[SCEV] Split collecting and applying rewrite info from loop guards (NFC)

llvm/include/llvm/Analysis/ScalarEvolution.h

@@ -1299,8 +1299,26 @@ class ScalarEvolution {
   /// sharpen it.
   void setNoWrapFlags(SCEVAddRecExpr *AddRec, SCEV::NoWrapFlags Flags);
 
+  class LoopGuards {
+    DenseMap<const SCEV *, const SCEV *> RewriteMap;
+    bool PreserveNUW = false;
+    bool PreserveNSW = false;
+    ScalarEvolution &SE;
+
+    LoopGuards(ScalarEvolution &SE) : SE(SE) {}
+
+  public:
+    /// Collect rewrite map for loop guards for loop \p L, together with flags
+    /// indicating if NUW and NSW can be preserved during rewriting.
+    static LoopGuards collect(const Loop *L, ScalarEvolution &SE);
+
+    /// Try to apply the collected loop guards to \p Expr.
+    const SCEV *rewrite(const SCEV *Expr) const;
+  };
+
   /// Try to apply information from loop guards for \p L to \p Expr.
   const SCEV *applyLoopGuards(const SCEV *Expr, const Loop *L);
+  const SCEV *applyLoopGuards(const SCEV *Expr, const LoopGuards &Guards);
 
   /// Return true if the loop has no abnormal exits. That is, if the loop
   /// is not infinite, it must exit through an explicit edge in the CFG.