[CodeGenPrepare] Use dyn_cast result to check for null pointers

Simplifies logic and helps the static analyzer correctly check for nullptr dereferences

llvm/lib/CodeGen/CodeGenPrepare.cpp

@@ -4168,11 +4168,11 @@ bool TypePromotionHelper::canGetThrough(const Instruction *Inst,
 
   // We can get through binary operator, if it is legal. In other words, the
   // binary operator must have a nuw or nsw flag.
-  const BinaryOperator *BinOp = dyn_cast<BinaryOperator>(Inst);
-  if (isa_and_nonnull<OverflowingBinaryOperator>(BinOp) &&
-      ((!IsSExt && BinOp->hasNoUnsignedWrap()) ||
-       (IsSExt && BinOp->hasNoSignedWrap())))
-    return true;
+  if (const auto *BinOp = dyn_cast<BinaryOperator>(Inst))
+    if (isa<OverflowingBinaryOperator>(BinOp) &&
+        ((!IsSExt && BinOp->hasNoUnsignedWrap()) ||
+         (IsSExt && BinOp->hasNoSignedWrap())))
+      return true;
 
   // ext(and(opnd, cst)) --> and(ext(opnd), ext(cst))
   if ((Inst->getOpcode() == Instruction::And ||
@@ -4181,10 +4181,10 @@ bool TypePromotionHelper::canGetThrough(const Instruction *Inst,
 
   // ext(xor(opnd, cst)) --> xor(ext(opnd), ext(cst))
   if (Inst->getOpcode() == Instruction::Xor) {
-    const ConstantInt *Cst = dyn_cast<ConstantInt>(Inst->getOperand(1));
     // Make sure it is not a NOT.
-    if (Cst && !Cst->getValue().isAllOnes())
-      return true;
+    if (const auto *Cst = dyn_cast<ConstantInt>(Inst->getOperand(1)))
+      if (!Cst->getValue().isAllOnes())
+        return true;
   }
 
   // zext(shrl(opnd, cst)) --> shrl(zext(opnd), zext(cst))