[avr-gcc-list] Re: Code optimistaion in AVR Tiny13

[David Brown]

Ruud Vlaming wrote:
> On Monday 16 February 2009 15:11, Robert von Knobloch wrote:
>
> > On inspection I find that the compiler has 'in-lined' at least 3
> > function calls that I had written as a function to achieve compactness.
> > Is there any way I can stop this, or is this a bug?
>
> There has been some discussions about this before. After trying many
> different optimization settings i concluded that
>   --param inline-call-cost=2 
> is -overall- the best setting for small projects. However, if you need to 
> minimize just one app, further reduction might be possible. 
> For example with things like:
>   -fno-inline-small-functions 
>   -fno-split-wide-types 
>   -fno-tree-scev-cprop 
>
> Also, you can prohibit the compiler to inline on a function by function basis.
>
> Just to be sure you have no dead code around, include:
>   -ffunction-sections -Wl,--gc-sections -Wl,--relax

An alternative to using -ffunction-sections is simply not to write extra 
functions - that should be easy enough for a small program!

One note about inlining - you should not disable all inlining, just 
limit automatic inlining of small functions (as you've done here). 
Automatic inlining of functions that are only used once is always a win 
in time and space.

Another important point in getting code as small as possible is to use 
-combine and -fwhole-program - it can significantly improve code, 
especially for functions that are called only once but live in different 
modules.