https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85216
--- Comment #9 from Bill Schmidt <wschmidt at gcc dot gnu.org> --- You mentioned you're on a POWER9 machine. It could be that you have firmware with Spectre mitigations applied, which will affect all indirect branches. It may be that you do not have Spectre mitigations applied on your x86 machine, in which case the comparison would be expected to be quite different. Depending on firmware levels, the mitigations may be able to be switched off, so you should check into that first. PHP is known to be sensitive to indirect branch performance. The Power landing page for these mitigations is https://www.ibm.com/blogs/psirt/potential-impact-processors-power-family/. >From here you should be able to get to further information for your specific hardware and OS version.