[llvm] [SandboxVec][BottomUpVec] Implement pack of scalars (PR #115549)

[Sriraman Tallam via llvm-commits]

================
@@ -164,7 +164,39 @@ void BottomUpVec::tryEraseDeadInstrs() {
   DeadInstrCandidates.clear();
 }
 
-Value *BottomUpVec::vectorizeRec(ArrayRef<Value *> Bndl) {
+Value *BottomUpVec::createPack(ArrayRef<Value *> ToPack) {
+  BasicBlock::iterator WhereIt = getInsertPointAfterInstrs(ToPack);
+
+  Type *ScalarTy = VecUtils::getCommonScalarType(ToPack);
+  unsigned Lanes = VecUtils::getNumLanes(ToPack);
----------------
tmsri wrote:

Since all values in this bundle have the same scalar type, isn't it just more efficient to do:

```
  unsigned Lanes = VecUtils::getNumLanes(Utils::getExpectedType(ToPack[0]))  * ToPack.size();
```

https://github.com/llvm/llvm-project/pull/115549