[Bug 254911] lib/msun/ctrig_test fails if compiled with AVX (-mavx) or any CPUSET enabling AVX

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=254911

--- Comment #4 from commit-hook at FreeBSD.org ---
A commit in branch main references this bug:

URL:
https://cgit.FreeBSD.org/src/commit/?id=3b00222f156dca5700c839d73e36daf479fa640c

commit 3b00222f156dca5700c839d73e36daf479fa640c
Author:     Dimitry Andric <dim at FreeBSD.org>
AuthorDate: 2021-04-09 23:07:54 +0000
Commit:     Dimitry Andric <dim at FreeBSD.org>
CommitDate: 2021-04-10 11:59:57 +0000

    Avoid raising unexpected floating point exceptions in libm

    When using clang with x86_64 CPUs that support AVX, some floating point
    transformations may raise exceptions that would not have been raised by
    the original code. To avoid this, use the -fp-exception-behavior=maytrap
    flag, introduced in clang 10.0.0.

    In particular, this fixes a number of test failures with ctanhf(3) and
    ctanf(3), when libm is compiled with -mavx. An unexpected FE_INVALID
    exception is then raised, because clang emits vdivps instructions to
    perform certain divides. (The vdivps instruction operates on multiple
    single-precision float operands simultaneously, but the exceptions may
    be influenced by unused parts of the XMM registers. In this particular
    case, it was calculating 0 / 0, which results in FE_INVALID.)

    If -fp-exception-behavior=maytrap is specified however, clang uses
    vdivss instructions instead, which work on one operand, and should not
    raise unexpected exceptions.

    Reported by:    olivier
    Reviewed by:    arichardson
    PR:             254911
    MFC after:      1 week
    Differential Revision: https://reviews.freebsd.org/D29686

 lib/msun/Makefile | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

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