[X86] Size a SmallVector to the worst case mask size for a 512-bit shuffle. NFCI

llvm-svn: 287908
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 1273482..b6c32c02 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -1547,7 +1547,7 @@
 
     const MachineOperand &MaskOp = MI->getOperand(MaskIdx);
     if (auto *C = getConstantFromPool(*MI, MaskOp)) {
-      SmallVector<int, 16> Mask;
+      SmallVector<int, 64> Mask;
       DecodePSHUFBMask(C, Mask);
       if (!Mask.empty())
         OutStreamer->AddComment(getShuffleComment(MI, SrcIdx, SrcIdx, Mask));