Fix invariant

[hhugo]

Effects

The effects pass was previously leaving unused blocks behind.

Inlining

The issue

I do not have a good grasp on what's is going on but it seems that a parent closure can sometimes be optimized before the closures it contains (recursive cycles).

function A () 
   fun B() {  A () }
   fun C() { B () }
   C();
}

• We first optimize A and decide nothing happens
• Then C and decide to inline B and B becomes dead
• We need to cleanup A but we already visited it

The fix

• We maintain a table for a closure to the block it is declared into.
• We collect the names of all inlined closures, filter out the one that are still live
• We map the dead closures to their block and rewrite theses blocks only.

[hhugo]

@vouillon, I think we need a comment explaining this line

[hhugo]

This invariant has been fixed in other PRs