/System/Library/Frameworks/Metal.framework/Versions/A/XPCServices/MTLCompilerService.xpc/Contents/MacOS/MTLCompilerService MTLCompilerService compiles a machine-agnostic version of Metal (Apple's shader language for 3D rendering on their GPUs) into GPU code that runs on the specific GPU in your device, with the current graphics settings.
The binary is a part of Metal public framework.