1 //===-- include/flang/Common/idioms.h ---------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef FORTRAN_COMMON_IDIOMS_H_
10 #define FORTRAN_COMMON_IDIOMS_H_
11 
12 // Defines anything that might ever be useful in more than one source file
13 // or that is too weird or too specific to the host C++ compiler to be
14 // exposed elsewhere.
15 
16 #ifndef __cplusplus
17 #error this is a C++ program
18 #endif
19 #if __cplusplus < 201703L
20 #error this is a C++17 program
21 #endif
22 #if !__clang__ && defined __GNUC__ && __GNUC__ < 7
23 #error g++ >= 7.2 is required
24 #endif
25 
26 #include "llvm/Support/Compiler.h"
27 #include <functional>
28 #include <list>
29 #include <memory>
30 #include <optional>
31 #include <string>
32 #include <tuple>
33 #include <type_traits>
34 #include <variant>
35 
36 #if __GNUC__ == 7
37 // Avoid a deduction bug in GNU 7.x headers by forcing the answer.
38 namespace std {
39 template <typename A>
40 struct is_trivially_copy_constructible<list<A>> : false_type {};
41 template <typename A>
42 struct is_trivially_copy_constructible<optional<list<A>>> : false_type {};
43 } // namespace std
44 #endif
45 
46 // enable "this is a std::string"s with the 's' suffix
47 using namespace std::literals::string_literals;
48 
49 namespace Fortran::common {
50 
51 // Helper templates for combining a list of lambdas into an anonymous
52 // struct for use with std::visit() on a std::variant<> sum type.
53 // E.g.: std::visit(visitors{
54 //         [&](const firstType &x) { ... },
55 //         [&](const secondType &x) { ... },
56 //         ...
57 //         [&](const auto &catchAll) { ... }}, variantObject);
58 
59 template <typename... LAMBDAS> struct visitors : LAMBDAS... {
60   using LAMBDAS::operator()...;
61 };
62 
63 template <typename... LAMBDAS> visitors(LAMBDAS... x) -> visitors<LAMBDAS...>;
64 
65 // Calls std::fprintf(stderr, ...), then abort().
66 [[noreturn]] void die(const char *, ...);
67 
68 #define DIE(x) Fortran::common::die(x " at " __FILE__ "(%d)", __LINE__)
69 
70 // For switch statement default: labels.
71 #define CRASH_NO_CASE DIE("no case")
72 
73 // clang-format off
74 // For switch statements whose cases have return statements for
75 // all possibilities.  Clang emits warnings if the default: is
76 // present, gcc emits warnings if it is absent.
77 #if __clang__
78 #define SWITCH_COVERS_ALL_CASES
79 #else
80 #define SWITCH_COVERS_ALL_CASES default: CRASH_NO_CASE;
81 #endif
82 // clang-format on
83 
84 // For cheap assertions that should be applied in production.
85 // To disable, compile with '-DCHECK=(void)'
86 #ifndef CHECK
87 #define CHECK(x) ((x) || (DIE("CHECK(" #x ") failed"), false))
88 #endif
89 
90 // User-defined type traits that default to false:
91 // Invoke CLASS_TRAIT(traitName) to define a trait, then put
92 //   using traitName = std::true_type;  (or false_type)
93 // into the appropriate class definitions.  You can then use
94 //   typename std::enable_if_t<traitName<...>, ...>
95 // in template specialization definitions.
96 #define CLASS_TRAIT(T) \
97   namespace class_trait_ns_##T { \
98     template <typename A> std::true_type test(typename A::T *); \
99     template <typename A> std::false_type test(...); \
100     template <typename A> \
101     constexpr bool has_trait{decltype(test<A>(nullptr))::value}; \
102     template <typename A> constexpr bool trait_value() { \
103       if constexpr (has_trait<A>) { \
104         using U = typename A::T; \
105         return U::value; \
106       } else { \
107         return false; \
108       } \
109     } \
110   } \
111   template <typename A> constexpr bool T{class_trait_ns_##T::trait_value<A>()};
112 
113 // Define enum class NAME with the given enumerators, a static
114 // function EnumToString() that maps enumerators to std::string,
115 // and a constant NAME_enumSize that captures the number of items
116 // in the enum class.
117 
118 std::string EnumIndexToString(int index, const char *names);
119 
120 template <typename A> struct ListItemCount {
121   constexpr ListItemCount(std::initializer_list<A> list) : value{list.size()} {}
122   const std::size_t value;
123 };
124 
125 #define ENUM_CLASS(NAME, ...) \
126   enum class NAME { __VA_ARGS__ }; \
127   LLVM_ATTRIBUTE_UNUSED static constexpr std::size_t NAME##_enumSize{[] { \
128     enum { __VA_ARGS__ }; \
129     return Fortran::common::ListItemCount{__VA_ARGS__}.value; \
130   }()}; \
131   LLVM_ATTRIBUTE_UNUSED static inline std::string EnumToString(NAME e) { \
132     return Fortran::common::EnumIndexToString( \
133         static_cast<int>(e), #__VA_ARGS__); \
134   }
135 
136 // Check that a pointer is non-null and dereference it
137 #define DEREF(p) Fortran::common::Deref(p, __FILE__, __LINE__)
138 
139 template <typename T> constexpr T &Deref(T *p, const char *file, int line) {
140   if (!p) {
141     Fortran::common::die("nullptr dereference at %s(%d)", file, line);
142   }
143   return *p;
144 }
145 
146 template <typename T>
147 constexpr T &Deref(const std::unique_ptr<T> &p, const char *file, int line) {
148   if (!p) {
149     Fortran::common::die("nullptr dereference at %s(%d)", file, line);
150   }
151   return *p;
152 }
153 
154 // Given a const reference to a value, return a copy of the value.
155 template <typename A> A Clone(const A &x) { return x; }
156 
157 // C++ does a weird and dangerous thing when deducing template type parameters
158 // from function arguments: lvalue references are allowed to match rvalue
159 // reference arguments.  Template function declarations like
160 //   template<typename A> int foo(A &&);
161 // need to be protected against this C++ language feature when functions
162 // may modify such arguments.  Use these type functions to invoke SFINAE
163 // on a result type via
164 //   template<typename A> common::IfNoLvalue<int, A> foo(A &&);
165 // or, for constructors,
166 //   template<typename A, typename = common::NoLvalue<A>> int foo(A &&);
167 // This works with parameter packs too.
168 template <typename A, typename... B>
169 using IfNoLvalue = std::enable_if_t<(... && !std::is_lvalue_reference_v<B>), A>;
170 template <typename... RVREF> using NoLvalue = IfNoLvalue<void, RVREF...>;
171 } // namespace Fortran::common
172 #endif // FORTRAN_COMMON_IDIOMS_H_
173