So, it seems that at some point in the past, the option
-fmax-stack-var-size was expanded to allow the placement
of an allocatable array into static memory. This has
a possibly unintended consequence in that automatic
deallocation of an allocatable array does not (or can
not) occur.
program foo
implicit none
call testAutoDealloc(20)
call testAutoDealloc(200)
contains
subroutine testAutoDealloc(n)
integer, intent(in) :: n
real, allocatable :: temp(:)
allocate(temp(n))
temp = n
if (temp(n) /= n) stop n
end
end program foo
% gfcx -o u a.f90 && ./u
% gfcx -o u -fmax-stack-var-size=10 -fdump-tree-original a.f90 && ./u
At line 9 of file a.f90
Fortran runtime error: Attempting to allocate already allocated variable 'temp'
% head -4 u-a.f90.005t.original
__attribute__((fn spec (". r ")))
void testautodealloc (integer(kind=4) & restrict n)
{
static struct array01_real(kind=4) temp = {.data=0B};
Now, it seems that an explicit deallocation of temp at the end of
the subroutine testAutoDealloc suppresses the runtime error. Looking
at a -fdump-tree-original with the modified code shows
if ((real(kind=4)[0:] * restrict) temp.data == 0B)
{
_gfortran_runtime_error_at (...Attempt to DEALLOCATE unallocated...);
}
else
{
__builtin_free ((void *) temp.data);
(real(kind=4)[0:] * restrict) temp.data = 0B;
}
Should the automatic deallocation of allocatable arrays be restore?
I'll let someone who cares enough to pursue this route. Until then,
here's a patch to the manual to caution the unwary.
diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index 6435dc4d4de..b5002d2a31a 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -1786,13 +1786,19 @@ The default value for @var{n} is 65535.
@item -fmax-stack-var-size=@var{n}
@opindex @code{fmax-stack-var-size}
This option specifies the size in bytes of the largest array that will be put
-on the stack; if the size is exceeded static memory is used (except in
-procedures marked as RECURSIVE). Use the option @option{-frecursive} to
-allow for recursive procedures which do not have a RECURSIVE attribute or
-for parallel programs. Use @option{-fno-automatic} to never use the stack.
+on the stack. If the size of an array exceeds @var{n}, then the array is
+placed in static memory (except in procedures marked as RECURSIVE). Use
+the option @option{-frecursive} to allow for recursive procedures which
+do not have a RECURSIVE attribute or for parallel programs.
+Use @option{-fno-automatic} to never use the stack.
+
+The @option{-Wsurprising} option can be used to determine which arrays
+have been placed into static memory.
+
+@option{-fmax-stack-var-size} can inhibit the automatic deallocation of
+allocatable arrays. Proper memory management is required if this option
+is used (i.e., explicit deallocation is encouraged).
-This option currently only affects local arrays declared with constant
-bounds, and may not apply to all character variables.
Future versions of GNU Fortran may improve this behavior.
The default value for @var{n} is 65536.
--
Steve
