[Hexagon] Post-increment loads/stores enhancements

- Generate vector post-increment stores more aggressively.
- Predicate post-increment and vector stores in early if-conversion.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276800 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed