[WIP] introduce a region unification table and use it in dropck

[arielb1]

Fixes#29844

I would prefer to
(a) make some performance measurements
(b) use the unification table in a few more places
before committing further, but this is probably good enough for beta.

r? @nikomatsakis

[nikomatsakis]

Why not just always resolve regions?

[nikomatsakis]

OK, so, re-reading your comment, I expect that you were probably shooting for a good way to make a kind of minimally invasive (and minimally risky) version of this PR, which makes a lot of sense.

[nikomatsakis]

I like this better than the alternative I proposed, and my main complaints about this PR was that it was not going as far as I would expect -- but that's probably good from the POV of being minimally invasive.
So:

@bors r+

[bors]

📌 Commit 80e191f has been approved by nikomatsakis

[nikomatsakis]

@bors p=1

[bors]

⌛ Testing commit 80e191f with merge d824ab1...

[bors]

💔 Test failed - auto-mac-64-opt

[alexcrichton]

@bors: retry

On Fri, Dec 11, 2015 at 11:38 PM, bors notifications@github.com wrote:

[image: 💔] Test failed - auto-mac-64-opt
http://buildbot.rust-lang.org/builders/auto-mac-64-opt/builds/7361

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#30242 (comment).

[bors]

⌛ Testing commit 80e191f with merge da31c14...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt

[arielb1]

@nikomatsakis

This commit causes a 50% regression in typeck performance (not the WIP). I will write a separate patch to fix it.

[pnkfelix]

I will write a separate patch to fix it.

Namely PR #30368 (right?)

[arielb1]

Right that was #30368