Paying down debt and more R&D would be far better than stock buybacks.
Interestingly, due to the nature of the remaining debt, paying it down ahead of time vs stock buyback may amount to pretty much the same thing. Some of the long-term debt is in the form of
convertible warrants, which may be converted to stock at $8 per share, under certain agreed conditions. Currently the stock is at ~$86. So the effective fair value of these warrants is far higher than the principal amount of debt given on the balance sheet. I think AMD does account for the conversion of these warrants when projecting the number of shares outstanding going forward. For the accurate details, check out the annual report and company filings.
PS. Incidentally, AMD warns that these warrants ("2.125% Notes") may cause downwards pressure on the stock this quarter:
"The conversion of the 2.125% Notes may dilute the ownership interest of our existing stockholders, or may otherwise depress the price of our common stock. The conversion of some or all of the 2.125% Notes may dilute the ownership interests of our existing stockholders. The 2.125% Notes will mature on September 1, 2026, unless earlier redeemed or repurchased by us or converted. During the fourth calendar quarter of 2020, the sale price of our common stock for conversion was satisfied as of December 31, 2020 and as a result, the 2.125% Notes are eligible for conversion during the first calendar quarter of 2021. Any sales in the public market of our common stock issuable upon such conversion could adversely affect prevailing market prices of our common stock. In addition, the existence of the 2.125% Notes may encourage short selling by market participants because the conversion thereof could be used to satisfy short positions, or the anticipated conversion of the 2.125% Notes into cash and/or shares of our common stock could depress the price of our common stock."