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llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

static SDValue truncateVectorWithNARROW(unsigned Opcode, EVT DstVT, SDValue In,
   if (!isPowerOf2_32(NumElems))
     return SDValue();
   assert(DstVT.getVectorNumElements() == NumElems && "Illegal truncation");
   assert(SrcSizeInBits > DstVT.getSizeInBits() && "Illegal truncation");
 
   LLVMContext &Ctx = *DAG.getContext();
   EVT PackedSVT = EVT::getIntegerVT(Ctx, SrcVT.getScalarSizeInBits() / 2);
 
-  // Pack to the largest type possible:
-  // vXi64/vXi32 -> PACK*SDW and vXi16 -> PACK*SWB.
+  // Narrow to the largest type possible:
+  // vXi64/vXi32 -> i16x8.narrow_i32x4_u and vXi16 -> i8x16.narrow_i16x8_u.
   EVT InVT = MVT::i16, OutVT = MVT::i8;
   if (SrcVT.getScalarSizeInBits() > 16) {
     InVT = MVT::i32;
     OutVT = MVT::i16;
   }
   unsigned SubSizeInBits = SrcSizeInBits / 2;
   InVT = EVT::getVectorVT(Ctx, InVT, SubSizeInBits / InVT.getSizeInBits());
   OutVT = EVT::getVectorVT(Ctx, OutVT, SubSizeInBits / OutVT.getSizeInBits());
 
   // Split lower/upper subvectors.
   SDValue Lo = extractSubVector(In, 0, DAG, DL, SubSizeInBits);
   SDValue Hi = extractSubVector(In, NumElems / 2, DAG, DL, SubSizeInBits);
 
-  // 256bit -> 128bit truncate - PACK lower/upper 128-bit subvectors.
+  // 256bit -> 128bit truncate - Narrow lower/upper 128-bit subvectors.
   if (SrcVT.is256BitVector() && DstVT.is128BitVector()) {
     Lo = DAG.getBitcast(InVT, Lo);
     Hi = DAG.getBitcast(InVT, Hi);
     SDValue Res = DAG.getNode(Opcode, DL, OutVT, Lo, Hi);
     return DAG.getBitcast(DstVT, Res);
   }
 
-  // Recursively pack lower/upper subvectors, concat result and pack again.
+  // Recursively narrow lower/upper subvectors, concat result and narrow again.
   EVT PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems / 2);
   Lo = truncateVectorWithNARROW(Opcode, PackedVT, Lo, DL, DAG);
   Hi = truncateVectorWithNARROW(Opcode, PackedVT, Hi, DL, DAG);
 
   PackedVT = EVT::getVectorVT(Ctx, PackedSVT, NumElems);
   SDValue Res = DAG.getNode(ISD::CONCAT_VECTORS, DL, PackedVT, Lo, Hi);
   return truncateVectorWithNARROW(Opcode, DstVT, Res, DL, DAG);
 }