Credit Suisse and Canaccord Genuity joined a growing list of top Wall Street banks that have raised their 2018 outlooks for U.S. equity markets before the year has even started.

The two echoed peers in citing the Republican tax bill in adjusting their S&P 500 targets higher, with a reduced corporate tax rate expected to buoy earnings for scores of the nation's largest companies more than they expected when hatching their initial 2018 outlooks.

"It's really simple: For the last six months, I've said that my 2,800 target for the S&P target is too low because you had to implement the tax cuts," Canaccord's Tony Dwyer said on CNBC's "Halftime Report" Thursday. "Corporate credit's going to be put to work in buybacks, it's going to be put to work in M&A activity. You've got equity-friendly things in the background on top of this tax cut."

Now the biggest bull on Wall Street, Dwyer adjusted his target to 3,100, implying 15 percent upside for the stock market over the next 12 months. The financial and energy sectors should be the "biggest beneficiaries" of the lower corporate rate, added Dwyer, with earnings set to pop 18.5 percent and 21.3 percent, respectively.

The flood of optimism on equities comes even as the S&P notches daily records: The index closed at an all-time high Monday and fell just short of beating that record Thursday, up more than 20 percent this year. For its part, the Dow Jones industrial average has closed at a record high 70 times this year, the most record closes in a single calendar year. The index added 55 points Thursday.

Jonathan Golub of Credit Suisse also tweaked his models Thursday, writing to clients that "corporate results have surprised, GDP expectations have improved, and tax rates have fallen."

He revised his S&P target to 3,000 while matching Dwyer's earnings per share estimate at $155. Noting that corporations may already have had tax cuts "baked in" to their business strategy, Golub explained that he sees the market's advance coming from underlying profit growth and "modest" multiple expansion.

"In the first half of the year, I think clearly the economy's going to be better and I think the question investors are now asking is how much of an extra kicker do we get on the economy," he told CNBC on Wednesday. "If you look at the tech sector, there's no indication that the sector is showing signs of weakness."

The strategist's comments on technology stem from the sector's remarkable climb over the past 12 months. Though pundits were worried that the Trump administration would take a chillier tone on Silicon Valley, large-cap technology has easily led the market in 2017 with names like Facebook and Amazon dominating financial headlines each earnings season. The S&P sector is up 38 percent since January.