[libc] Add a library of standalone C++ utilities.

Some of the existing utils in utils/UnitTest/Test.h have been moved to
this new library.

Reviewers: abrachet, gchatelet

Tags: #libc-project

Differential Revision: https://reviews.llvm.org/D73530

libc/CMakeLists.txt

@@ -1,5 +1,8 @@
 cmake_minimum_required(VERSION 3.4.3)
 
+# Use old version of target_sources command which converts the source
+# file paths to full paths.
+cmake_policy(SET CMP0076 OLD)
 list(APPEND CMAKE_MODULE_PATH  "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
 
 # The top-level source directory of libc.

libc/cmake/modules/LLVMLibCRules.cmake

@@ -375,3 +375,47 @@ function(add_libc_testsuite suite_name)
   add_custom_target(${suite_name})
   add_dependencies(check-libc ${suite_name})
 endfunction(add_libc_testsuite)
+
+# Rule to add header only libraries.
+# Usage
+#    add_header_library(
+#      <target name>
+#      HDRS  <list of .h files part of the library>
+#      DEPENDS <list of dependencies>
+#    )
+function(add_header_library target_name)
+  cmake_parse_arguments(
+    "ADD_HEADER"
+    "" # No optional arguments
+    "" # No Single value arguments
+    "HDRS;DEPENDS" # Multi-value arguments
+    ${ARGN}
+  )
+
+  if(NOT ADD_HEADER_HDRS)
+    message(FATAL_ERROR "'add_header_library' target requires a HDRS list of .h files.")
+  endif()
+
+  set(FULL_HDR_PATHS "")
+  # TODO: Remove this foreach block when we can switch to the new
+  # version of the CMake policy CMP0076.
+  foreach(hdr IN LISTS ADD_HEADER_HDRS)
+    list(APPEND FULL_HDR_PATHS ${CMAKE_CURRENT_SOURCE_DIR}/${hdr})
+  endforeach()
+
+  set(interface_target_name "${target_name}_header_library__")
+
+  add_library(${interface_target_name} INTERFACE)
+  target_sources(${interface_target_name} INTERFACE ${FULL_HDR_PATHS})
+  if(ADD_HEADER_DEPENDS)
+    add_dependencies(${interface_target_name} ${ADD_HEADER_DEPENDS})
+  endif()
+
+  add_custom_target(${target_name})
+  add_dependencies(${target_name} ${interface_target_name})
+  set_target_properties(
+    ${target_name}
+    PROPERTIES
+      "TARGET_TYPE" "HDR_LIBRARY"
+  )
+endfunction(add_header_library)

libc/utils/CMakeLists.txt

@@ -1,3 +1,4 @@
+add_subdirectory(CPP)
 add_subdirectory(HdrGen)
 add_subdirectory(UnitTest)
 add_subdirectory(benchmarks)

libc/utils/CPP/Array.h

@@ -0,0 +1,47 @@
+//===--------- A self contained equivalent of std::array --------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include <stddef.h> // For size_t.
+
+namespace __llvm_libc {
+namespace cpp {
+
+template <class T, size_t N> struct Array {
+  static_assert(N != 0, "Cannot create a __llvm_libc::cpp::Array of size 0.");
+
+  T Data[N];
+
+  using iterator = T *;
+  using const_iterator = const T *;
+
+  constexpr T *data() { return Data; }
+  constexpr const T *data() const { return Data; }
+
+  constexpr T &front() { return Data[0]; }
+  constexpr T &front() const { return Data[0]; }
+
+  constexpr T &back() { return Data[N - 1]; }
+  constexpr T &back() const { return Data[N - 1]; }
+
+  constexpr T &operator[](size_t Index) { return Data[Index]; }
+
+  constexpr const T &operator[](size_t Index) const { return Data[Index]; }
+
+  constexpr size_t size() const { return N; }
+
+  constexpr bool empty() const { return N == 0; }
+
+  constexpr iterator begin() { return Data; }
+  constexpr const_iterator begin() const { return Data; }
+
+  constexpr iterator end() { return Data + N; }
+  const_iterator end() const { return Data + N; }
+};
+
+} // namespace cpp
+} // namespace __llvm_libc

libc/utils/CPP/ArrayRef.h

@@ -0,0 +1,90 @@
+//===----------------- Self contained ArrayRef type -------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "Array.h"
+
+#include <stddef.h> // For size_t.
+
+namespace __llvm_libc {
+namespace cpp {
+
+// The implementations of ArrayRef and MutualArrayRef in this file are based
+// on the implementations of the types with the same names in
+// llvm/ADT/ArrayRef.h. The implementations in this file are of a limited
+// functionality, but can be extended in an as needed basis.
+
+template <typename T> class ArrayRef {
+public:
+  using iterator = const T *;
+
+private:
+  const T *Data = nullptr;
+  size_t Length = 0;
+
+public:
+  ArrayRef() = default;
+
+  // From Array.
+  template <size_t N>
+  ArrayRef(const Array<T, N> &Arr) : Data(Arr.Data), Length(N) {}
+
+  // Construct an ArrayRef from a single element.
+  explicit ArrayRef(const T &OneElt) : Data(&OneElt), Length(1) {}
+
+  // Construct an ArrayRef from a pointer and length.
+  ArrayRef(const T *data, size_t length) : Data(data), Length(length) {}
+
+  // Construct an ArrayRef from a range.
+  ArrayRef(const T *begin, const T *end) : Data(begin), Length(end - begin) {}
+
+  // Construct an ArrayRef from a C array.
+  template <size_t N>
+  constexpr ArrayRef(const T (&Arr)[N]) : Data(Arr), Length(N) {}
+
+  iterator begin() const { return Data; }
+  iterator end() const { return Data + Length; }
+
+  bool empty() const { return Length == 0; }
+
+  const T *data() const { return Data; }
+
+  size_t size() const { return Length; }
+
+  const T &operator[](size_t Index) const { return Data[Index]; }
+};
+
+template <typename T> class MutableArrayRef : public ArrayRef<T> {
+public:
+  using iterator = T *;
+
+  // From Array.
+  template <size_t N> MutableArrayRef(Array<T, N> &Arr) : ArrayRef<T>(Arr) {}
+
+  // Construct from a single element.
+  explicit MutableArrayRef(T &OneElt) : ArrayRef<T>(OneElt) {}
+
+  // Construct from a pointer and length.
+  MutableArrayRef(T *data, size_t length) : ArrayRef<T>(data, length) {}
+
+  // Construct from a range.
+  MutableArrayRef(T *begin, T *end) : ArrayRef<T>(begin, end) {}
+
+  // Construct from a C array.
+  template <size_t N>
+  constexpr MutableArrayRef(T (&Arr)[N]) : ArrayRef<T>(Arr) {}
+
+  T *data() const { return const_cast<T *>(ArrayRef<T>::data()); }
+
+  iterator begin() const { return data(); }
+  iterator end() const { return data() + size(); }
+
+  T &operator[](size_t Index) const { return data()[Index]; }
+};
+
+} // namespace cpp
+} // namespace __llvm_libc

