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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
/**
* Include "mongo/platform/compiler.h" to get compiler-targeted macro definitions and utilities.
*
* The following macros are provided in all compiler environments:
*
*
* MONGO_COMPILER_COLD_FUNCTION
*
* Informs the compiler that the function is cold. This can have the following effects:
* - The function is optimized for size over speed.
* - The function may be placed in a special cold section of the binary, away from other code.
* - Code paths that call this function are considered implicitly unlikely.
*
*
* MONGO_COMPILER_NORETURN
*
* Instructs the compiler that the decorated function will not return through the normal return
* path. All noreturn functions are also implicitly cold since they are either run-once code
* executed at startup or shutdown or code that handles errors by throwing an exception.
*
* Correct: MONGO_COMPILER_NORETURN void myAbortFunction();
*
*
* MONGO_COMPILER_ALIGN_TYPE(ALIGNMENT)
*
* Instructs the compiler to use the given minimum alignment for the decorated type.
*
* Alignments should probably always be powers of two. Also, note that most allocators will not
* be able to guarantee better than 16- or 32-byte alignment.
*
* Correct:
* class MONGO_COMPILER_ALIGN_TYPE(16) MyClass {...};
*
* Incorrect:
* MONGO_COMPILER_ALIGN_TYPE(16) class MyClass {...};
* class MyClass{...} MONGO_COMPILER_ALIGN_TYPE(16);
*
*
* MONGO_COMPILER_ALIGN_VARIABLE(ALIGNMENT)
*
* Instructs the compiler to use the given minimum alignment for the decorated variable.
*
* Note that most allocators will not allow heap allocated alignments that are better than 16- or
* 32-byte aligned. Stack allocators may only guarantee up to the natural word length worth of
* alignment.
*
* Correct:
* class MyClass {
* MONGO_COMPILER_ALIGN_VARIABLE(8) char a;
* };
*
* MONGO_COMPILER_ALIGN_VARIABLE(8) class MyClass {...} singletonInstance;
*
* Incorrect:
* int MONGO_COMPILER_ALIGN_VARIABLE(16) a, b;
*
*
* MONGO_COMPILER_API_EXPORT
*
* Instructs the compiler to label the given type, variable or function as part of the
* exported interface of the library object under construction.
*
* Correct:
* MONGO_COMPILER_API_EXPORT int globalSwitch;
* class MONGO_COMPILER_API_EXPORT ExportedType { ... };
* MONGO_COMPILER_API_EXPORT SomeType exportedFunction(...);
*
* NOTE: Rather than using this macro directly, one typically declares another macro named
* for the library, which is conditionally defined to either MONGO_COMIPLER_API_EXPORT or
* MONGO_COMPILER_API_IMPORT based on whether the compiler is currently building the library
* or building an object that depends on the library, respectively. For example,
* MONGO_FOO_API might be defined to MONGO_COMPILER_API_EXPORT when building the MongoDB
* libfoo shared library, and to MONGO_COMPILER_API_IMPORT when building an application that
* links against that shared library.
*
*
* MONGO_COMPILER_API_IMPORT
*
* Instructs the compiler to label the given type, variable or function as imported
* from another library, and not part of the library object under construction.
*
* Same correct/incorrect usage as for MONGO_COMPILER_API_EXPORT.
*
*
* MONGO_COMPILER_API_CALLING_CONVENTION
*
* Explicitly decorates a function declaration the api calling convention used for
* shared libraries.
*
* Same correct/incorrect usage as for MONGO_COMPILER_API_EXPORT.
*
*
* MONGO_COMPILER_ALWAYS_INLINE
*
* Overrides compiler heuristics to force that a particular function should always
* be inlined.
*
*
* MONGO_COMPILER_UNREACHABLE
*
* Tells the compiler that it can assume that this line will never execute. Unlike with
* MONGO_UNREACHABLE, there is no runtime check and reaching this macro is completely undefined
* behavior. It should only be used where it is provably impossible to reach, even in the face of
* adversarial inputs, but for some reason the compiler cannot figure this out on its own, for
* example after a call to a function that never returns but cannot be labeled with
* MONGO_COMPILER_NORETURN. In almost all cases MONGO_UNREACHABLE is preferred.
*
*
* MONGO_COMPILER_NOINLINE
*
* Tells the compiler that it should not attempt to inline a function. This option is not
* guaranteed to eliminate all optimizations, it only is used to prevent a function from being
* inlined.
*
*
* MONGO_WARN_UNUSED_RESULT_CLASS
*
* Tells the compiler that a class defines a type for which checking results is necessary. Types
* thus defined turn functions returning them into "must check results" style functions. Preview
* of the `[[nodiscard]]` C++17 attribute.
*
*
* MONGO_WARN_UNUSED_RESULT_FUNCTION
*
* Tells the compiler that a function returns a value for which consuming the result is
* necessary. Functions thus defined are "must check results" style functions. Preview of the
* `[[nodiscard]]` C++17 attribute.
*
*
* MONGO_COMPILER_RETURNS_NONNULL
*
* Tells the compiler that the function always returns a non-null value, potentially allowing
* additional optimizations at call sites.
*
*
* MONGO_COMPILER_MALLOC
*
* Tells the compiler that the function is "malloc like", in that the return value points
* to uninitialized memory which does not alias any other valid pointers.
*
*
* MONGO_COMPILER_ALLOC_SIZE(varindex)
*
* Tells the compiler that the parameter indexed by `varindex`
* provides the size of the allocated region that a "malloc like"
* function will return a pointer to, potentially allowing static
* analysis of use of the region when the argument to the
* allocation function is a constant expression.
*
*
* MONGO_GSL_POINTER
*
* Hints to the compiler that this type is a gsl::Pointer type,
* which will produce a compiler warning if this type is assigned
* a temporary (xvalue) gsl::Owner type (such as std::string). This
* matches the annotation libc++ uses for std::string_view.
*/
#if defined(_MSC_VER)
#include "mongo/platform/compiler_msvc.h"
#elif defined(__GNUC__)
#include "mongo/platform/compiler_gcc.h"
#else
#error "Unsupported compiler family"
#endif
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