public Register getStackRegister() {
		if (stackReg != null) {
			return stackReg;
		}

		// figure out what register is used for return values, it must be assumed to be unknown upon return.
		stackReg = program.getCompilerSpec().getStackPointer();
		if (stackReg == null) {
			return null;
		}

		return stackReg;
	}
@return Register that represents the stack register
Ghidra/Features/Base/src/main/java/ghidra/program/util/VarnodeContext.java