private void initContextBitMasks(Register contextReg) {
		byte[] subMask = contextReg.getBaseMask();
		if (!contextReg.followsFlow()) {
			hasNonFlowingContext = true;
			for (int i = 0; i < nonFlowingContextRegisterMask.length; i++) {
				nonFlowingContextRegisterMask[i] |= subMask[i];
				flowingContextRegisterMask[i] &= ~subMask[i];
			}
		}
		else {
			for (int i = 0; i < flowingContextRegisterMask.length; i++) {
				flowingContextRegisterMask[i] |= subMask[i];
			}
			if (contextReg.hasChildren()) {
				for (Register childReg : contextReg.getChildRegisters()) {
					initContextBitMasks(childReg);
				}
			}
		}
	}
Set those bits in the nonFlowingContextRegisterMask which should not 
flow with context.
@param contextReg context register piece
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/util/AbstractProgramContext.java