[DAGCombine] Poison-prove scalarizeExtractedVectorLoad.

extractelement is poison if the index is out-of-bounds, so just
scalarizing the load may introduce an out-of-bounds load, which is UB.

To avoid introducing new UB, we can mask the index so it only contains
valid indices.

Fixes PR50382.

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D103077

1 files changed, 2 insertions, 9 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 0838e52..5146f0d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -18411,26 +18411,19 @@ SDValue DAGCombiner::scalarizeExtractedVectorLoad(SDNode *EVE, EVT InVecVT,
 
   Alignment = NewAlign;
 
-  SDValue NewPtr = OriginalLoad->getBasePtr();
-  SDValue Offset;
-  EVT PtrType = NewPtr.getValueType();
   MachinePointerInfo MPI;
   SDLoc DL(EVE);
   if (auto *ConstEltNo = dyn_cast<ConstantSDNode>(EltNo)) {
     int Elt = ConstEltNo->getZExtValue();
     unsigned PtrOff = VecEltVT.getSizeInBits() * Elt / 8;
-    Offset = DAG.getConstant(PtrOff, DL, PtrType);
     MPI = OriginalLoad->getPointerInfo().getWithOffset(PtrOff);
   } else {
-    Offset = DAG.getZExtOrTrunc(EltNo, DL, PtrType);
-    Offset = DAG.getNode(
-        ISD::MUL, DL, PtrType, Offset,
-        DAG.getConstant(VecEltVT.getStoreSize(), DL, PtrType));
     // Discard the pointer info except the address space because the memory
     // operand can't represent this new access since the offset is variable.
     MPI = MachinePointerInfo(OriginalLoad->getPointerInfo().getAddrSpace());
   }
-  NewPtr = DAG.getMemBasePlusOffset(NewPtr, Offset, DL);
+  SDValue NewPtr = TLI.getVectorElementPointer(DAG, OriginalLoad->getBasePtr(),
+                                               InVecVT, EltNo);
 
   // The replacement we need to do here is a little tricky: we need to
   // replace an extractelement of a load with a load.