The template interpreter contains branch-free conversion code for T_BOOLEAN (TemplateInterpreterGenerator::generate_result_handler_for).

SharedRuntime::generate_native_wrapper uses unoptimized code to "Unpack the native result" for T_BOOLEAN.

Power10 has the "setbc" / "setbcr" instruction.

We could create a new function for the conversion and use "setbc" on Power10 (determined by VM_Version::has_brw()) and otherwise the branch-free implementation. We should have a function for 32 and one for 64 bit operations (or one with supports both).
The new code for MacroAssembler::verify_secondary_supers_table should also use the new function.