Re: [avr-gcc-list] Space optimisation for PSTR()

[E. Weddington]

Bernard Fouché wrote:

> Yeah I was wrong in the parenthesis places but you got the point.
>
> I asked this question because I thought that compilers were used to optimise
> strings that way.
>
> Thanks for your answer
>
>  

Yes compilers *can* be used in this way, and certain compilers (most) do 
this.

The main problem here is that the AVR is a Harvard Architecutre device, 
with separate Program Address Space and Data Address Space. The current 
C Standard does not have anything to account for different address 
spaces, and consequently GCC does not know anything about it either. 
From what I understand, is that there are drafts out there that will 
correct the C Standard to help address this issue. We know of one AVR 
developer (Svein Seldal) who is trying to patch GCC to get it to know 
about different address spaces. This is a very huge task. Probably when 
this happens then additional opimisation can be added to combine 
references to identical strings that reside in the program space. Until 
this happens, you'll have to manage your own strings. Sorry. :-(

Eric