How to calculate gdp of a company during promotion and loss? Suppose a company is selling a good worthy of 200 dollars, but it was charging it for 100 dollars intending for promotion. And the company have to pay salaries of $200 per good, so it loses 100 dollars per good sold.

From the income side, it is 200 dollars to the employees and -100 dollars to the shareholders.

From the expenditure side, it's 100 dollars from the consumers.

Should the GDP be reckoned as 200 dollars as the good's market value or 100 dollars? And why?
As noted in a comment, GDP is associated with a country, not a firm.

But if we are talking about the contribution to GDP, the operating assumption is that calculations are based on observed (market) prices. So the value of consumption is \$100 if we are calculating GDP based on expenditures. If we are looking at domestic income, it would be \$100: \$200 wage income, and -\$100 business income. 

Statisticians do not attempt to decide what goods are “really worth”, they use data based on actual transactions. Since GDP numbers are estimates based on a variety of sources, it is unlikely that they capture when particular firms have promotional sales.