At both large tech companies where I worked (about 16 years as an engineer and then about 5 years as a first level manager), the process was essentially the same.
The company would first go to a third party which would collect compensation information from a lot of tech companies. The company would provide it's compensation information for various job titles (Engineering technician, Engineer I, Engineer II, Project Manager I, etc.), and would also pay for the aggregated and anonymized data.
The company could then, in theory, decide on their overall compensation strategy. At both companies, the strategy seemed to be to pay about average, get about average, but assert that their employees were the best. So if the average compensation went up by 5% in the survey, they would allocate 5% of total wages to their raise pool.
That 5% total was allocated differently, though, depending on rated performance and managerial discretion (the latter especially in terms of equity compensation and borderline cases). Typically the top "cream of the crop" employees were given outsized raises - 12% to 20%, the latter usually if a person's performance was unusually high relative to their current salary. The next level - the well above average but not superstar - would be perhaps 7% to 11%. The average would get inflation-level raises, so 4% to 6%. Below average would get 0% and encouraged to try harder, or be in the process of being managed out of the company.
So you can actually reverse engineer what the company (and somewhat your immediate manager) thinks of you by looking at your raises and compare them with the overall raise pool (if you know it) or wage inflation generally (as a generally decent proxy). If you're not getting raises or your raises are below average, then you're a below average employee or are working for a company that is struggling economically (like a newspaper company in the last decade). About inflation? You're in the wide middle average. Well above average? You're above average and the company wants you to stay. Amazingly generous? You're top of the pile and/or somehow were underpaid when you first started.
Another tell is equity compensation. Stock options, RSUs, and the like were typically only given to managers and the top two tiers of employee performers. A great amount went to managers, a large chunk went to the cream of the crop, and a decent to modest chunk to the above average folks. Average and below got zero equity compensation at both places (above and beyond token amounts like "every employee is being issued options for 50 shares").