src/dawn/common/Compiler.h

// Copyright 2017 The Dawn & Tint Authors
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
//    and/or other materials provided with the distribution.
//
// 3. Neither the name of the copyright holder nor the names of its
//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef SRC_DAWN_COMMON_COMPILER_H_
#define SRC_DAWN_COMMON_COMPILER_H_

// Defines macros for compiler-specific functionality
//  - DAWN_COMPILER_IS(CLANG|GCC|MSVC): Compiler detection
//  - DAWN_BUILTIN_UNREACHABLE(): Hints the compiler that a code path is unreachable
//  - DAWN_(UN)?LIKELY(EXPR): Where available, hints the compiler that the expression will be true
//      (resp. false) to help it generate code that leads to better branch prediction.
//  - DAWN_UNUSED(EXPR): Prevents unused variable/expression warnings on EXPR.
//  - DAWN_UNUSED_FUNC(FUNC): Prevents unused function warnings on FUNC.
//  - DAWN_DECLARE_UNUSED:    Prevents unused function warnings a subsequent declaration.
//  Both DAWN_UNUSED_FUNC and DAWN_DECLARE_UNUSED may be necessary, e.g. to suppress clang's
//  unneeded-internal-declaration warning.

// Clang and GCC, check for __clang__ too to catch clang-cl masquarading as MSVC
#if defined(__GNUC__) || defined(__clang__)
#if defined(__clang__)
#define DAWN_COMPILER_IS_CLANG 1
#else
#define DAWN_COMPILER_IS_GCC 1
#endif

#define DAWN_BUILTIN_UNREACHABLE() __builtin_unreachable()
#define DAWN_LIKELY(x) __builtin_expect(!!(x), 1)
#define DAWN_UNLIKELY(x) __builtin_expect(!!(x), 0)

#if !defined(__has_cpp_attribute)
#define __has_cpp_attribute(name) 0
#endif

#define DAWN_DECLARE_UNUSED __attribute__((unused))
#if defined(NDEBUG)
#define DAWN_FORCE_INLINE inline __attribute__((always_inline))
#endif
#define DAWN_NOINLINE __attribute__((noinline))

// MSVC
#elif defined(_MSC_VER)
#define DAWN_COMPILER_IS_MSVC 1

#define DAWN_BUILTIN_UNREACHABLE() __assume(false)

#define DAWN_DECLARE_UNUSED
#if defined(NDEBUG)
#define DAWN_FORCE_INLINE __forceinline
#endif
#define DAWN_NOINLINE __declspec(noinline)

#else
#error "Unsupported compiler"
#endif

// Attribute related macros based on Chromium's version in:
//   base/compiler_specific.h
#if defined(__has_attribute)
#define DAWN_HAS_ATTRIBUTE(x) __has_attribute(x)
#else
#define DAWN_HAS_ATTRIBUTE(x) 0
#endif

// Sanitizers annotations.
#if DAWN_HAS_ATTRIBUTE(no_sanitize)
#define DAWN_NO_SANITIZE(what) __attribute__((no_sanitize(what)))
#endif
#if !defined(DAWN_NO_SANITIZE)
#define DAWN_NO_SANITIZE(what)
#endif

// This section defines other compiler macros to 0 to avoid undefined macro usage error.
#if !defined(DAWN_COMPILER_IS_CLANG)
#define DAWN_COMPILER_IS_CLANG 0
#endif
#if !defined(DAWN_COMPILER_IS_GCC)
#define DAWN_COMPILER_IS_GCC 0
#endif
#if !defined(DAWN_COMPILER_IS_MSVC)
#define DAWN_COMPILER_IS_MSVC 0
#endif

// Use #if DAWN_COMPILER_IS(XXX) for compiler specific code.
// Do not use #ifdef or the naked macro DAWN_COMPILER_IS_XXX.
// This can help avoid common mistakes like not including "Compiler.h" and falling into unwanted
// code block as usage of undefined macro "function" will be blocked by the compiler.
#define DAWN_COMPILER_IS(X) (1 == DAWN_COMPILER_IS_##X)

// It seems that (void) EXPR works on all compilers to silence the unused variable warning.
#define DAWN_UNUSED(EXPR) (void)EXPR
// Likewise using static asserting on sizeof(&FUNC) seems to make it tagged as used
#define DAWN_UNUSED_FUNC(FUNC) static_assert(sizeof(&FUNC) == sizeof(void (*)()))

// Add noop replacements for macros for features that aren't supported by the compiler.
#if !defined(DAWN_LIKELY)
#define DAWN_LIKELY(X) X
#endif
#if !defined(DAWN_UNLIKELY)
#define DAWN_UNLIKELY(X) X
#endif
#if !defined(DAWN_FORCE_INLINE)
#define DAWN_FORCE_INLINE inline
#endif
#if !defined(DAWN_NOINLINE)
#define DAWN_NOINLINE
#endif

#endif  // SRC_DAWN_COMMON_COMPILER_H_