Revert "TargetLowering: fix an infinite DAG combine in SimplifySETCC"

This reverts commit b76c85b.

It broke the RISCV-enabled bots. Oops.

Author: jroelofs

llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp

@@ -4227,12 +4227,12 @@ SDValue TargetLowering::SimplifySetCC(EVT VT, SDValue N0, SDValue N1,
   bool N1ConstOrSplat =
       isConstOrConstSplat(N1, /*AllowUndefs*/ false, /*AllowTruncate*/ true);
 
-  // Canonicalize toward having the constant on the RHS.
+  // Ensure that the constant occurs on the RHS and fold constant comparisons.
   // TODO: Handle non-splat vector constants. All undef causes trouble.
   // FIXME: We can't yet fold constant scalable vector splats, so avoid an
   // infinite loop here when we encounter one.
   ISD::CondCode SwappedCC = ISD::getSetCCSwappedOperands(Cond);
-  if (N0ConstOrSplat && !N1ConstOrSplat && !OpVT.isScalableVector() &&
+  if (N0ConstOrSplat && (!OpVT.isScalableVector() || !N1ConstOrSplat) &&
       (DCI.isBeforeLegalizeOps() ||
        isCondCodeLegal(SwappedCC, N0.getSimpleValueType())))
     return DAG.getSetCC(dl, VT, N1, N0, SwappedCC);