Some software (often performance-oriented, e.g. Linux kernel, DPDK) has C helpers for influencing branch prediction. I have an absolutely simple code snippet (suppose I know the percantage of a &gt...

IN SHORT: Is there a place to put the [[(un)likely]] attribute so that the control flow at cond2 is considered likely to take the false branch, without affecting the possibility of branches at cond...

GCC compiler supports __builtin_expect statement that is used to define likely and unlikely macros. eg. #define likely(expr) (__builtin_expect(!!(expr), 1)) #define unlikely(expr) (__builtin_expe...

I came across a #define in which they use __builtin_expect. The documentation says: Built-in Function: long __builtin_expect (long exp, long c) You may use __builtin_expect to provide the co...

This question is about C++20's [[likely]]/[[unlikely]] feature, not compiler-defined macros. This documents (cppreference) only gave an example on applying them to a switch-case statement. This sw...

How can I demonstrate for students the usability of likely and unlikely compiler hints (__builtin_expect)? Can you write an sample code, which will be several times faster with these hints compari...

C++20 introduced the attributes [[likely]] and [[unlikely]] to the language, which can be used to allow the compiler to optimize for the case where one execution path is either much more likely or ...

In my objdump -t output, I see the following two lines: 00000000000004d2 l F .text.unlikely 00000000000000ec function-signature-goes-here [clone .cold.427] and 00000000000018e0 g F .text 000000...

I often find myself writing a code that looks something like this: if(a == nullptr) throw std::runtime_error("error at " __FILE__ ":" S__LINE__); Should I prefer handling errors with if unlikely...

I've been digging through some parts of the Linux kernel, and found calls like this: if (unlikely(fd < 0)) { /* Do something */ } or if (likely(!err)) { /* Do something */ } I've found the d...

If I have: #define likely(x) __builtin_expect((x),1) #define unlikely(x) __builtin_expect((x),0) if (A) return true; else if (B) return false; ... else if (Z) return true; else //this will ne...

I am writing a critical piece of code with roughly the following logic if(expression is true){ //do something with extremely low latency before the nuke blows up. This branch is entered rarely, b...

Just see this construction in the linux kernel, and I can't get what does it mean. 110 return unlikely(sl->sequence != start); I know that likely/unlikely are made with __builtin_expect funct...

I came across these 2 macros in Linux kernel code. I know they are instructions to compiler (gcc) for optimizations in case of branching. My question is, can we use these macros in user space code?...