[SYCL][NFCI] Unify queue submit paths (#15776)

The submit method on queue has caused multiple divergences throughout
its lifetime, when additional information was required for new
functionality. However, that design means an exponential growth in
functions every time a new optional argument is needed. To battle this,
this patch adds a new pimpl class with the optional submission info,
which will only be initialized if needed. This boils the submit function
paths down to one with event and one without.

---------

Signed-off-by: Larsen, Steffen <[email protected]>

Author: steffenlarsen

sycl/include/sycl/detail/optional.hpp

@@ -0,0 +1,147 @@
+//==-------- optional.hpp - limited variant of std::optional -------- C++ --==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// ===--------------------------------------------------------------------=== //
+
+#pragma once
+
+#include <optional>
+#include <type_traits>
+
+namespace sycl {
+inline namespace _V1 {
+namespace detail {
+
+// ABI-stable implementation of optional to avoid reliance on potentially
+// differing implementations of std::optional when crossing the library
+// boundary.
+template <typename T> class optional {
+public:
+  constexpr optional() noexcept {}
+  constexpr optional(std::nullopt_t) noexcept : optional() {}
+
+  template <typename U>
+  constexpr optional(const optional<U> &Other)
+      : ContainsValue{Other.ContainsValue} {
+    new (Storage) T(Other.Value);
+  }
+  template <typename U>
+  constexpr optional(optional<U> &&Other)
+      : ContainsValue{std::move(Other.ContainsValue)} {
+    new (Storage) T(std::move(Other.Value));
+  }
+
+  constexpr optional(T &&Value) : ContainsValue{true} {
+    new (Storage) T(std::move(Value));
+  }
+
+  constexpr optional(const T &Value) : ContainsValue{true} {
+    new (Storage) T(Value);
+  }
+
+  template <typename U>
+  constexpr optional(const std::optional<U> &Other) : ContainsValue{Other} {
+    if (Other)
+      new (Storage) T(*Other);
+  }
+
+  ~optional() {
+    if (has_value())
+      reinterpret_cast<T *>(Storage)->~T();
+  }
+
+  optional &operator=(std::nullopt_t) noexcept {
+    if (has_value())
+      reinterpret_cast<T *>(Storage)->~T();
+    ContainsValue = false;
+    return *this;
+  }
+
+  template <typename U> optional &operator=(const optional<U> &Other) {
+    if (has_value())
+      reinterpret_cast<T *>(Storage)->~T();
+    ContainsValue = Other;
+    new (Storage) T(Other.Value);
+    return *this;
+  }
+  template <typename U> optional &operator=(optional<U> &&Other) noexcept {
+    if (has_value())
+      reinterpret_cast<T *>(Storage)->~T();
+    ContainsValue = Other;
+    new (Storage) T(std::move(Other.Value));
+    return *this;
+  }
+
+  optional &operator=(T &&Value) {
+    if (has_value())
+      reinterpret_cast<T *>(Storage)->~T();
+    ContainsValue = true;
+    new (Storage) T(std::move(Value));
+    return *this;
+  }
+
+  optional &operator=(const T &Value) {
+    if (has_value())
+      reinterpret_cast<T *>(Storage)->~T();
+    ContainsValue = true;
+    new (Storage) T(Value);
+    return *this;
+  }
+
+  template <typename U> optional &operator=(const std::optional<U> &Other) {
+    if (has_value())
+      reinterpret_cast<T *>(Storage)->~T();
+    ContainsValue = Other;
+    if (Other)
+      new (Storage) T(*Other);
+    return *this;
+  }
+
+  constexpr bool has_value() const noexcept { return ContainsValue; }
+  constexpr explicit operator bool() const noexcept { return has_value(); }
+
+  constexpr T &value() & {
+    if (!has_value())
+      throw std::bad_optional_access{};
+    return *reinterpret_cast<T *>(Storage);
+  }
+  constexpr const T &value() const & {
+    if (!has_value())
+      throw std::bad_optional_access{};
+    return *reinterpret_cast<const T *>(Storage);
+  }
+  constexpr T &&value() && {
+    if (!has_value())
+      throw std::bad_optional_access{};
+    return std::move(*reinterpret_cast<T *>(Storage));
+  }
+  constexpr const T &&value() const && {
+    if (!has_value())
+      throw std::bad_optional_access{};
+    return std::move(*reinterpret_cast<const T *>(Storage));
+  }
+
+  template <class U> constexpr T value_or(U &&DefaultVal) {
+    return has_value() ? value() : static_cast<T>(std::forward<U>(DefaultVal));
+  }
+  template <class U> constexpr T value_or(U &&DefaultVal) const {
+    return has_value() ? std::move(value())
+                       : static_cast<T>(std::forward<U>(DefaultVal));
+  }
+
+  constexpr T &operator*() & { return value(); }
+  constexpr const T &operator*() const & { return value(); }
+  constexpr T &&operator*() && { return value(); }
+  constexpr const T &&operator*() const && { return value(); }
+
+private:
+  alignas(alignof(T)) char Storage[sizeof(T)] = {0};
+  bool ContainsValue = false;
+};
+
+} // namespace detail
+} // namespace _V1
+} // namespace sycl