gem5  v21.2.1.1
compiler.hh
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1 /*
2  * Copyright (c) 2012,2017-2018 ARM Limited
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14  * Copyright (c) 2006 The Regents of The University of Michigan
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40 
41 #ifndef __BASE_COMPILER_HH__
42 #define __BASE_COMPILER_HH__
43 
44 #include <memory>
45 
46 #include "config/have_deprecated_namespace.hh"
47 
48 // http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
49 
50 
51 /*
52  * Compiler specific features.
53  */
54 
55 #if defined(__GNUC__) // clang or gcc.
56 // Mark a structure as packed, so that no padding is added to its layout. This
57 // padding might be added to, for instance, ensure certain fields have certain
58 // alignment.
59 # define GEM5_PACKED [[gnu::packed]]
60 
61 // Prevent a function from being inlined.
62 # define GEM5_NO_INLINE [[gnu::noinline]]
63 
64 // Set the visibility of a symbol.
65 # define GEM5_PUBLIC [[gnu:visibility("default")]]
66 # define GEM5_LOCAL [[gnu::visibility("hidden")]]
67 # define GEM5_WEAK [[gnu::weak]]
68 
69 // Force an alignment for a variable.
70 # define GEM5_ALIGNED(alignment) [[gnu::aligned(alignment)]]
71 
72 // Marker for what should be an unreachable point in the code.
73 # define GEM5_UNREACHABLE __builtin_unreachable()
74 
75 // To mark a branch condition as likely taken, wrap it's condition with
76 // GEM5_LIKELY. To mark it as likely not taken, wrap it's condition with
77 // GEM5_UNLIKELY. These can be replaced with the standard attributes [[likely]]
78 // and [[unlikely]] in c++20, although the syntax is different enough that
79 // we can't do that with direct substitution.
80 # define GEM5_LIKELY(cond) __builtin_expect(!!(cond), 1)
81 # define GEM5_UNLIKELY(cond) __builtin_expect(!!(cond), 0)
82 
83 // Mark an expression-like macro as deprecated by wrapping it in some code
84 // which declares and uses a deprecated variable with the same name as the
85 // macro. The wrapping macro evaluates to the same thing as the original macro.
86 // The definition must be an c++ expression and not a statement because of how
87 // the original macro is wrapped.
88 # define GEM5_DEPRECATED_MACRO(name, definition, message) \
89  ([](){[[deprecated(message)]] int name{}; return name;}(), (definition))
90 // This version is for macros which are statement-like, which frequently use
91 // "do {} while (0)" to make their syntax look more like normal c++ statements.
92 # define GEM5_DEPRECATED_MACRO_STMT(name, definition, message) \
93  do {{definition;} GEM5_DEPRECATED_MACRO(name, {}, message);} while (0)
94 
95 // To mark a class as deprecated in favor of a new name, add a respective
96 // instance of this macro to the file that used to declare the old name.
97 // This macro should be used *after* the new class has been defined.
98 # define GEM5_DEPRECATED_CLASS(old_class, new_class) \
99  using old_class \
100  [[deprecated("Please use the new class name: '" #new_class "'")]] = \
101  new_class
102 
103 // These macros should be used when namespaces are deprecated in favor of
104 // a new name. They should be used wherever the namespace is declared.
105 // Namespace deprecation is broken for GNU < 10 [1], so there is no
106 // deprecation warning in that case. Clang only supports it from C++17 on.
107 // [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79817
108 # if HAVE_DEPRECATED_NAMESPACE
109 # define GEM5_DEPRECATED_NAMESPACE(old_namespace, new_namespace) \
110  namespace new_namespace {} \
111  namespace [[deprecated("Please use the new namespace: '" \
112  #new_namespace "'")]] old_namespace { \
113  using namespace new_namespace; \
114  }
115 # else
116 # define GEM5_DEPRECATED_NAMESPACE(old_namespace, new_namespace) \
117  namespace new_namespace {} \
118  namespace old_namespace = new_namespace
119 # endif
120 
121 // Evaluate an expanded parameter pack in order. Multiple arguments can be
122 // passed in which be evaluated in order relative to each other as a group.
123 // The argument(s) must include a parameter pack to expand. This works because
124 // the elements of a brace inclosed initializer list are evaluated in order,
125 // as are the arguments to the comma operator, which evaluates to the last
126 // value. This is compiler specific because it uses variadic macros.
127 #define GEM5_FOR_EACH_IN_PACK(...) \
128 do { [[maybe_unused]] int i[] = { 0, ((void)(__VA_ARGS__), 0)... }; } while (0)
129 
130 #else
131 # error "Don't know what to do for your compiler."
132 #endif
133 
134 // When a member variable may be unused, mark it with GEM5_CLASS_VAR_USED. This
135 // needs to be limitted to clang only since clang warns on these unused
136 // variables, and g++ will actually warn if you use this attribute since it
137 // won't do anything there.
138 #if defined(__clang__) // clang only.
139 # define GEM5_CLASS_VAR_USED GEM5_VAR_USED
140 #else
141 # define GEM5_CLASS_VAR_USED
142 #endif
143 
144 // Aliases for macros using the deprecated M5 prefix.
145 #define M5_VAR_USED GEM5_VAR_USED
146 #define M5_NODISCARD GEM5_NO_DISCARD
147 #define M5_FALLTHROUGH GEM5_FALLTHROUGH
148 #define M5_ATTR_PACKED GEM5_PACKED
149 #define M5_NO_INLINE GEM5_NO_INLINE
150 #define M5_PUBLIC GEM5_PUBLIC
151 #define M5_LOCAL GEM5_LOCAL
152 #define M5_WEAK GEM5_WEAK
153 #define M5_ALIGNED(x) GEM5_ALIGNED(x)
154 #define M5_UNREACHABLE GEM5_UNREACHABLE
155 #define M5_LIKELY(x) GEM5_LIKELY(x)
156 #define M5_UNLIKELY(x) GEM5_UNLIKELY(x)
157 #define M5_FOR_EACH_IN_PACK(...) GEM5_FOR_EACH_IN_PACK(__VA_ARGS__)
158 #define M5_CLASS_VAR_USED GEM5_CLASS_VAR_USED
159 
160 // Deprecated attributes which warn.
161 #define GEM5_FALLTHROUGH GEM5_DEPRECATED_MACRO_STMT(GEM5_FALLTHROUGH,,\
162  "Please use the [[fallthrough]] attribute directly."); [[fallthrough]]
163 #define GEM5_DEPRECATED(message) \
164  [[deprecated(message " The GEM5_DEPRECATED macro is also deprecated, "\
165  "please use the [[deprecated()]] attribute directly.")]]
166 #define GEM5_DEPRECATED_ENUM_VAL(message) \
167  [[deprecated(message " The GEM5_DEPRECATED_ENUM_VAL macro is also "\
168  "deprecated, please use the [[deprecated()]] attribute "\
169  "directly.")]]
170 
171 // Deprecated attributes which can't be made to warn without possibly breaking
172 // existing code.
173 #define GEM5_NO_DISCARD [[nodiscard]]
174 #define GEM5_VAR_USED [[maybe_unused]]
175 
176 #endif // __BASE_COMPILER_HH__

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