1 files changed, 5 insertions, 1 deletions
diff --git a/contrib/llvm-project/llvm/lib/Target/X86/X86ISelLowering.cpp b/contrib/llvm-project/llvm/lib/Target/X86/X86ISelLowering.cpp
index 682932b8f3e6..8bb7e81e19bb 100644
--- a/contrib/llvm-project/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/contrib/llvm-project/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -37558,7 +37558,11 @@ static SDValue combineX86ShuffleChain(ArrayRef<SDValue> Inputs, SDValue Root,
          (RootVT.is128BitVector() && Subtarget.hasVLX())) &&
         (MaskEltSizeInBits > 8 || Subtarget.hasBWI()) &&
         isSequentialOrUndefInRange(Mask, 0, NumMaskElts, 0, 2)) {
-      if (Depth == 0 && Root.getOpcode() == ISD::TRUNCATE)
+      // Bail if this was already a truncation or PACK node.
+      // We sometimes fail to match PACK if we demand known undef elements.
+      if (Depth == 0 && (Root.getOpcode() == ISD::TRUNCATE ||
+                         Root.getOpcode() == X86ISD::PACKSS ||
+                         Root.getOpcode() == X86ISD::PACKUS))
         return SDValue(); // Nothing to do!
       ShuffleSrcVT = MVT::getIntegerVT(MaskEltSizeInBits * 2);
       ShuffleSrcVT = MVT::getVectorVT(ShuffleSrcVT, NumMaskElts / 2);