[SCEV] Fix issues found during the review of r251283. NFC.

[sbaranga]

Summary

Replace (const SCEVAddRecExpr *) with cast<SCEVAddRecExpr>.

Rename SCEVApplyRewriter to SCEVLoopAddRecRewriter (which is a more
appropriate name) since the description is "takes a scalar evolution
expression and applies the Map (Loop -> SCEV) to all AddRecExprs."

llvm/trunk/include/llvm/Analysis/ScalarEvolutionExpressions.h

namespace llvm {
 
   private:
     ValueToValueMap ⤅
     bool InterpretConsts;
   };
 
   typedef DenseMap<const Loop*, const SCEV*> LoopToScevMapT;
 
-  /// The SCEVApplyRewriter takes a scalar evolution expression and applies
+  /// The SCEVLoopAddRecRewriter takes a scalar evolution expression and applies
   /// the Map (Loop -> SCEV) to all AddRecExprs.
-  class SCEVApplyRewriter : public SCEVRewriteVisitor<SCEVApplyRewriter> {
+  class SCEVLoopAddRecRewriter
+      : public SCEVRewriteVisitor<SCEVLoopAddRecRewriter> {
   public:
     static const SCEV *rewrite(const SCEV *Scev, LoopToScevMapT &Map,
                                ScalarEvolution &SE) {
-      SCEVApplyRewriter Rewriter(SE, Map);
+      SCEVLoopAddRecRewriter Rewriter(SE, Map);
       return Rewriter.visit(Scev);
     }
 
-    SCEVApplyRewriter(ScalarEvolution &SE, LoopToScevMapT &M)
+    SCEVLoopAddRecRewriter(ScalarEvolution &SE, LoopToScevMapT &M)
         : SCEVRewriteVisitor(SE), Map(M) {}
 
     const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
       SmallVector<const SCEV *, 2> Operands;
       for (int i = 0, e = Expr->getNumOperands(); i < e; ++i)
         Operands.push_back(visit(Expr->getOperand(i)));
 
       const Loop *L = Expr->getLoop();
       const SCEV *Res = SE.getAddRecExpr(Operands, L, Expr->getNoWrapFlags());
 
       if (0 == Map.count(L))
         return Res;
 
-      const SCEVAddRecExpr *Rec = (const SCEVAddRecExpr *) Res;
+      const SCEVAddRecExpr *Rec = cast<SCEVAddRecExpr>(Res);
       return Rec->evaluateAtIteration(Map[L], SE);
     }
 
   private:
     LoopToScevMapT &Map;
   };
 
 /// Applies the Map (Loop -> SCEV) to the given Scev.
 static inline const SCEV *apply(const SCEV *Scev, LoopToScevMapT &Map,
                                 ScalarEvolution &SE) {
-  return SCEVApplyRewriter::rewrite(Scev, Map, SE);
+  return SCEVLoopAddRecRewriter::rewrite(Scev, Map, SE);
 }
 
 }
 
 #endif