From dd62fb6eeb9a5bc9a870430a93c6de1aca4be1d6 Mon Sep 17 00:00:00 2001
From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Date: Sun, 3 Oct 2021 14:03:25 +0200
Subject: [PATCH 01/21] avutil/avassert: Add av_unreachable and av_assume()
 macros

Useful to let the compiler and static analyzers know that
something is unreachable without adding an av_assert
(which would be either dead for the compiler or add runtime
overhead) for this.
The implementation used here enforces the use of a message
to provide a reason why a particular code is supposed to be
unreachable.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 doc/APIchanges       |  3 +++
 libavutil/avassert.h | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/doc/APIchanges b/doc/APIchanges
index 75d66f87f3..78dcaa8009 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2025-03-28
 
 API changes, most recent first:
 
+2025-05-06 - xxxxxxxxxx - lavu 60.xx.100 - avassert.h
+  Add av_unreachable() and av_assume() macros.
+
 2025-04-21 - xxxxxxxxxx - lavu 60.2.100 - log.h
   Add AV_CLASS_CATEGORY_HWDEVICE.
 
diff --git a/libavutil/avassert.h b/libavutil/avassert.h
index 1895fb7551..d0d5aa0c7e 100644
--- a/libavutil/avassert.h
+++ b/libavutil/avassert.h
@@ -31,6 +31,7 @@
 #ifdef HAVE_AV_CONFIG_H
 #   include "config.h"
 #endif
+#include "attributes.h"
 #include "log.h"
 #include "macros.h"
 
@@ -75,4 +76,45 @@
  */
 void av_assert0_fpu(void);
 
+/**
+ * Asserts that are used as compiler optimization hints depending
+ * upon ASSERT_LEVEL and NBDEBUG.
+ *
+ * Undefined behaviour occurs if execution reaches a point marked
+ * with av_unreachable() or if a condition used with av_assume()
+ * is false.
+ *
+ * The condition used with av_assume() should not have side-effects
+ * and should be visible to the compiler.
+ */
+#if defined(ASSERT_LEVEL) ? ASSERT_LEVEL > 0 : !defined(HAVE_AV_CONFIG_H) && !defined(NDEBUG)
+#define av_unreachable(msg)    \
+do {                           \
+    av_log(NULL, AV_LOG_PANIC, \
+           "Code at %s:%d that was supposedly unreachable due to '%s' reached\n", \
+           __FILE__, __LINE__, msg); \
+    abort();                   \
+} while (0)
+#define av_assume(cond) av_assert0(cond)
+#else
+#if AV_GCC_VERSION_AT_LEAST(4, 5) || AV_HAS_BUILTIN(__builtin_unreachable)
+#define av_unreachable(msg) __builtin_unreachable()
+#elif  defined(_MSC_VER)
+#define av_unreachable(msg) __assume(0)
+#define av_assume(cond)     __assume(cond)
+#elif __STDC_VERSION__ >= 202311L
+#include <stddef.h>
+#define av_unreachable(msg) unreachable()
+#else
+#define av_unreachable(msg) ((void)0)
+#endif
+
+#ifndef av_assume
+#define av_assume(cond) do { \
+    if (!(cond))             \
+        av_unreachable();    \
+} while (0)
+#endif
+#endif
+
 #endif /* AVUTIL_AVASSERT_H */
-- 
2.45.2