Exactly. I wouldn't start with the CPUID testing though. It's more like "Why do you care about ISA features"? Usually because you are trying to choose how man

Exactly. I wouldn't start with the CPUID testing though. It's more like "Why do you care about ISA features"? Usually because you are trying to choose how many code paths to support for runtime ISA-based dispatching, or how many binaries to build when you build multiple versions of a binary (which may include compile-time dispatching). So for that planning process, you only care about a few clumps. Then your CPUID testing strategy should still test all the required extensions, for completeness, and fall back as usual. Or something like that.