[SCEV][NFC] Replace redundant dyn_cast with cast in getAddExpr

[mkazantsev]

Summary

Replace dyn_cast which is ensured by isa just one line above with cast.

[reames]

LGTM

[sanjoy]

Btw, this would have been okay to land without pre-commit review.

llvm/trunk/lib/Analysis/ScalarEvolution.cpp

for (unsigned OtherIdx = Idx+1;
            cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()->getHeader(),
            AddRec->getLoop()->getHeader()) &&
         "AddRecExprs are not sorted in reverse dominance order?");
       if (AddRecLoop == cast<SCEVAddRecExpr>(Ops[OtherIdx])->getLoop()) {
         // Other + {A,+,B}<L> + {C,+,D}<L>  -->  Other + {A+C,+,B+D}<L>
         SmallVector<const SCEV *, 4> AddRecOps(AddRec->op_begin(),
                                                AddRec->op_end());
         for (; OtherIdx != Ops.size() && isa<SCEVAddRecExpr>(Ops[OtherIdx]);
-             ++OtherIdx)
-          if (const auto *OtherAddRec = dyn_cast<SCEVAddRecExpr>(Ops[OtherIdx]))
-            if (OtherAddRec->getLoop() == AddRecLoop) {
-              for (unsigned i = 0, e = OtherAddRec->getNumOperands();
-                   i != e; ++i) {
-                if (i >= AddRecOps.size()) {
-                  AddRecOps.append(OtherAddRec->op_begin()+i,
-                                   OtherAddRec->op_end());
-                  break;
-                }
-                SmallVector<const SCEV *, 2> TwoOps = {
-                    AddRecOps[i], OtherAddRec->getOperand(i)};
-                AddRecOps[i] = getAddExpr(TwoOps, SCEV::FlagAnyWrap, Depth + 1);
-              }
-              Ops.erase(Ops.begin() + OtherIdx); --OtherIdx;
-            }
+             ++OtherIdx) {
+          const auto *OtherAddRec = cast<SCEVAddRecExpr>(Ops[OtherIdx]);
+        }
         // Step size has changed, so we cannot guarantee no self-wraparound.
         Ops[Idx] = getAddRecExpr(AddRecOps, AddRecLoop, SCEV::FlagAnyWrap);
         return getAddExpr(Ops, SCEV::FlagAnyWrap, Depth + 1);
       }
     }
 
     // Otherwise couldn't fold anything into this recurrence.  Move onto the
     // next one.