RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.

We should backport this enhancement to benefit Clang:

commit 4997e8f31e7415652c3dedec672c0e9bf8caa9ca
Author: Adhemerval Zanella <adhemerval.zanella>
Date:   Fri Feb 1 10:39:57 2019 -0200

    math: Enable some math builtins for clang
    
    This patch enable the builtin usage for clang for the C99 functions
    fpclassify, isfinite, isnormal, isnan, isinf, and sigbit.  This allows
    clang optimize the calls on frontend instead of call the appropriate
    glibc symbols.
    
    Checked on aarch64-linux-gnu and x86_64-linux-gnu. I checked the supported
    version for each builtin based on released version from clang/llvm.
    
            * math/math.h (fpclassify, isfinite, isnormal, isnan): Use builtin for
            clang 2.8.
            (signbit): Use builtin for clang 3.3.
            (isinf): Use builtin for clang 3.7.

This should also be backported into Fedora 30+.

Verified, glibc uses __builtin versions of fpclassify signbit isfinite isnormal isnan isinf functions with clang.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2020:1828