@Override
	public int getInstructionLength(OperandValue ov) {
		Constructor cons = ov.getConstructor();
		OperandSymbol sym = cons.getOperand(ov.getIndex());
		PatternExpression patexp = sym.getDefiningExpression();
		if (patexp == null) {
			return 0;
		}
		int length = solver.getInstructionLength(patexp);
		int shamt = AssemblyTreeResolver.computeOffset(sym, cons);
		return length + shamt;
	}
Obtains the "defining expression"

<p>
This is either the symbol's assigned defining expression, or the expression associated with
its defining symbol.

@return the defining expression, or null if neither is available
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/assembler/sleigh/expr/OperandValueSolver.java