EmbDev.net

Forum: ARM programming with GCC/GNU tools flatten function attribute


flatten function attribute
von Joe (Guest)

Rate this post
• ▲ useful
▼ not useful 
Has anyone had success with __attribute__((flatten)) using yagarto?

I have tried various locations of the attribute tag in the function 
declaration or definition, but it appears the attribute is completely 
ignored.

1
void test_flatten(void) __attribute__((flatten));

2
3
void test_flatten(void){

4
    function1();

5
    function2();

6
}


From what I understand, flatten is supposed to "inline" all calls within 
a function, essentially creating one large "stand-alone" function.  When 
I step through the supposedly flattened code, there are still "bl" 
instructions to function1() and function2() locations.

  


  




  

    Report post Edit Move Thread sperren Anmeldepflicht aktivieren Anpinnen Delete topic Thread mit anderem zusammenführen Quote selected text Reply Reply with quote
  







      

      



  

    Re: flatten function attribute
  


  

    

      von
      
        Joe D.
        (jdupre)
        
      
      


      
    


    

      
    

    

    

  
  


  

  Rate this post
  

  •
  
  ▲ useful 
  

  ▼ not useful 
  		
  

  


  

      
I should add that the docs say "The flatten attribute only works 
reliably in unit-at-a-time mode. ", which should be enabled with 
optimization -O1. But I still get don't get the single monolithic block 
of code I expect, there are still branches to the other functions.

  


  




  

    Report post Edit Delete Quote selected text Reply Reply with quote
  







      

      



  

    Re: flatten function attribute
  


  

    

      von
      
        Rolf Magnus (Guest)
      
      


      
    


    

      
    

    

    

  
  


  

  Rate this post
  

  •
  
  ▲ useful 
  

  ▼ not useful 
  		
  

  


  

      
> From what I understand, flatten is supposed to "inline" all calls within
> a function

... "if possible". Did you define those two functions in the same 
implementation file as your test_flatten function? If they are 
implemented in a different one, they can't be inlined.

  


  




  

    Report post Edit Delete Quote selected text Reply Reply with quote
  







      

      



  

    Re: flatten function attribute
  


  

    

      von
      
        Joe D.
        (jdupre)
        
      
      


      
    


    

      
    

    

    

  
  


  

  Rate this post
  

  •
  
  ▲ useful 
  

  ▼ not useful 
  		
  

  


  

      
No.  One of the functions was in a different file.

  


  




  

    Report post Edit Delete Quote selected text Reply Reply with quote
  







      

      



  

    Re: flatten function attribute
  


  

    

      von
      
        Prakash (Guest)
      
      


      
    


    

      
    

    

    

  
  


  

  Rate this post
  

  •
  
  ▲ useful 
  

  ▼ not useful 
  		
  

  


  

      
Hi,

I am using GCC version 9 in Ubuntu 14.04

I have defined two function in the same file and one of the function is 
attributed as "flatten" but But I still did not get the single 
monolithic block of code I expect, there are still branches to the other 
functions.

Why exactly it is not following the flatten attribute concept ?

Here is the code

void __attribute__((flatten)) hot_code();

void do_thing(int input)
{
    int val;
    val = input;
}

void __attribute__((flatten)) hot_code()
{
    int x = 5;
    while (x<10) {
        do_thing(x);
        x++;
    }
}

  


  




  

    Report post Edit Delete Quote selected text Reply Reply with quote
  







      

      



  

    Re: flatten function attribute
  


  

    

      von
      
        Rolf Magnus (Guest)
      
      


      
    


    

      
    

    

    

  
  


  

  Rate this post
  

  •
  
  ▲ useful 
  

  ▼ not useful 
  		
  

  


  

      
Prakash wrote:
> void __attribute__((flatten)) hot_code();

1
void hot_code() __attribute__((flatten));


  


  




  

    Report post Edit Delete Quote selected text Reply Reply with quote
  








    

    

       Watch this topic

      |
         Disable multi-page view

    

        


Please log in before posting. Registration is free and takes only a minute.



  Existing account

  


  
  

  
    

      

        
          
        
        
          
        
      

      

        
          
        
        
          
        
      

    


    
    
    





  Do you have a Google/GoogleMail account? No registration required!

  Log in with Google account
  





  No account? Register here.