Local arrays of variable size are allocated

Local arrays of variable size are allocated

[Alberto Luaces]

Hello,

in a procedure as

--8<---------------cut here---------------start------------->8---
subroutine name (size)
  integer, intent(in) :: size
  integer:: v(3, size)

  v(:,:) = 0
  
end subroutine name
--8<---------------cut here---------------end--------------->8---

I can see that "v" is allocated with malloc() on entry (and freed on
exit), instead of being mapped into the stack.

I imagine this is done in a general basis as a protection from stack
overflows, but in my case it is adding a significant overhead.

Can adjust anything so only stack space is used?

Thanks,

-- 
Alberto

Re: Local arrays of variable size are allocated

[Alberto Luaces]

Dominique d'Humières writes:

>> Spot on, Dominique! -Ofast triggers "-fstack-arrays", which does exactly
>> what I need.
>
> Beware of pr68829.
>

Thanks!  Yes, I imagined that the default was overly-conservative in
order to avoid stack overflows.  I will be watching for that, even my
arrays are pretty small.  That was the reason why I had a big overhead
in small, frequent-called functions.

-- 
Alberto

Re: Local arrays of variable size are allocated

[Dominique d'Humières]

> Spot on, Dominique! -Ofast triggers "-fstack-arrays", which does exactly
> what I need.

Beware of pr68829.

Dominique

> Le 13 avr. 2016 à 20:18, Dominique d'Humières <dominiq@lps.ens.fr> a écrit :
> 
>> Can adjust anything so only stack space is used?
> 
> Which options are you using? You may want to try -Ofast.
> 
> Dominique
> 

Re: Local arrays of variable size are allocated

[Alberto Luaces]

Dominique d'Humières writes:

>> Can adjust anything so only stack space is used?
>
> Which options are you using? You may want to try -Ofast.

Spot on, Dominique! -Ofast triggers "-fstack-arrays", which does exactly
what I need.

-- 
Alberto

Re: Local arrays of variable size are allocated

[Dominique d'Humières]

> Can adjust anything so only stack space is used?

Which options are you using? You may want to try -Ofast.

Dominique