Add a LiveRangeEdit::Delegate protocol.

This will we used for keeping register allocator data structures up to date
while LiveRangeEdit is trimming live intervals.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127300 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/LiveRangeEdit.cpp

@@ -174,6 +174,8 @@ void LiveRangeEdit::eliminateDeadDefs(SmallVectorImpl<MachineInstr*> &Dead,
           ToShrink.insert(&LI);
       }
 
+      if (delegate_)
+        delegate_->LRE_WillEraseInstruction(MI);
       LIS.RemoveMachineInstrFromMaps(MI);
       MI->eraseFromParent();
     }