Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 73 insertions, 0 deletions

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_