@csgordon
It's probably because of this: https://en.wikipedia.org/wiki/Standard_Portable_Intermediate_Representation#LLVM-based_versions
It's some sort of intermediate code for graphics command stream — the features that your graphics card supports are executed on hardware directly, the ones that your hardware does not support are translated in real time and done in software.
This allows for semi-decent performance even on very old hardware because at least some of it gets hardware-accelerated.