Double allocation error in mesh3d.F90

[Yann Pouillon]

In the trunk branch, for revnos > 740 (I didn't go earlier), if I compile SIESTA with GCC and the following FFLAGS for debugging:

    -g3 -ggdb -fPIC -fbacktrace -fcheck=bounds,do,mem,pointer,recursion -fimplicit-none -finit-real=snan -fno-automatic -fno-omit-frame-pointer -O0

I get a runtime error about the nodeboxes array in SiestaXC/mesh3d.F90:

    At line 2992 of file /home/pouillon/siesta/honpas/siesta-honpas/Src/SiestaXC/mesh3d.F90
    Fortran runtime error: Attempting to allocate already allocated variable 'nodeboxes'

GCC 5.4, 6.3 and 6.4 give me the same error, while other compilers with equivalent flags don't detect it. Without the -fcheck and -fno-automatic flags, the error disappears.

The attached patch fixes this minor issue.

[Nick Papior (nickpapior)]

Having a 2nd look at the code, it may be even easier to delete the `nodesBoxes`, i.e. something like this:

=== modified file 'Src/SiestaXC/mesh3d.F90'
--- Src/SiestaXC/mesh3d.F90 2017-02-17 13:28:06 +0000
+++ Src/SiestaXC/mesh3d.F90 2018-12-14 10:29:28 +0000
@@ -2926,7 +2926,7 @@
   character(len=*),parameter:: errHead = myName//'ERROR: '
   integer, parameter:: maxFactors = 100 ! Max prime factors in nNodes
   type(distrType),pointer:: distr, newDistr, oldDistr
- integer,allocatable:: axisBox(:,:,:), nodeBoxes(:,:,:), partBox(:,:,:)
+ integer,allocatable:: axisBox(:,:,:), partBox(:,:,:)
   integer:: axis, axisNodes(3), blockSize, boxSize, &
             factor(maxFactors), groupSize, &
             i1, i2, i3, iAxis, iBox, iDistr, iFac, iID, iNode, iPow, &
@@ -2989,9 +2989,7 @@
 ! Handle box argument with priority
   if (present(box)) then
     ! Collect all node boxes and store them
- allocate( nodeBoxes(2,3,0:totNodes-1) )
- call gatherBoxes( box, nodeBoxes )
- distr%box = nodeBoxes
+ call gatherBoxes( box, distr%box )
     goto 999 ! Exit, since no other arguments must be considered in this case
   end if ! (present(box))

[Yann Pouillon (pouillon)]

Sure, that's also what I would have done. I only proposed a minimalistic patch because I didn't know about your intentions regarding the variable nor the possible side effects in LibGridXC.

[Alberto Garcia (albertog)]

In f95 and later, non-saved local (to a routine) allocatable arrays must be allocated on exit from the routine. This is why the use of '-fno-automatic' triggers the bug, but every other (modern) compilation fails to detect it.
Despite requiring de facto a f2003 compiler, I guess we should guard against these kind of standard-flavor-dependent issues by being more conservative. In this case, by explicit deallocation of the array.
I wonder if there are enough compiler flags to detect more complicated issues.

[Alberto Garcia (albertog)]

Of course, I meant "must be DEallocated on exit..." in the above comment.