From 26a029d407be480d791972afb5975cf62c9360a6 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Fri, 19 Apr 2024 02:47:55 +0200 Subject: Adding upstream version 124.0.1. Signed-off-by: Daniel Baumann --- third_party/libwebrtc/rtc_base/system/assume.h | 73 ++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 third_party/libwebrtc/rtc_base/system/assume.h (limited to 'third_party/libwebrtc/rtc_base/system/assume.h') diff --git a/third_party/libwebrtc/rtc_base/system/assume.h b/third_party/libwebrtc/rtc_base/system/assume.h new file mode 100644 index 0000000000..231c9e18ad --- /dev/null +++ b/third_party/libwebrtc/rtc_base/system/assume.h @@ -0,0 +1,73 @@ +/* + * Copyright (c) 2020 The WebRTC project authors. All Rights Reserved. + * + * Use of this source code is governed by a BSD-style license + * that can be found in the LICENSE file in the root of the source + * tree. An additional intellectual property rights grant can be found + * in the file PATENTS. All contributing project authors may + * be found in the AUTHORS file in the root of the source tree. + */ + +#ifndef RTC_BASE_SYSTEM_ASSUME_H_ +#define RTC_BASE_SYSTEM_ASSUME_H_ + +// Possibly evaluate `p`, promising the compiler that the result is true; the +// compiler is allowed (but not required) to use this information when +// optimizing the code. USE WITH CAUTION! If you promise the compiler things +// that aren't true, it will build a broken binary for you. +// +// As a simple example, the compiler is allowed to transform this +// +// RTC_ASSUME(x == 4); +// return x; +// +// into this +// +// return 4; +// +// It is even allowed to propagate the assumption "backwards in time", if it can +// prove that it must have held at some earlier time. For example, the compiler +// is allowed to transform this +// +// int Add(int x, int y) { +// if (x == 17) +// y += 1; +// RTC_ASSUME(x != 17); +// return x + y; +// } +// +// into this +// +// int Add(int x, int y) { +// return x + y; +// } +// +// since if `x` isn't 17 on the third line of the function body, the test of `x +// == 17` on the first line must fail since nothing can modify the local +// variable `x` in between. +// +// The intended use is to allow the compiler to optimize better. For example, +// here we allow the compiler to omit an instruction that ensures correct +// rounding of negative arguments: +// +// int DivBy2(int x) { +// RTC_ASSUME(x >= 0); +// return x / 2; +// } +// +// and here we allow the compiler to possibly omit a null check: +// +// void Delete(int* p) { +// RTC_ASSUME(p != nullptr); +// delete p; +// } +// +// clang-format off +#if defined(__GNUC__) +#define RTC_ASSUME(p) do { if (!(p)) __builtin_unreachable(); } while (0) +#else +#define RTC_ASSUME(p) do {} while (0) +#endif +// clang-format on + +#endif // RTC_BASE_SYSTEM_ASSUME_H_ -- cgit v1.2.3