[SCEV] Fix wrong initialization of MaxNotTaken

[mkazantsev]

Summary

I'm not sure why, but since this code was introduced back in 2019, this
variable used wrong value to initialize. Somehow it just worked, but
needs to be fixed.

[fhahn]

LGTM, thanks! Surprising that the compiler didn't warn about the unused argument?

[mkazantsev]

Yeah, that's amazing.

llvm/include/llvm/Analysis/ScalarEvolution.h

struct ExitNotTakenInfo {
     const SCEV *MaxNotTaken;
     SmallPtrSet<const SCEVPredicate *, 4> Predicates;
 
     explicit ExitNotTakenInfo(PoisoningVH<BasicBlock> ExitingBlock,
                               const SCEV *ExactNotTaken,
                               const SCEV *MaxNotTaken,
                               const SmallPtrSet<const SCEVPredicate *, 4> &Predicates)
       : ExitingBlock(ExitingBlock), ExactNotTaken(ExactNotTaken),
-        MaxNotTaken(ExactNotTaken), Predicates(Predicates) {}
+        MaxNotTaken(MaxNotTaken), Predicates(Predicates) {}
 
     bool hasAlwaysTruePredicate() const {
       return Predicates.empty();
     }
   };
 
   /// Information about the backedge-taken count of a loop. This currently
   /// includes an exact count and a maximum count.