swift234

ABCOpts: Add bounds check hoisting of induction identity accesses

We can now hoist the check in:

 for (i = start; i != end; ++i)
   a[i] = ...

or

 for i in start ..< end
   a[i] = ...

We will also hoist invariant checks as in

 k =
 for i in start ..< end
   a[k] = ...

We will also hoists the overflow check for "++i" out of the loop.

The only thing blocking vectorization of memset loops is the fact that we are
overflow checking the type size muliplication of array accesses. "a[i]" is
translated to "a + sizeof(T) * i" and this multiplication is still overflow
checked.

We can remove bounds checks in PrimeNum, XorLoop, Hash, MemSet, NBody, Walsh.

Memset                 ,  2371.00   ,  1180.00  ,  1179.00  ,        99.9%
XorLoop                ,  1403.00   ,  1255.00  ,  149.00   ,        11.9%

rdar://14757945

Swift SVN r21182