[ORC] Port CallableTraitsHelper from the new ORC runtime.

The code for this commit was taken with minimal modification to fit LLVM style
from llvm-project/orc-rt/include/orc-rt/CallableTraitsHelper.h and
llvm-project/orc-rt/unittests/CallableTraitsHelperTest.cpp (originally committed
in 40fce32)

CallableTraitsHelper identifies the return type and argument types of a
callable type and passes those to an implementation class template to
operate on. E.g. the CallableArgInfoImpl class exposes these types as
typedefs.

Porting CallableTraitsHelper from the new ORC runtime will allow us to simplify
existing and upcoming "callable-traits" classes in ORC.

Author: lhames

llvm/include/llvm/ExecutionEngine/Orc/CallableTraitsHelper.h

@@ -0,0 +1,74 @@
+//===- CallableTraitsHelper.h - Callable arg/ret type extractor -*- 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
+//
+//===----------------------------------------------------------------------===//
+//
+// CallableTraitsHelper API.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_EXECUTIONENGINE_ORC_CALLABLETRAITSHELPER_H
+#define LLVM_EXECUTIONENGINE_ORC_CALLABLETRAITSHELPER_H
+
+#include <tuple>
+#include <type_traits>
+
+namespace llvm::orc {
+
+/// CallableTraitsHelper takes an implementation class template Impl and some
+/// callable type C and passes the return and argument types of C to the Impl
+/// class template.
+///
+/// This can be used to simplify the implementation of classes that need to
+/// operate on callable types.
+template <template <typename...> typename ImplT, typename C>
+struct CallableTraitsHelper
+    : public CallableTraitsHelper<
+          ImplT,
+          decltype(&std::remove_cv_t<std::remove_reference_t<C>>::operator())> {
+};
+
+template <template <typename...> typename ImplT, typename RetT,
+          typename... ArgTs>
+struct CallableTraitsHelper<ImplT, RetT(ArgTs...)>
+    : public ImplT<RetT, ArgTs...> {};
+
+template <template <typename...> typename ImplT, typename RetT,
+          typename... ArgTs>
+struct CallableTraitsHelper<ImplT, RetT (*)(ArgTs...)>
+    : public CallableTraitsHelper<ImplT, RetT(ArgTs...)> {};
+
+template <template <typename...> typename ImplT, typename RetT,
+          typename... ArgTs>
+struct CallableTraitsHelper<ImplT, RetT (&)(ArgTs...)>
+    : public CallableTraitsHelper<ImplT, RetT(ArgTs...)> {};
+
+template <template <typename...> typename ImplT, typename ClassT, typename RetT,
+          typename... ArgTs>
+struct CallableTraitsHelper<ImplT, RetT (ClassT::*)(ArgTs...)>
+    : public CallableTraitsHelper<ImplT, RetT(ArgTs...)> {};
+
+template <template <typename...> typename ImplT, typename ClassT, typename RetT,
+          typename... ArgTs>
+struct CallableTraitsHelper<ImplT, RetT (ClassT::*)(ArgTs...) const>
+    : public CallableTraitsHelper<ImplT, RetT(ArgTs...)> {};
+
+namespace detail {
+template <typename RetT, typename... ArgTs> struct CallableArgInfoImpl {
+  using ReturnType = RetT;
+  using ArgsTupleType = std::tuple<ArgTs...>;
+};
+} // namespace detail
+
+/// CallableArgInfo provides typedefs for the return type and argument types
+/// (as a tuple) of the given callable type.
+template <typename Callable>
+struct CallableArgInfo
+    : public CallableTraitsHelper<detail::CallableArgInfoImpl, Callable> {};
+
+} // namespace llvm::orc
+
+#endif // LLVM_EXECUTIONENGINE_ORC_CALLABLETRAITSHELPER_H

llvm/unittests/ExecutionEngine/Orc/CMakeLists.txt

@@ -18,6 +18,7 @@ set(LLVM_LINK_COMPONENTS
   )
 
 add_llvm_unittest(OrcJITTests
+  CallableTraitsHelperTest.cpp
   CoreAPIsTest.cpp
   ExecutorAddressTest.cpp
   ExecutionSessionWrapperFunctionCallsTest.cpp

llvm/unittests/ExecutionEngine/Orc/CallableTraitsHelperTest.cpp

@@ -0,0 +1,70 @@
+//===- CallableTraitsHelperTest.cpp ---------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// Tests for llvm::orc::CallableTraitsHelper APIs.
+//
+// NOTE: All tests in this file are testing compile-time functionality, so the
+//       tests at runtime all end up being noops. That's fine -- those are
+//       cheap.
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ExecutionEngine/Orc/CallableTraitsHelper.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace llvm::orc;
+
+static void freeVoidVoid() {}
+
+TEST(CallableTraitsHelperTest, FreeVoidVoid) {
+  (void)freeVoidVoid;
+  typedef CallableArgInfo<decltype(freeVoidVoid)> CAI;
+  static_assert(std::is_void_v<CAI::ReturnType>);
+  static_assert(std::is_same_v<CAI::ArgsTupleType, std::tuple<>>);
+}
+
+static int freeBinaryOp(int, float) { return 0; }
+
+TEST(CallableTraitsHelperTest, FreeBinaryOp) {
+  (void)freeBinaryOp;
+  typedef CallableArgInfo<decltype(freeBinaryOp)> CAI;
+  static_assert(std::is_same_v<CAI::ReturnType, int>);
+  static_assert(std::is_same_v<CAI::ArgsTupleType, std::tuple<int, float>>);
+}
+
+TEST(CallableTraitsHelperTest, VoidVoidObj) {
+  auto VoidVoid = []() {};
+  typedef CallableArgInfo<decltype(VoidVoid)> CAI;
+  static_assert(std::is_void_v<CAI::ReturnType>);
+  static_assert(std::is_same_v<CAI::ArgsTupleType, std::tuple<>>);
+}
+
+TEST(CallableTraitsHelperTest, BinaryOpObj) {
+  auto BinaryOp = [](int X, float Y) -> int { return X + Y; };
+  typedef CallableArgInfo<decltype(BinaryOp)> CAI;
+  static_assert(std::is_same_v<CAI::ReturnType, int>);
+  static_assert(std::is_same_v<CAI::ArgsTupleType, std::tuple<int, float>>);
+}
+
+TEST(CallableTraitsHelperTest, PreservesLValueRef) {
+  auto RefOp = [](int &) {};
+  typedef CallableArgInfo<decltype(RefOp)> CAI;
+  static_assert(std::is_same_v<CAI::ArgsTupleType, std::tuple<int &>>);
+}
+
+TEST(CallableTraitsHelperTest, PreservesLValueRefConstness) {
+  auto RefOp = [](const int &) {};
+  typedef CallableArgInfo<decltype(RefOp)> CAI;
+  static_assert(std::is_same_v<CAI::ArgsTupleType, std::tuple<const int &>>);
+}
+
+TEST(CallableTraitsHelperTest, PreservesRValueRef) {
+  auto RefOp = [](int &&) {};
+  typedef CallableArgInfo<decltype(RefOp)> CAI;
+  static_assert(std::is_same_v<CAI::ArgsTupleType, std::tuple<int &&>>);
+}