[SLP][NFC]Fix a warning for comparison of integers of different signs.

Author: alexey-bataev

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -4346,9 +4346,10 @@ BoUpSLP::LoadsState BoUpSLP::canVectorizeLoads(
     // increases the cost.
     Loop *L = LI->getLoopFor(cast<LoadInst>(VL0)->getParent());
     bool ProfitableGatherPointers =
-        L && Sz > 2 && count_if(PointerOps, [L](Value *V) {
-                         return L->isLoopInvariant(V);
-                       }) <= Sz / 2;
+        L && Sz > 2 &&
+        static_cast<unsigned>(count_if(PointerOps, [L](Value *V) {
+          return L->isLoopInvariant(V);
+        })) <= Sz / 2;
     if (ProfitableGatherPointers || all_of(PointerOps, [IsSorted](Value *P) {
           auto *GEP = dyn_cast<GetElementPtrInst>(P);
           return (IsSorted && !GEP && doesNotNeedToBeScheduled(P)) ||