Hi everyone I'm new here. I read the mailing list policy, but please correct me if I'm doing anything wrong.
In our C codebase, we're using a fair amount of static inline __attribute__((always_inline)). This is arguably not a great decision, because it forces inlining under questionable conditions, i.e. in cold functions and unlikely branches. We're looking into switching some non-trivial functions to extern inline instead. When testing I noticed that GCC avoids inlining in __attribute__((cold)) functions, but not in unlikely branches, as signaled by __builtin_expect(cond, 0), even if the caller is hot. See https://godbolt.org/z/sxnYh5PsE. The unlikely branch is moved to the bottom, but it still seems beneficial to avoid inlining to reduce instruction cache pressure for the rest of the hot functions. I wasn't able to achieve this behavior with __builtin_expect or __builtin_expect_with_probability with a very high probability. Coincidentally, Clang does the exact opposite, inlining in cold functions, but not in unlikely branches. This is just one example, and I don't know anything about the heuristics GCC uses to determine if some function is inlined. I wanted to bring this up nonetheless to see if this situation may be improved. I wasn't sure if this belongs in the bug tracker, let me know if I should move it there instead. Thank you. Ilija
