Added invariant field to the DAG.getLoad method and changed all calls.

Added invariant field to the DAG.getLoad method and changed all calls.

When this field is true it means that the load is from constant (runt-time or compile-time) and so can be hoisted from loops or moved around other memory accesses

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@144100 91177308-0d34-0410-b5e6-96231b3b80d8