Implement a small subset of the C++ `type_traits` header inside sanitizer_common so we can avoid depending on system C++ headers.

[delcypher]

Summary

In particular we implement the is_same<T,U> templated type. This is
useful for doing compile-time comparison of types in static_asserts.
The plan is to use this in another patch (
https://reviews.llvm.org/D54904 ).

[delcypher]

Ping.

[vitalybuka]

I don't see it in D54904

[cryptoad]

In D54951#1325058, @vitalybuka wrote:

I don't see it in D54904

It was removed after https://reviews.llvm.org/D54904?id=175500.
Is this patch still necessary?

[delcypher]

In D54951#1325415, @cryptoad wrote:

In D54951#1325058, @vitalybuka wrote:

I don't see it in D54904

It was removed after https://reviews.llvm.org/D54904?id=175500.
Is this patch still necessary?

@cryptoad
I'd like to still land it if possible. I intend to use this in future patches. I removed it from https://reviews.llvm.org/D54904 to simply have less code to review. My intention is to land this and then add the static_assert(...) that I wanted to write original in a future patch.

[vitalybuka]

@cryptoad
I'd like to still land it if possible. I intend to use this in future patches. I removed it from https://reviews.llvm.org/D54904 to simply have less code to review. My intention is to land this and then add the static_assert(...) that I wanted to write original in a future patch.

Then we can review it with dependent patch?
There is probability that dependent patch will be changed during review or other reasons and we stuck with small but unused piece of code.

[delcypher]

In D54951#1325854, @vitalybuka wrote:

@cryptoad
I'd like to still land it if possible. I intend to use this in future patches. I removed it from https://reviews.llvm.org/D54904 to simply have less code to review. My intention is to land this and then add the static_assert(...) that I wanted to write original in a future patch.

Then we can review it with dependent patch?
There is probability that dependent patch will be changed during review or other reasons and we stuck with small but unused piece of code.

Okay. I'll merge this patch back into https://reviews.llvm.org/D54904?id=175500

[vitalybuka]

the last snapshot of D54904 has no references to is_same
However if D54904 (or other in the stack) has static_assert, then this patch LGTM

[delcypher]

Oops. Sorry I misinterpreted what you meant. I'm reclaiming this revision.

lib/sanitizer_common/sanitizer_type_traits.h

+//===-- sanitizer_type_traits.h ---------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Implements a subset of C++ type traits. This is so we can avoid depending
+// on system C++ headers.
+//
+//===----------------------------------------------------------------------===//
+#ifndef SANITIZER_TYPE_TRAITS_H
+#define SANITIZER_TYPE_TRAITS_H
+
+namespace __sanitizer {
+
+struct true_type {
+  static const bool value = true;
+};
+
+struct false_type {
+  static const bool value = false;
+};
+
+// is_same<T, U>
+//
+// Type trait to compare if types are the same.
+// E.g.
+//
+// ```
+// is_same<int,int>::value - True
+// is_same<int,char>::value - False
+// ```
+template <typename T, typename U>
+struct is_same : public false_type {};
+
+template <typename T>
+struct is_same<T, T> : public true_type {};
+
+};  // namespace __sanitizer
+
+#endif

lib/sanitizer_common/tests/CMakeLists.txt

set(SANITIZER_UNITTESTS
   sanitizer_stackdepot_test.cc
   sanitizer_stacktrace_printer_test.cc
   sanitizer_stacktrace_test.cc
   sanitizer_stoptheworld_test.cc
   sanitizer_suppressions_test.cc
   sanitizer_symbolizer_test.cc
   sanitizer_test_main.cc
   sanitizer_thread_registry_test.cc
+  sanitizer_type_traits_test.cc
   sanitizer_vector_test.cc)
 
 set(SANITIZER_TEST_HEADERS
   sanitizer_pthread_wrappers.h
   sanitizer_test_config.h
   sanitizer_test_utils.h)
 foreach(header ${SANITIZER_IMPL_HEADERS})
   list(APPEND SANITIZER_TEST_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/../${header})

lib/sanitizer_common/tests/sanitizer_type_traits_test.cc

+//===-- sanitizer_type_traits_test.cc -------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of ThreadSanitizer/AddressSanitizer runtime.
+//
+//===----------------------------------------------------------------------===//
+#include "sanitizer_common/sanitizer_type_traits.h"
+#include "gtest/gtest.h"
+#include "sanitizer_common/sanitizer_internal_defs.h"
+
+using namespace __sanitizer;
+
+TEST(SanitizerCommon, IsSame) {
+  ASSERT_TRUE((is_same<unsigned, unsigned>::value));
+  ASSERT_TRUE((is_same<uptr, uptr>::value));
+  ASSERT_TRUE((is_same<sptr, sptr>::value));
+  ASSERT_TRUE((is_same<const uptr, const uptr>::value));
+
+  ASSERT_FALSE((is_same<unsigned, signed>::value));
+  ASSERT_FALSE((is_same<uptr, sptr>::value));
+  ASSERT_FALSE((is_same<uptr, const uptr>::value));
+}