[LoopPeel] Pass TripCount to computePeelCount by value instead of by reference. NFC

[craig.topper]

Summary

The TripCount is not modified by the function so it doesn't need
to be passed by reference. Verified by passing it as const reference
before changing to value.

[reames]

LGTM

This could have landed without review.

llvm/include/llvm/Transforms/Utils/LoopPeel.h

 gatherPeelingPreferences(Loop *L, ScalarEvolution &SE,
                          const TargetTransformInfo &TTI,
                          Optional<bool> UserAllowPeeling,
                          Optional<bool> UserAllowProfileBasedPeeling,
                          bool UnrollingSpecficValues = false);
 
 void computePeelCount(Loop *L, unsigned LoopSize,
                       TargetTransformInfo::PeelingPreferences &PP,
-                      unsigned &TripCount, DominatorTree &DT,
+                      unsigned TripCount, DominatorTree &DT,
                       ScalarEvolution &SE, unsigned Threshold = UINT_MAX);
 
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_UTILS_LOOPPEEL_H

llvm/lib/Transforms/Utils/LoopPeel.cpp

return any_of(ExitBlocks, [](const BasicBlock *EB) {
       return !EB->getTerminatingDeoptimizeCall();
     });
 }
 
 
 // Return the number of iterations we want to peel off.
 void llvm::computePeelCount(Loop *L, unsigned LoopSize,
                             TargetTransformInfo::PeelingPreferences &PP,
-                            unsigned &TripCount, DominatorTree &DT,
+                            unsigned TripCount, DominatorTree &DT,
                             ScalarEvolution &SE, unsigned Threshold) {
   assert(LoopSize > 0 && "Zero loop size is not allowed!");
   // Save the PP.PeelCount value set by the target in
   // TTI.getPeelingPreferences or by the flag -unroll-peel-count.
   unsigned TargetPeelCount = PP.PeelCount;
   PP.PeelCount = 0;
   if (!canPeel(L))
     return;