[SLP][NFCI] Don't trim indexes, reuse a variable (#149074)

Author: pfusik

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -8622,11 +8622,10 @@ void BoUpSLP::tryToVectorizeGatheredLoads(
                                State == LoadsState::CompressVectorize)
                              return false;
                            ConsecutiveNodesSize += VL.size();
-                           unsigned Start = std::distance(Slice.begin(), It);
-                           unsigned Sz = Slice.size() - Start;
+                           size_t Start = std::distance(Slice.begin(), It);
+                           size_t Sz = Slice.size() - Start;
                            return Sz < VL.size() ||
-                                  Slice.slice(std::distance(Slice.begin(), It),
-                                              VL.size()) != VL;
+                                  Slice.slice(Start, VL.size()) != VL;
                          }))
                 continue;
               // Try to build long masked gather loads.