Buybacks specifically have been on a torrid pace and are helping provide a floor to a market that for much of 2018 had looked tired and volatile after a 20 percent S&P 500 gain the year before. Repurchases are up 83 percent year to date, far ahead of the 9 percent gain in dividends, while M&A activity involving U.S. companies has surged 130 percent, according to UBS.
The Nasdaq, which is heavily weighted to tech, is up about 9.5 percent year to date, easily topping the other major averages. Led by Apple's $100 billion, announced buybacks have jumped $160 billion in 2018, an increase of more than 200 percent from 2017.
Health-care shares, however, have lagged and are up less than 1 percent year to date.
Tracing corporate flow
Source: CompuStat, FactSet, Bloomberg, Dealogic, UBS
UBS estimates that the combination of buybacks, dividends and demand flows account for some 40 percent in performance this year. The S&P 500 has nudged 2.6 percent higher and the Dow industrials are just ahead of breakeven.
The market, however, is coming off its best month since January and the best May since 2009, according to Bank of America Merrill Lynch. The gains came amid a big liquidity surge and improving economic fundamentals. Barclays researchers last week said recent economic performance is indicating "the arrival of fiscal stimulus" through the tax cuts and increased spending.
In addition to skewing toward tech, buybacks also have been heavily tilted toward growth stocks, which have seen $280 billion in activity, compared with value's $90 billion. That is "providing further fuel for potential outperformance as the growth/value debate heats up," Parker said.
Large-cap growth stocks are up 7.4 percent year to date while value has fallen 3.2 percent, according to FactSet.
In addition, the biggest companies were the biggest repurchasers, with the top 20 percent of firms by market cap accounting for 72 percent of buybacks in the first quarter.
The patterns have been big determinants in market action, Parker wrote.
"The largest and most profitable firms have continued to repurchase shares, which investors have used to cover shorts and further increase exposure to momentum and growth, particularly those firms with positive sales growth/revisions," the strategist said.
May was a particularly active month for repurchases, with a record $171.3 billion in announcements, spurred by Apple, according to market data firm TrimTabs.
— CNBC's John Schoen contributed.WATCH: Trump tax cut lifts dividends to new record