[SelectionDAG] Use UnknownSize for VP memory ops

In the style of D113888, this patch updates the various VP memory
operations (load, store, gather, scatter) to use UnknownSize. This is
for the same reason as for masked loads and stores: the number of
elements accessed is not generally known at compile time.

This is somewhat pessimistic in the sense that we may still find
un-canonicalized intrinsics featuring both an all-true mask and an EVL
equal to the vector size. Arguably those should be canonicalized before
the SelectionDAG, so those have been left for future work.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D115036

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -7331,20 +7331,12 @@ void SelectionDAGBuilder::visitVPLoadGather(const VPIntrinsic &VPIntrin, EVT VT,
   if (!IsGather) {
     // Do not serialize variable-length loads of constant memory with
     // anything.
-    MemoryLocation ML;
-    if (VT.isScalableVector())
-      ML = MemoryLocation::getAfter(PtrOperand);
-    else
-      ML = MemoryLocation(
-          PtrOperand,
-          LocationSize::precise(
-              DAG.getDataLayout().getTypeStoreSize(VPIntrin.getType())),
-          AAInfo);
+    MemoryLocation ML = MemoryLocation::getAfter(PtrOperand, AAInfo);
     AddToChain = !AA || !AA->pointsToConstantMemory(ML);
     SDValue InChain = AddToChain ? DAG.getRoot() : DAG.getEntryNode();
     MachineMemOperand *MMO = DAG.getMachineFunction().getMachineMemOperand(
         MachinePointerInfo(PtrOperand), MachineMemOperand::MOLoad,
-        VT.getStoreSize().getKnownMinSize(), *Alignment, AAInfo, Ranges);
+        MemoryLocation::UnknownSize, *Alignment, AAInfo, Ranges);
     LD = DAG.getLoadVP(VT, DL, InChain, OpValues[0], OpValues[1], OpValues[2],
                        MMO, false /*IsExpanding */);
   } else {
@@ -7395,7 +7387,7 @@ void SelectionDAGBuilder::visitVPStoreScatter(const VPIntrinsic &VPIntrin,
   if (!IsScatter) {
     MachineMemOperand *MMO = DAG.getMachineFunction().getMachineMemOperand(
         MachinePointerInfo(PtrOperand), MachineMemOperand::MOStore,
-        VT.getStoreSize().getKnownMinSize(), *Alignment, AAInfo);
+        MemoryLocation::UnknownSize, *Alignment, AAInfo);
     ST =
         DAG.getStoreVP(getMemoryRoot(), DL, OpValues[0], OpValues[1],
                        OpValues[2], OpValues[3], MMO, false /* IsTruncating */);