[llvm] [VPlan] Add VPInstruction to unpack vector values to scalars. (PR #155670)

[Florian Hahn via llvm-commits]

================
@@ -1228,8 +1230,6 @@ bool VPInstruction::onlyFirstLaneUsed(const VPValue *Op) const {
     return getNumOperands() > 1;
   case VPInstruction::PtrAdd:
     return Op == getOperand(0) || vputils::onlyFirstLaneUsed(this);
-  case VPInstruction::WidePtrAdd:
-    return Op == getOperand(0);
----------------
fhahn wrote:

The current code here doesn't match the codegen for WidePtrAdd which is exposed by this patch; it only uses the first lane, if the pointer is a single scalar.

With this code, we would incorrectly insert an `unpack` and only provide the first lane instead of the vector pointers that is needed.

https://github.com/llvm/llvm-project/pull/155670