gcc - __builtin_expect 来自 GCC 的概率

Question

程序员可以使用来自 GCC 的

__builtin_expect 来显示哪些变体预计会经常出现，哪些变体很少见。但是 __builtin_expect 只有“真”和“假”(0% 或 100% 概率)

对于一些大型项目，很难获得配置文件反馈(-fprofile-arcs)，有时程序员确实知道，他在程序的某个点有多大的分支概率。

可以提示编译器一个分支的概率 >0% 和 <100% 吗？

Answer 1

来自 here :

long __builtin_expect_with_probability

(long exp, long c, double probability) The function has the same semantics as __builtin_expect, but caller provides the expected probability that exp == c. Last argument, probability, is a floating-value in the inclusive range 0.0f and 1.0f. The probability argument must be constant floating-point expression.

Jesin 在评论中指出，Clang 11 has it too .