private void lockFunctionSignatureLines() {

		ClangLine leftLine = getClangLine(leftLines, 0);
		ClangLine rightLine = getClangLine(rightLines, 0);

		// If we can find both lines with function signatures then lock lines on them.
		ClangLine leftFunctionLine = findFunctionSignatureLine(leftLines);
		ClangLine rightFunctionLine = findFunctionSignatureLine(rightLines);
		if (leftFunctionLine != null && rightFunctionLine != null) {
			leftLine = leftFunctionLine;
			rightLine = rightFunctionLine;
		}

		if (leftLine != null && rightLine != null) {
			setLockedLineNumbers(leftLine.getLineNumber(), rightLine.getLineNumber());
			lockLines(BigInteger.valueOf(lockedLeftLineNumber),
				BigInteger.valueOf(lockedRightLineNumber));
		}
	}
Clears the existing line number pairing
Ghidra/Features/CodeCompare/src/main/java/ghidra/features/codecompare/decompile/CodeDiffFieldPanelCoordinator.java