Bypass Slow Divides

* Only apply divide bypass optimization when not optimizing for size. 
* Fixed bug caused by constant for 0 value of type Int32,
  used dividend type to generate the constant instead.
* For atom x86-64 apply the divide bypass to use 16-bit divides instead of
  64-bit divides when operand values are small enough.
* Added lit tests for 64-bit divide bypass.

Patch by Tyler Nowicki!




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176442 91177308-0d34-0410-b5e6-96231b3b80d8