2 files changed, 8 insertions, 5 deletions
diff --git a/llvm/lib/Target/X86/Utils/X86ShuffleDecode.cpp b/llvm/lib/Target/X86/Utils/X86ShuffleDecode.cpp
index 9777c0d85e9..b1c69e779f3 100644
--- a/llvm/lib/Target/X86/Utils/X86ShuffleDecode.cpp
+++ b/llvm/lib/Target/X86/Utils/X86ShuffleDecode.cpp
@@ -255,15 +255,13 @@ void DecodeUNPCKLMask(MVT VT, SmallVectorImpl<int> &ShuffleMask) {
 
 void DecodeVPERM2X128Mask(MVT VT, unsigned Imm,
                           SmallVectorImpl<int> &ShuffleMask) {
-  if (Imm & 0x88)
-    return; // Not a shuffle
-
   unsigned HalfSize = VT.getVectorNumElements() / 2;
 
   for (unsigned l = 0; l != 2; ++l) {
-    unsigned HalfBegin = ((Imm >> (l * 4)) & 0x3) * HalfSize;
+    unsigned HalfMask = Imm >> (l * 4);
+    unsigned HalfBegin = (HalfMask & 0x3) * HalfSize;
     for (unsigned i = HalfBegin, e = HalfBegin + HalfSize; i != e; ++i)
-      ShuffleMask.push_back(i);
+      ShuffleMask.push_back(HalfMask & 8 ? SM_SentinelZero : i);
   }
 }
 
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index a92ab5ae2a0..5ad31b742a6 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -4390,6 +4390,7 @@ static SDValue getShuffleVectorZeroOrUndef(SDValue V2, unsigned Idx,
 /// IsUnary to true if only uses one source. Note that this will set IsUnary for
 /// shuffles which use a single input multiple times, and in those cases it will
 /// adjust the mask to only have indices within that single input.
+/// FIXME: Add support for Decode*Mask functions that return SM_SentinelZero.
 static bool getTargetShuffleMask(SDNode *N, MVT VT,
                                  SmallVectorImpl<int> &Mask, bool &IsUnary) {
   unsigned NumElems = VT.getVectorNumElements();
@@ -4519,6 +4520,10 @@ static bool getTargetShuffleMask(SDNode *N, MVT VT,
     ImmN = N->getOperand(N->getNumOperands()-1);
     DecodeVPERM2X128Mask(VT, cast<ConstantSDNode>(ImmN)->getZExtValue(), Mask);
     if (Mask.empty()) return false;
+    // Mask only contains negative index if an element is zero.
+    if (std::any_of(Mask.begin(), Mask.end(), 
+                    [](int M){ return M == SM_SentinelZero; }))
+      return false;
     break;
   case X86ISD::MOVSLDUP:
     DecodeMOVSLDUPMask(VT, Mask);