Neither side can be declared an outright "winner" of the Iran-Iraq War. Both sides suffered heavy casualties and economic losses. The conflict is estimated to have cost over 1 million casualties and $1 trillion in damages. There were no major territorial changes as a result of the war.
While Iraq initially made some progress in invading Iran, the conflict eventually became a prolonged military deadlock. Neither side was able to achieve its strategic aims through military means, and the war ultimately ended in a ceasefire with the pre-war borders largely intact.
The real "winners," if any, were the Western powers and Gulf states that supported Iraq.
The West's profit
Firstly, the war helped Iran's Islamic revolution from spilling into other parts of the Middle East.
Secondly, the long and destructive war significantly weakened both Iran and Iraq militarily and economically, making them less of a threat to Western interests for years after the war ended. This created a broader power vacuum in the region that the West could exploit. The main downside for the West was Iraq's use of chemical weapons during the war, which the West turned a blind eye to in order to maintain Iraq's fragile balance against Iran's larger military.
Thirdly, the West sold large quantities of arms to both Iran and Iraq during the war, generating billions of dollars in revenue for Western arms companies. The United States in particular sold weapons to both sides throughout the conflict.
Fourthly, the West's support for Iraq during the war boosted its diplomatic influence in the Middle East. The United States in particular wielded more political clout through its backing of Baghdad.
Finally, the Soviet Union backed Iraq in the early stages of the war, but its influence declined as the conflict dragged on. The West saw the war as an opportunity to displace Soviet influence in both Iran and Iraq.
The GCC's profit
In addition to some common interests with the West, the oil-rich Gulf countries, especially Saudi Arabia and Kuwait, massively benefited from the Iran-Iraq war.
Firstly, with both Iran and Iraq's oil production disrupted by the war, the Gulf states were able to increase their own oil production and exports to make up for the shortfall. This resulted in higher oil revenues for them.
Secondly, Saudi Arabia and Kuwait were the biggest financial backers of Iraq during the war, providing hundreds of billions of dollars in loans, credit lines, and aid. This strengthened their political influence over Iraq. This actually resulted in the invasion of Kuwait afterward.