Reapply 105540, 105542, and 105548, and revert r105732.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106304 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ScalarEvolution.h

@@ -54,6 +54,10 @@ namespace llvm {
     /// The ScalarEvolution's BumpPtrAllocator holds the data.
     FoldingSetNodeIDRef FastID;
 
+    /// AllocationSequenceNumber - This is used as a deterministic tie
+    /// breaker when sorting SCEVs.
+    unsigned AllocationSequenceNumber;
+
     // The SCEV baseclass this node corresponds to
     const unsigned short SCEVType;
 
@@ -68,11 +72,18 @@ namespace llvm {
   protected:
     virtual ~SCEV();
   public:
-    explicit SCEV(const FoldingSetNodeIDRef ID, unsigned SCEVTy) :
-      FastID(ID), SCEVType(SCEVTy), SubclassData(0) {}
+    explicit SCEV(const FoldingSetNodeIDRef ID, unsigned num, unsigned SCEVTy) :
+      FastID(ID), AllocationSequenceNumber(num),
+      SCEVType(SCEVTy), SubclassData(0) {}
 
     unsigned getSCEVType() const { return SCEVType; }
 
+    /// getAllocationSequenceNumber - Return an arbitrary value which can be
+    /// used to deterministically order a sequence of SCEVs.
+    unsigned getAllocationSequenceNumber() const {
+      return AllocationSequenceNumber;
+    }
+
     /// Profile - FoldingSet support.
     void Profile(FoldingSetNodeID& ID) { ID = FastID; }
 
@@ -663,6 +674,7 @@ namespace llvm {
   private:
     FoldingSet<SCEV> UniqueSCEVs;
     BumpPtrAllocator SCEVAllocator;
+    unsigned CurAllocationSequenceNumber;
   };
 }