Remove unused variable.

[dnovillo]

Summary

This variable is only used inside an assert. This breaks builds with
asserts disabled.

OK for trunk?

[RKSimon]

Thanks Diego!

lib/Target/X86/Utils/X86ShuffleDecode.cpp

for (int i = 0; i < NumElements; ++i) {
       // Only the least significant 2 bits of the integer are used.
       int Index = Base + (Element & 0x3);
       ShuffleMask.push_back(Index);
     }
   }
 }
 
 void DecodeZeroExtendMask(MVT SrcVT, MVT DstVT, SmallVectorImpl<int> &Mask) {
-  unsigned NumSrcElts = SrcVT.getVectorNumElements();
   unsigned NumDstElts = DstVT.getVectorNumElements();
   unsigned SrcScalarBits = SrcVT.getScalarSizeInBits();
   unsigned DstScalarBits = DstVT.getScalarSizeInBits();
   unsigned Scale = DstScalarBits / SrcScalarBits;
   assert(SrcScalarBits < DstScalarBits &&
          "Expected zero extension mask to increase scalar size");
-  assert(NumSrcElts >= NumDstElts && "Too many zero extension lanes");
+  assert(SrcVT.getVectorNumElements() >= NumDstElts &&
+         "Too many zero extension lanes");
 
   for (unsigned i = 0; i != NumDstElts; i++) {
     Mask.push_back(i);
     for (unsigned j = 1; j != Scale; j++)
       Mask.push_back(SM_SentinelZero);
   }
 }