Update IR

[jorgsowa]

IR commit: a4d13e263dd3010de06cd05235e006bfefa927a5

There are some fixes and improvements in IR implementation but I suppose only master can be targeted at this stage.

[jorgsowa]

@ndossche do you think it's safe to merge it on master? Are there any rules about the updating IR?

[ndossche]

There are both bugfixes and new features in IR.
On the one hand, merging only in master means that lower branches miss bugfixes. On the other hand, new features and IR code refactoring can cause regressions.
In the past, we always merged a new IR version into all branches.
In general, it's going to be hard to separate the bugfixes from feature additions, especially if they touch related code.
Or we should go into cherry-picking territory...

I'm not sure if any decision regarding this was made in my absence. cc @iluuu1994 @arnaud-lb

[iluuu1994]

We did briefly talk about this and I believe we landed on something more cautious. There were regressions introduced by IR in the past and it seems Dmitry is making many changes to it lately. So we'd prefer to only backport fixes when they are reported, and otherwise land the newest versions in master.

But it backporting is too tedious we can revise this strategy.