[X86][AMX] Add check for potentially dereferencing null return value

[yubing]

in fact if replaceWithTileLoad's IsPHI=true, U must be a PHINode's uses, V must be PHINode. i checked replacePhiDefWithLoad, replaceWithTileLoad's IsPHI=true, U is passed by a PHI's uses.

[xiangzhangllvm]

llvm/lib/Target/X86/X86LowerAMXType.cpp

491

Make sense for type check, but any bug meet by previous code?

[yubing]

llvm/lib/Target/X86/X86LowerAMXType.cpp

491

i don't know if there is a bug, i just observe a potential dereferencing null return value

[yubing]

rebase

llvm/lib/Target/X86/X86LowerAMXType.cpp

 
 static void replaceWithTileLoad(Use &U, Value *Ptr, bool IsPHI = false) {
   Value *V = U.get();
   assert(V->getType()->isX86_AMXTy() && "Not define tile!");
 
   // Get tile shape.
   IntrinsicInst *II = nullptr;
   if (IsPHI) {
-    Value *PhiOp = dyn_cast<PHINode>(V)->getIncomingValue(0);
+    Value *PhiOp = cast<PHINode>(V)->getIncomingValue(0);
     II = cast<IntrinsicInst>(PhiOp);
   } else {
     II = cast<IntrinsicInst>(V);
   }
   Value *Row = II->getOperand(0);
   Value *Col = II->getOperand(1);
 
   Instruction *UserI = dyn_cast<Instruction>(U.getUser());