[avr-gcc-list] Re: optimizer removes volatile pin access code. why?

[David Brown]

Stu Bell wrote:
> David Brown wrote:
>  
> > And an __attribute_((always_inline)) function will be 
> > inlined, regardless of the optimisation levels.
>
> Sorry, compiler breath -- this is not always true.  If you call an
> "always_inline" function from inside another "always_inline" function,
> with optimization turned off, the compiler throws a fit.  
>
> Example -- WinAVR 20090313, file compiled with -O0.  Inline function is:
>
> static void
> FcsStartUtilTimer( uint16_t Wait ) __attribute__((always_inline));
> static void
> FcsStartUtilTimer( uint16_t Wait ) 
> {

<snip>

> Returns the following error:
>
> CmdFocus.c: In function 'FcsAcquireLookForSumOKDeassert':
> CmdFocus.c:4020: sorry, unimplemented: inlining failed in call to
> 'FcsStartUtilTimer': function body not available
> CmdFocus.c:4152: sorry, unimplemented: called from here
> ...

That's hardly "throwing a fit" - it's simply telling you it can't obey 
the "always_inline" attribute.

However, I think the problem stems from a misunderstanding about 
"always_inline" - it's an /additional/ request to the compiler that you 
can use for /inline/ functions.  From the gcc documentation:

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.


If you declare your functions "inline", it should work as you desire 
even with -O0:

static inline void
FcsStartUtilTimer( uint16_t Wait ) __attribute__((always_inline));
static inline void
FcsStartUtilTimer( uint16_t Wait )


mvh.,

David


> The above code compiles fine if the optimizer is turned on (-Os).  Of
> course, I guess the real question (which I have not investigated) is
> whether it compiles *correctly* with -Os. :-/  It functions correctly,
> so I presume it is inlining correctly.
>
> Best regards, 
>
> Stu Bell 
> DataPlay (DPHI, Inc.)