[NFC] Fix a compiler warning

[xiaoqing_wu]

Summary

Fix a warning caused by -Wrange-loop-analysis

[kazu]

May I ask which cpp file you see the warning in? I just built clang and llvm, but I wasn't able to reproduce the warning. Thanks!

[xiaoqing_wu]

It shows up in those source files that include SetOperations.h, for example: llvm/lib/CodeGen/MachineLoopInfo.cpp.

We found that this warning showed up in certain versions of clang, but not in some other versions. Since this is a legit warning, we thought it's better to fix it.

llvm/include/llvm/ADT/SetOperations.h

 }
 
 /// set_is_subset(A, B) - Return true iff A in B
 ///
 template <class S1Ty, class S2Ty>
 bool set_is_subset(const S1Ty &S1, const S2Ty &S2) {
   if (S1.size() > S2.size())
     return false;
-  for (const auto &It : S1)
+  for (const auto It : S1)
     if (!S2.count(It))
       return false;
   return true;
 }
 
 /// set_is_strict_subset(A, B) - Return true iff A in B and and A != B
 ///
 template <class S1Ty, class S2Ty>