Currently, allocated memory is freed by calling the library function
_gfortran_internal_free, which does nothing but:
/* Free internally allocated memory. Pointer is NULLified. Also used to
free user allocated memory. */
void
internal_free (void *mem)
{
if (mem != NULL)
free (mem);
}
Two things are worth noting:
+ although the comment says otherwise, the pointer is not NULLified.
+ this code could be generated directly by the front-end, leading to better
optimization.
An example of the missed optimization is the compilation of the following code:
REAL :: a(5), b
INTEGER :: l, u
l = 4
u = 2
a = (/ 1.0, 2.0, 3.0, 4.0, 5.0 /)
b = f(a(l:u) - 3.0)
call foo(b)
CONTAINS
REAL FUNCTION f(x)
REAL, DIMENSION(:), INTENT(in) :: x
f = sum(x)
end function
END PROGRAM
the optimized tree looks like:
SR.33 = _gfortran_internal_malloc (0);
b = 0.0;
_gfortran_internal_free (SR.33);
We sure could optimize away the use of SR.33. PR 30720 has another case where
such an optimization could happen.
--
Summary: Freeing memory doesn't need to call a library function
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: fxcoudert at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30723
