Add `EndRegion` statement kind to MIR.

 * Emit `EndRegion` for every code-extent for which we observe a
   borrow. To do this, we needed to thread source info back through
   to `fn in_scope`, which makes this commit a bit more painful than
   one might have expected.

 * There is `end_region` emission in `Builder::pop_scope` and in
   `Builder::exit_scope`; the first handles falling out of a scope
   normally, the second handles e.g. `break`.

 * Remove `EndRegion` statements during the erase_regions mir
   transformation.

 * Preallocate the terminator block, and throw an `Unreachable` marker
   on it from the outset. Then overwrite that Terminator as necessary
   on demand.

 * Instead of marking the scope as needs_cleanup after seeing a
   borrow, just treat every scope in the chain as being part of the
   diverge_block (after any *one* of them has separately signalled
   that it needs cleanup, e.g. due to having a destructor to run).

 * Allow for resume terminators to be patched when looking up drop flags.

   (In particular, `MirPatch::new` has an explicit code path,
   presumably previously unreachable, that patches up such resume
   terminators.)

 * Make `Scope` implement `Debug` trait.

 * Expanded a stray comment: we do not emit StorageDead on diverging
   paths, but that end behavior might not be desirable.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/librustc/ich/impls_mir.rs b/src/librustc/ich/impls_mir.rs
index ae2bea3027d..cb017b7f886 100644
--- a/src/librustc/ich/impls_mir.rs
+++ b/src/librustc/ich/impls_mir.rs
@@ -226,6 +226,9 @@ for mir::StatementKind<'tcx> {
             mir::StatementKind::StorageDead(ref lvalue) => {
                 lvalue.hash_stable(hcx, hasher);
             }
+            mir::StatementKind::EndRegion(ref extents) => {
+                extents.hash_stable(hcx, hasher);
+            }
             mir::StatementKind::Nop => {}
             mir::StatementKind::InlineAsm { ref asm, ref outputs, ref inputs } => {
                 asm.hash_stable(hcx, hasher);