https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114262
Bug ID: 114262 Summary: Over-inlining when optimizing for size? Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: lh_mouse at 126 dot com Target Milestone: --- (https://gcc.godbolt.org/z/a4ox6oEfT) ``` struct impl; struct impl* get_impl(int key); int get_value(struct impl* p); extern __inline__ __attribute__((__gnu_inline__)) int get_value_by_key(int key) { struct impl* p = get_impl(key); if(!p) return -1; return get_value(p); } int real_get_value_by_key(int key) { return get_value_by_key(key); } ``` This is actually two functions, one is `gnu_inline` and the other is a non-inline one. It looks to me that if I mark a function `gnu_inline`, I assert that 'somewhere I shall provide an external definition for you' so when optimizing for size, GCC may generate a call instead of using the more complex inline definition. The `real_get_value_by_key` function is made a deliberate sibling call, so ideally this should be ``` real_get_value_by_key: jmp get_value_by_key ``` and not ``` real_get_value_by_key: push rsi call get_impl test rax, rax je .L2 mov rdi, rax pop rcx jmp get_value .L2: or eax, -1 pop rdx ret ``` It still gets inlined with `-finline-limit=0` and can only be disabled by `-fno-inline`. I have no idea how it is controlled. --------------------------- # Trivia These are two `gnu_inline` functions from the same library. Most of the time they should both be inlined in user code. However, external definitions are required when optimization is not turned on, or when their addresses are taken, so they must still exist. As they are unlikely to be used anyway, optimizing for size makes much more sense.