07 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97040

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jeff Law <law@gcc.gnu.org>:

https://gcc.gnu.org/g:eefec38c992e3622a69de9667e91f0cafbff03cc

commit r12-7145-geefec38c992e3622a69de9667e91f0cafbff03cc
Author: Jeff Law <jeffreyalaw@gmail.com>
Date:   Wed Feb 9 14:10:53 2022 -0500

    Avoid using predefined insn name for instruction with different semanti=
cs

    This isn't technically a regression, but it only impacts the v850 target
and
    fixes a long standing code correctness issue.

    As outlined in slightly more detail in the PR, the v850 is using the
pattern
    name "fnmasf4" and "fnmssf4" to generate fnmaf.s and fnmsf.s instructio=
ns
     respectively.

    Unfortunately fnmasf4 is expected to produce (-a * b) + c and
    fnmssf4 (-a * b) - c.  Those v850 instructions actually negate the enti=
re
    result.

    The fix is trivial.  Use a different pattern name so that the combiner =
can
    still generate those instructions, but prevent those instructions from
being
    used to implement GCC's notion of what fnmas and fnmss should be.

    This fixes pr97040 as well as a handful of testsuite failures for the v=
3e5
    multilib.

    gcc/
            PR target/97040
            * config/v850/v850.md (*v850_fnmasf4): Renamed from fnmasf4.
            (*v850_fnmssf4): Renamed from fnmssf4=