side effects of the compiler-generated calls

[David Livshin]

Tobias Schlüter wrote:
> David Livshin wrote:
>> Actually I hoped that as routines from the fortran library, they 
>> might have "simplified" calling convention, e.g. affect less  (  then 
>> normal calls ) resources ( registers ). As to the stack pointer, 
>> analyzing the compiler generated code, I didn't see any cases of 
>> stack-adjustment after the calls to these routines - the question is 
>> if I may assume it to be a rule; for what routines is it a rule?
>
> libgfortran is (for the most part) implemented in C, so it uses the C 
> ABI.  I had a quick look through the code to verify that no attributes 
> which may affect calling conventions are set.  I don't think you may 
> assume anything beyond that.
>
> From the description of your software it looks like you're the 
> assembly expert, so I may be wrong here, but I assume that you don't 
> see stack adjustments because as long as the compiler doesn't get 
> confused, it doesn't have to re-adjust the stack.  So instead of doing
>   push arg
>   push arg
>   call f
>   add %esp, ...
>   push arg
>   call g
>   add %esp, ...
> it can omit the first add, using a larger offset in the second add (or 
> sub, if I misremembered the stack growth direction).
>
> - Tobi
>
Normally stack cleanup is the responsibility of the caller, and normally 
it is not necessary as compiler uses "mov" instructions rather than 
"push"es to pass parameters on the stack. So it seems that my question 
is not fortran-specific but is more general, related to the gcc calling 
conventions.

Thank you for your help and assistance,

David

-- 
David Livshin

http://www.dalsoft.com