158 lines
4.1 KiB
C
158 lines
4.1 KiB
C
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/**
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* GCC compatible wrappers around clang attributes.
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*
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* @author Dominik Gabi
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*/
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#pragma once
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#include <folly/Portability.h>
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#ifndef __has_attribute
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#define FOLLY_HAS_ATTRIBUTE(x) 0
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#else
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#define FOLLY_HAS_ATTRIBUTE(x) __has_attribute(x)
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#endif
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#ifndef __has_cpp_attribute
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#define FOLLY_HAS_CPP_ATTRIBUTE(x) 0
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#else
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#define FOLLY_HAS_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
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#endif
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#ifndef __has_extension
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#define FOLLY_HAS_EXTENSION(x) 0
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#else
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#define FOLLY_HAS_EXTENSION(x) __has_extension(x)
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#endif
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/**
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* Fallthrough to indicate that `break` was left out on purpose in a switch
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* statement, e.g.
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*
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* switch (n) {
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* case 22:
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* case 33: // no warning: no statements between case labels
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* f();
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* case 44: // warning: unannotated fall-through
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* g();
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* FOLLY_FALLTHROUGH; // no warning: annotated fall-through
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* }
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*/
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#if FOLLY_HAS_CPP_ATTRIBUTE(fallthrough)
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#define FOLLY_FALLTHROUGH [[fallthrough]]
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#elif FOLLY_HAS_CPP_ATTRIBUTE(clang::fallthrough)
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#define FOLLY_FALLTHROUGH [[clang::fallthrough]]
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#elif FOLLY_HAS_CPP_ATTRIBUTE(gnu::fallthrough)
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#define FOLLY_FALLTHROUGH [[gnu::fallthrough]]
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#else
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#define FOLLY_FALLTHROUGH
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#endif
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/**
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* Maybe_unused indicates that a function, variable or parameter might or
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* might not be used, e.g.
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*
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* int foo(FOLLY_MAYBE_UNUSED int x) {
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* #ifdef USE_X
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* return x;
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* #else
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* return 0;
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* #endif
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* }
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*/
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#if FOLLY_HAS_CPP_ATTRIBUTE(maybe_unused)
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#define FOLLY_MAYBE_UNUSED [[maybe_unused]]
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#elif FOLLY_HAS_ATTRIBUTE(__unused__) || __GNUC__
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#define FOLLY_MAYBE_UNUSED __attribute__((__unused__))
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#else
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#define FOLLY_MAYBE_UNUSED
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#endif
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/**
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* Nullable indicates that a return value or a parameter may be a `nullptr`,
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* e.g.
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*
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* int* FOLLY_NULLABLE foo(int* a, int* FOLLY_NULLABLE b) {
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* if (*a > 0) { // safe dereference
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* return nullptr;
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* }
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* if (*b < 0) { // unsafe dereference
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* return *a;
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* }
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* if (b != nullptr && *b == 1) { // safe checked dereference
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* return new int(1);
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* }
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* return nullptr;
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* }
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*
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* Ignores Clang's -Wnullability-extension since it correctly handles the case
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* where the extension is not present.
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*/
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#if FOLLY_HAS_EXTENSION(nullability)
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#define FOLLY_NULLABLE \
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FOLLY_PUSH_WARNING \
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FOLLY_CLANG_DISABLE_WARNING("-Wnullability-extension") \
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_Nullable FOLLY_POP_WARNING
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#define FOLLY_NONNULL \
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FOLLY_PUSH_WARNING \
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FOLLY_CLANG_DISABLE_WARNING("-Wnullability-extension") \
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_Nonnull FOLLY_POP_WARNING
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#else
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#define FOLLY_NULLABLE
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#define FOLLY_NONNULL
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#endif
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/**
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* "Cold" indicates to the compiler that a function is only expected to be
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* called from unlikely code paths. It can affect decisions made by the
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* optimizer both when processing the function body and when analyzing
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* call-sites.
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*/
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#if __GNUC__
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#define FOLLY_COLD __attribute__((__cold__))
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#else
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#define FOLLY_COLD
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#endif
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/**
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* no_unique_address indicates that a member variable can be optimized to
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* occupy no space, rather than the minimum 1-byte used by default.
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*
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* class Empty {};
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*
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* class NonEmpty1 {
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* FOLLY_NO_UNIQUE_ADDRESS Empty e;
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* int f;
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* };
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*
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* class NonEmpty2 {
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* Empty e;
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* int f;
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* };
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*
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* sizeof(NonEmpty1); // may be == sizeof(int)
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* sizeof(NonEmpty2); // must be > sizeof(int)
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*/
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#if FOLLY_HAS_CPP_ATTRIBUTE(no_unique_address)
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#define FOLLY_ATTR_NO_UNIQUE_ADDRESS [[no_unique_address]]
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#else
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#define FOLLY_ATTR_NO_UNIQUE_ADDRESS
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#endif
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