[llvm] [LoopVectorizer] Prune VFs based on plan register pressure (PR #132190)

[Luke Lau via llvm-commits]

================
@@ -7764,7 +7550,9 @@ VectorizationFactor LoopVectorizationPlanner::computeBestVF() {
   }
 
   for (auto &P : VPlans) {
-    for (ElementCount VF : P->vectorFactors()) {
+    SmallVector<ElementCount, 1> VFs(P->vectorFactors());
----------------
lukel97 wrote:

Are we expecting to only have one VF? Should we just let the template default choose the small size
```suggestion
    SmallVector<ElementCount> VFs(P->vectorFactors());
```

https://github.com/llvm/llvm-project/pull/132190