Fix a possible cause of UB and add a check for join output sizes that…

… exceed cudf limits.

cpp/include/cudf/ast/detail/expression_evaluator.cuh

@@ -115,14 +115,15 @@ struct value_expression_result
   /**
    * @brief Returns the underlying data.
    *
-   * @throws thrust::bad_optional_access if the underlying data is not valid.
+   * If the underlying data is not valid, behavior is undefined. Callers should
+   * use is_valid to check for validity before accessing the value.
    */
   __device__ T value() const
   {
     // Using two separate constexprs silences compiler warnings, whereas an
     // if/else does not. An unconditional return is not ignored by the compiler
     // when has_nulls is true and therefore raises a compiler error.
-    if constexpr (has_nulls) { return _obj.value(); }
+    if constexpr (has_nulls) { return *_obj; }
     if constexpr (!has_nulls) { return _obj; }
   }
 

cpp/src/join/conditional_join.cu

@@ -28,6 +28,8 @@
 
 #include <rmm/cuda_stream_view.hpp>
 
+#include <limits>
+
 namespace cudf {
 namespace detail {
 
@@ -109,6 +111,7 @@ conditional_join(table_view const& left,
   CHECK_CUDA(stream.value());
 
   size_type const join_size = size.value(stream);
+  CUDF_EXPECTS(join_size < std::numeric_limits<size_type>::max(), "The result of this join is too large for a cudf column.");
 
   // If the output size will be zero, we can return immediately.
   if (join_size == 0) {