[instCombine][bugfix] Fix crash caused by using of cast in instCombineSVECmpNE.

Func instCombineSVECmpNE is used to identify specific pattern of instruction
'svecmene',
and then predict its result, use the result to replace instruction 'svecmene'.
The specific pattern can be descriped below:
1.The svecmpne must compare all elements of vec.
2.The svecmpne inst compare its ves with zero.
3.The vec in svecmpne inst is generated by inst dupqlane, and the copy
value of this dupqlane must be zero.
In NO.3 above, func instCombineSVECmpNE uses 'cast' to transform op1 of
dupqlane without checking if the cast is success, then generate a crash
in some situation.

Author: cceerczw

llvm/lib/Target/AArch64/AArch64TargetTransformInfo.cpp

@@ -1174,7 +1174,8 @@ static std::optional<Instruction *> instCombineSVECmpNE(InstCombiner &IC,
     return std::nullopt;
 
   // Where the dupq is a lane 0 replicate of a vector insert
-  if (!cast<ConstantInt>(DupQLane->getArgOperand(1))->isZero())
+  auto *DupQLaneIdx = dyn_cast<ConstantInt>(DupQLane->getArgOperand(1));
+  if (!DupQLaneIdx || !DupQLaneIdx->isZero())
     return std::nullopt;
 
   auto *VecIns = dyn_cast<IntrinsicInst>(DupQLane->getArgOperand(0));