These are found by adding -Winline on gcc. The flag is accepted on clang for compatibility with gcc, but it doesn't do anything.

Mostly, this removes inline from the declarations. For local static functions, there is no point in adding inline. This stems from either a misunderstanding of what it means, or alternatively is a holdover from ancient times where it may have meant something (note it still means something in a header file, but not a source file). A compiler is free to inline a static function, and specifying inline doesn't make the compiler inline the function. These pointless inlines make it harder to analyze failed inlining, so I remove them.

However, for select functions, this changes them to zend_always_inline instead. This is because these functions didn't inline, but probably should for performance reasons. For instance, _class_exists_impl is used in multiple frameless function handlers. I think in these cases, the authors were hoping they'd be inlined due to fact that are important for performance. There's also _php_search_array, which is used with constant args on a variety of functions. It fails to inline due to its size, but if it did inline, it would cut large amounts of code out, so forcing the inlining seemed worth it.

There's also i_get_exception_base which was removed. Again, the compiler is free to inline zend_get_exception_base if it wants to, and static inline doesn't make the compiler inline it. This function often failed to inline in my -Winline report. Alternatively this could be made zend_always_inline, but since this is related to exceptions--which are supposed to be rare to begin with--it seemed more prudent to not force the compiler to inline it.

This work is split out from #15075, so that's why it might seem like déjà vu.

There are still some -Winline failures, but they are in things I'd prefer not to change such as pcre or xxhash.