[FFmpeg-devel] MPEG-2 Acceleration Refactor

[Trent Piepho]

On Fri, 22 Jun 2007, Michael Niedermayer wrote:
> if yes then this is a new gcc bug, that is gcc inlines fewer functions
> with av_always_inline but there is not a single function it inlines in the
> av_always_inline case which wasnt already inlined wthout it
>
> if no and the normal inline case looks different then this is still a
> gcc bug just not a new one, av_always_inline should IMO inline the function
> without changing the inlining of the other code (if av_inline behaves
> different, which it does sadly, then its not usefull for anything and
> another attribute which does force the inlining of a function without
> code slowification sideeffectes would be needed)

gcc will do a lot of inlining without any kind of inline keywords or
attributes at all.  There are a number of parameters that control this.

Imagine three functions, A which calls B which calls C.  One could inline B
into A, but not inline C into A+B.  Or inline C into B, but not inline B+C
into A.  Or inline all three.

Suppose functions A and B are small, but C is big.

In one inline directives are used, gcc might decide to inline B into A, but
not inline C.  If you now add an inline directive to C, gcc will inline C into
B, and the new big B+C function won't be inlined into A.