diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index dce05267267dd..72ad5ff70d446 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -36228,6 +36228,7 @@ static SDValue canonicalizeShuffleMaskWithHorizOp(
   // See if we can remove the shuffle by resorting the HOP chain so that
   // the HOP args are pre-shuffled.
   // TODO: Generalize to any sized/depth chain.
+  // TODO: Add support for 256/512-bit vectors.
   // TODO: Add support for PACKSS/PACKUS.
   if (isHoriz && NumEltsPerLane == 4 && VT0.is128BitVector() &&
       shouldUseHorizontalOp(Ops.size() == 1, DAG, Subtarget)) {