Use std::unique instead of a SmallPtrSet to ensure unique instructions in UseSlots.

This allows us to always keep the smaller slot for an instruction which is what
we want when a register has early clobber defines.

Drop the UsingInstrs set and the UsingBlocks map. They are no longer needed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128886 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/SlotIndexes.h

@@ -178,6 +178,11 @@ namespace llvm {
       return getIndex() >= other.getIndex();
     }
 
+    /// isSameInstr - Return true if A and B refer to the same instruction.
+    static bool isSameInstr(SlotIndex A, SlotIndex B) {
+      return A.lie.getPointer() == B.lie.getPointer();
+    }
+
     /// Return the distance from this index to the given one.
     int distance(SlotIndex other) const {
       return other.getIndex() - getIndex();