Now that DepType is private, we can start cleaning up some of its uses:

Now that DepType is private, we can start cleaning up some of its uses:
Document the Dirty value more precisely, use it for the uninitialized
DepResultTy value.  Change reverse mappings to be from an instruction*
instead of DepResultTy, and stop tracking other forms.  This makes it more
clear that we only care about the instruction cases.

Eliminate a DepResultTy,bool pair by using Dirty in the local case as well,
shrinking the map and simplifying the code.

This speeds up GVN by ~3% on 403.gcc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60232 91177308-0d34-0410-b5e6-96231b3b80d8