This part of the gcc manual is pretty obscure and i can't understand the usage of the forceinline attribute after repeated attempts.
I'm defining an object and certain functions to manipulate that object. Few of those functions can use atomic instructions and i want the compiler to inline those functions. However i do not want to write those functions in the header file and declare them with "static inline" like in the linux kernel.
Is there a way to force gcc to inline functions from another translation unit ?
you can use the always_inline attribute, for example:
void foo () __attribute__((always_inline));
From the docs
always_inline Generally, functions are not inlined unless optimization is specified. For functions declared inline, this attribute inlines the function even if no optimization level was specified.
Note1: There's no need to use inline if you use the always_inline attribute
Note2: If the function could not be inlined you will get a warning, if for example the definition is not available when compiling, however, at a higher optimization gcc can still inline it into the caller, there's a specific switch for that too:
-funit-at-a-time
From the docs:
Optimization levels -O2 and above, in particular, enable unit-at-a-time mode, which allows the compiler to consider information gained from later functions in the file when compiling a function. Compiling multiple files at once to a single output file in unit-at-a-time mode allows the compiler to use information gained from all of the files when compiling each of them.
Note3: It is not necessary to have an explicit prototype so you can use the attribute on the function defintion:
__attribute__((always_inline)) void foo() {
//some code
}
Also see this discussion, it answers some of your questions.