[SelectionDAG] Add a check to getVectorShuffle to ensure that the only negative index we allow is -1.

llvm-svn: 316183

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -1486,7 +1486,8 @@ SDValue SelectionDAG::getVectorShuffle(EVT VT, const SDLoc &dl, SDValue N1,
   // Validate that all indices in Mask are within the range of the elements
   // input to the shuffle.
   int NElts = Mask.size();
-  assert(llvm::all_of(Mask, [&](int M) { return M < (NElts * 2); }) &&
+  assert(llvm::all_of(Mask,
+                      [&](int M) { return M < (NElts * 2) && M >= -1; }) &&
          "Index out of range");
 
   // Copy the mask so we can do any needed cleanup.