[DAG] Fold multiple insert_vector_elt of zero values into an AND mask

This also allows us to make use of the existing isVectorClearMaskLegal shuffle canonicalization

Differential Revision: https://reviews.llvm.org/D145939

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -20982,6 +20982,20 @@ SDValue DAGCombiner::visitINSERT_VECTOR_ELT(SDNode *N) {
             return NewShuffle;
       }
 
+      // If all insertions are zero value, try to convert to AND mask.
+      // TODO: Do this for -1 with OR mask?
+      if (!LegalOperations && llvm::isNullConstant(InVal) &&
+          all_of(Ops, [InVal](SDValue Op) { return !Op || Op == InVal; }) &&
+          count_if(Ops, [InVal](SDValue Op) { return Op == InVal; }) >= 2) {
+        SDValue Zero = DAG.getConstant(0, DL, MaxEltVT);
+        SDValue AllOnes = DAG.getAllOnesConstant(DL, MaxEltVT);
+        SmallVector<SDValue, 8> Mask(NumElts);
+        for (unsigned I = 0; I != NumElts; ++I)
+          Mask[I] = Ops[I] ? Zero : AllOnes;
+        return DAG.getNode(ISD::AND, DL, VT, CurVec,
+                           DAG.getBuildVector(VT, DL, Mask));
+      }
+
       // Failed to find a match in the chain - bail.
       break;
     }