https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85216
--- Comment #12 from Timothy Pearson <tpearson at raptorengineering dot com> --- After quite a bit of investigation, this is down to the Spectre v2 user mode protections on POWER9, which (from what I understand) involve completely disabling the branch predictor. My question then comes down to, why wasn't the retpoline style mitigation used on ppc64el? Nuking hardware elements seems extreme and is obviously causing serious problems for direct branching code (like that being seen here). What would be involved in creating a retpoline-type mitigation for ppc64el, so that we can run with the branch predictor turned back on (already verified to fix much of the performance issues seen on POWER9)?
