[SYCL] multi_ptr class: fixes for conversion to void multi_ptr

Signed-off-by: Vyacheslav N Klochkov <[email protected]>

Author: v-klochkov

sycl/include/CL/sycl/multi_ptr.hpp

@@ -126,8 +126,11 @@ template <typename ElementType, access::address_space Space> class multi_ptr {
     return reinterpret_cast<ElementType *>(m_Pointer);
   }
 
-  // Explicit conversion to a multi_ptr<void>
-  explicit operator multi_ptr<void, Space>() const;
+  // Implicit conversion to a multi_ptr<void>
+  operator multi_ptr<void, Space>() const {
+    using void_ptr_t = typename detail::PtrValueType<void, Space>::type *;
+    return multi_ptr<void, Space>(reinterpret_cast<void_ptr_t>(m_Pointer));
+  };
 
   // Arithmetic operators
   multi_ptr &operator++() {
@@ -210,6 +213,14 @@ template <access::address_space Space> class multi_ptr<void, Space> {
   multi_ptr(std::nullptr_t) : m_Pointer(nullptr) {}
   ~multi_ptr() = default;
 
+  // TODO: this constructor is a temporary solution for the cases where
+  // the conversion to void multi pointer is used. Without it the compiler
+  // fails due to having 3 different same rank paths available.
+  // The issue is being discussed in Khronos groups now.
+  // See https://gitlab.khronos.org/sycl/Specification/issues/215 for details.
+  template <typename ElementType>
+  multi_ptr(const multi_ptr<ElementType, Space> &ETP) : m_Pointer(ETP.get()) {}
+
   // Assignment operators
   multi_ptr &operator=(const multi_ptr &) = default;
   multi_ptr &operator=(multi_ptr &&) = default;