For each region, we create a metadata node. Then when an instruction is
added to the Region, it gets tagged with the metadata node for that
region. In the following example, we have a Region that contains only
the `%t0` instruction.
```
define i8 @foo(i8 %v0, i8 %v1) {
%t0 = add i8 %v0, 1, !sbvec !0
%t1 = add i8 %t0, %v1
ret i8 %t1
}
!0 = distinct !{!"region"}
```
This commit also adds a function to create regions from metadata already
present in a Function.
This metadata can be used for debugging: if we dump IR before a Region
pass, the IR will contain enough info to re-create the Region and run
the pass by itself in a later invocation.
---------
Co-authored-by: Alina Sbirlea <alina.g.simion@gmail.com>
3bb92b530f