flatten function attribute

Joe Guest 2010-08-05 19:00 #1807570

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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.

void test_flatten(void) __attribute__((flatten));
void test_flatten(void){
    function1();
    function2();


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.

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Joe D. (jdupre) 2010-08-05 19:04 #1807574

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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.

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Rolf Magnus Guest 2010-08-05 20:11 #1807660

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> 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.

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Joe D. (jdupre) 2010-08-10 21:18 #1813424

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

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Prakash Guest 2020-05-24 12:59 #6276597

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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++;
    }
}

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Rolf Magnus Guest 2020-05-24 17:11 #6276891

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

void hot_code() __attribute__((flatten));

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