libc/utils/CPP/CMakeLists.txt

@@ -0,0 +1,7 @@
+add_header_library(
+  standalone_cpp
+  HDRS
+    Array.h
+    ArrayRef.h
+    TypeTraits.h
+)

libc/utils/CPP/README.md

@@ -0,0 +1,12 @@
+This directory contains re-implementations of some C++ standard library as well
+as some LLVM utilities. These are to be used with internal LLVM libc code and
+tests. More utilities will be added on an as needed basis. There are certain
+rules to be followed for future changes and additions:
+
+1. Only two kind of headers can be included: Other headers from this directory,
+and free standing C headers.
+2. Free standing C headers are to be included as C headers and not as C++
+headers. That is, use `#include <stddef.h>` and not `#include <cstddef>`.
+3. The utilities should be defined in the namespace `__llvm_libc::cpp`. The
+higher level namespace should have a `__` prefix to avoid symbol name pollution
+when the utilities are used in implementation of public functions.

libc/utils/CPP/StringRef.h

@@ -0,0 +1,19 @@
+//===----------------- A standalone StringRef type  -------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "ArrayRef.h"
+
+namespace __llvm_libc {
+namespace cpp {
+
+class StringRef : public ArrayRef<char> {
+  // More methods like those in llvm::StringRef can be added as needed.
+};
+
+} // namespace cpp
+} // namespace __llvm_libc

libc/utils/CPP/TypeTraits.h

@@ -0,0 +1,50 @@
+//===----------------- Self contained C++ type traits -----------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+namespace __llvm_libc {
+namespace cpp {
+
+template <bool B, typename T> struct EnableIf;
+template <typename T> struct EnableIf<true, T> { typedef T Type; };
+
+template <bool B, typename T>
+using EnableIfType = typename EnableIf<B, T>::Type;
+
+struct TrueValue {
+  static constexpr bool Value = true;
+};
+
+struct FalseValue {
+  static constexpr bool Value = false;
+};
+
+template <typename Type> struct IsIntegral : public FalseValue {};
+template <> struct IsIntegral<char> : public TrueValue {};
+template <> struct IsIntegral<signed char> : public TrueValue {};
+template <> struct IsIntegral<unsigned char> : public TrueValue {};
+template <> struct IsIntegral<short> : public TrueValue {};
+template <> struct IsIntegral<unsigned short> : public TrueValue {};
+template <> struct IsIntegral<int> : public TrueValue {};
+template <> struct IsIntegral<unsigned int> : public TrueValue {};
+template <> struct IsIntegral<long> : public TrueValue {};
+template <> struct IsIntegral<unsigned long> : public TrueValue {};
+template <> struct IsIntegral<long long> : public TrueValue {};
+template <> struct IsIntegral<unsigned long long> : public TrueValue {};
+template <> struct IsIntegral<bool> : public TrueValue {};
+
+template <typename Type> struct IsIntegralNotBool : public IsIntegral<Type> {};
+template <> struct IsIntegralNotBool<bool> : public FalseValue {};
+
+template <typename T> struct IsPointerType : public FalseValue {};
+template <typename T> struct IsPointerType<T *> : public TrueValue {};
+
+template <typename T1, typename T2> struct IsSame : public FalseValue {};
+template <typename T> struct IsSame<T, T> : public TrueValue {};
+
+} // namespace cpp
+} // namespace __llvm_libc

libc/utils/UnitTest/CMakeLists.txt

@@ -4,3 +4,5 @@ add_llvm_library(
   Test.h
   LINK_COMPONENTS Support
 )
+target_include_directories(LibcUnitTest PUBLIC ${LIBC_SOURCE_DIR})
+add_dependencies(LibcUnitTest standalone_cpp)

libc/utils/UnitTest/Test.cpp

@@ -11,7 +11,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/raw_ostream.h"
 
-namespace llvm_libc {
+namespace __llvm_libc {
 namespace testing {
 
 // This need not be a class as all it has is a single read-write state variable.
@@ -224,6 +224,6 @@ bool Test::testStrNe(RunContext &Ctx, const char *LHS, const char *RHS,
 }
 
 } // namespace testing
-} // namespace llvm_libc
+} // namespace __llvm_libc
 
-int main() { return llvm_libc::testing::Test::runTests(); }
+int main() { return __llvm_libc::testing::Test::runTests(); }