Most - though not all! - of Jeremy Corbyn's supporters say that Corbyn didn't support the IRA. They say that he was simply “attempting to facilitate peace”. They don't really believe that, of course. Though to have a potential Prime Minister who out-rightly supported a terrorist organisation which blew dozens of civilians to pieces wouldn't really work - would it? (The IRA killed 115 people in England alone.) Thus they talk about Corbyn's role as a “peace maker”.
The fact is that Corbyn supported the IRA in every conceivable way; as did his communist friend (who's even more extreme than Corbyn) and Shadow Chancellor of the Exchequer - John “Mac the Knife” McDonnell. (John McDonnell is a fan of Chairman Mao. He also once believed that IRA terrorists should be honoured for their part in the “armed struggle” against Great Britain.)
For example, on the 27 November 1985, when talking about the Anglo-Irish Agreement (which gave the Irish government an advisory role in Northern Ireland's government), he explicitly said “those of us who wish to see a United Ireland oppose the agreement”. Thus not only was Corbyn not involved in any peace process. He was explicitly against it!
None of this is remotely surprising. The IRA was against what it and Corbyn called “British imperialism”. It also had very strong Marxist elements. These things alone titillated Corbyn's leftwing fancy.
Like the Socialist Workers Party (SWP) at the same time, Corbyn's position would have been one of “unconditional but critical support” for the IRA. (This position has also been applied to Hamas, Hezbollah, etc.) Though this position hardly makes sense. If support for Group X is “unconditional”, then it's hard to make any sense of it also being “critical”. If such support is unconditional, then even if you're critical, you'll still end up supporting the group you're criticising. Despite that, from Corbyn and the SWP there was no substantive criticism of the IRA anyway!
I suppose the phrase unconditional and uncritical support of the IRA would have been too much even for Corbyn to use. It would have made him sound like mere British tool of the IRA.
Despite all the above, Corbyn supporters say that we shouldn't go back to the 1980s in order to “discredit Corbyn”. They also say that the great thing about Corbyn is that he “sticks to his principles”. Yes; that's true. He's stuck to his principle since the 1970s. That must surely mean that he still believes exactly the same about the IRA in 2017 as he did in, say, 1985. Some would call that bone-headedness or ideological obsession. What's so wrong with changing one's positions in view of contradictory information or a moral/political reassessment?
In any case, it isn't of ultimate importance that Corbyn supported the IRA in the 1970s and 80s. It's that he would still support the IRA (or an equivalent group) today if the same situation were to arise. (Though, as a Prime Minister, things would no doubt be a little different.) After all, this man has supported Hamas, Hezbollah, Fidel Castro, Chairman Mao, the Soviet Union, and, if he's in tune with the group he once led (the Stop the War Coalition), he also supports/defends Iran's theocracy.
Thus Corbyn is certainly not a pacifist and he's certainly not against violence. The fact that communists/socialists like Corbyn slaughtered tens of millions of people in the 20th century may give the game away. What Corbyn is against is wars fought by “capitalist democracies”. What Corbyn is against is violence carried out by white right-wingers (though not by white Leftists). So not only is he not against violence and war, he's also a supreme hypocrite for pretending that he is!
Finally, let's face facts here. If Jeremy Corbyn MP were to still out-rightly support the IRA's former “struggle against British imperialism”, he wouldn't stand a chance in hell of being elected by the British people. That explains why (in 2017) he doesn't still out-rightly support the IRA. Instead, he obfuscates and he dissimulates about his former support of that terror group.