[LoopVectorize] Fix for non-determinism in codegen

[mgrang]

Summary

This patch fixes issues in codegen uncovered due to https://reviews.llvm.org/D26718

[mssimpso]

LGTM!

lib/Transforms/Vectorize/LoopVectorize.cpp

if (Cmp && TheLoop->contains(Cmp) && Cmp->hasOneUse()) {
     Worklist.insert(Cmp);
     DEBUG(dbgs() << "LV: Found uniform instruction: " << *Cmp << "\n");
   }
 
   // Holds consecutive and consecutive-like pointers. Consecutive-like pointers
   // are pointers that are treated like consecutive pointers during
   // vectorization. The pointer operands of interleaved accesses are an
   // example.
-  SmallPtrSet<Instruction *, 8> ConsecutiveLikePtrs;
+  SmallSetVector<Instruction *, 8> ConsecutiveLikePtrs;
 
   // Holds pointer operands of instructions that are possibly non-uniform.
   SmallPtrSet<Instruction *, 8> PossibleNonUniformPtrs;
 
   // Iterate over the instructions in the loop, and collect all
   // consecutive-like pointer operands in ConsecutiveLikePtrs. If it's possible
   // that a consecutive-like pointer operand will be scalarized, we collect it
   // in PossibleNonUniformPtrs instead. We use two sets here because a single