swift234

Add initial support for eliminating nontrivial dead objects.

This currently handles fixed size dead arrays, which speeds up Richards (and DeadArray)
by 100x:
Fixes <rdar://problem/20980377> Add dead array elimination to DeadObjectElimination

To handle arrays, I added a run of DeadObjectElimination before high
level semantic inlining. This is necessary to recognize array
initialization. Recognizing low-level operations on the array would
require more extensive analysis with interprocedural escape
information.

Arrays are actually the hard case. To handle the general (easy) case,
I just need to add a simple destructor analysis.

This also makes the order that instructions are removed deterministic.

Swift SVN r29168