Test the Stack memory bias for Fortran allocatable/pointer variables

Fortran_Stack_Bias.md

Test Fortran Satck Memory Bias

A testbased on Gary Scott's issue described here.

This test reproduction is devoted to Paul Rich & Co. for GNU gfortran users

The test code

program test
use iso_fortran_env

implicit none

type WPDataDef
  real(real32), pointer     :: selData(:,:)
  real(real32), pointer     :: selDataG(:,:)
  real(real32), allocatable :: set1Data(:,:)
  real(real32), allocatable :: set2Data(:,:)
  real(real32), allocatable :: set3Data(:,:)
end type

type (WPDataDef), target :: svWPData
type (WPDataDef)         :: wpDataSort

allocate(svWPData%set1Data(600,5000))
allocate(svWPData%set2Data(600,5000))
allocate(svWPData%set3Data(600,5000))

allocate(WPDataSort%set1Data(600,5000))

#ifdef STACK
svWPData%set1Data = wpDataSort%set1Data
#else
call safe_copy(to=svWPData%set1Data, from=wpDataSort%set1Data)
#endif

contains
  subroutine safe_copy(from, to)
    real(real32), intent(in)  :: from(:,:)
    real(real32), intent(out) :: to(:,:)
    to = from
  end subroutine safe_copy
end program

Running Architecture

Lenovo MIIX 700, Intel(R) Core(TM) m5-6Y54 CPU @ 1.10GHz, 4GB Ram, 4.4.0-45-generic #66-Ubuntu SMP Wed Oct 19 14:12:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Results

stefano@thor(08:21 AM Sun Nov 06)
~/downloads/test_stack 2 files, 28Kb
→ gfortran -DSTACK -Warray-temporaries test_stack.F90 

stefano@thor(08:28 AM Sun Nov 06)
~/downloads/test_stack 2 files, 28Kb
→ ./a.out 

stefano@thor(08:28 AM Sun Nov 06)
~/downloads/test_stack 2 files, 28Kb
→ gfortran -Warray-temporaries test_stack.F90 

stefano@thor(08:28 AM Sun Nov 06)
~/downloads/test_stack 2 files, 28Kb
→ ./a.out 

Compiler

GNU gfortran 6.2.0

Stack memory

ulimit -s 1024

Conclusions

Under GNU Linux, with GNU gfortran 6.2.0 the test shows that the stack memory is not used as expected, the stack memory being also reduced to 1MB.