[Patch, fortran] PR61831 side-effect deallocation of variable components

[Mikael Morin]

Le 16/05/2015 18:43, Mikael Morin a écrit :
> Hello,
> 
> this is about PR61831 where in code like:
> 	
> 	type :: string_t
> 	   character(LEN=1), dimension(:), allocatable :: chars
> 	end type string_t
> 	type(string_t) :: prt_in
> 	(...)
> 	tmp = new_prt_spec ([prt_in])
> 	
> the deallocation of the argument's allocatable components after the
> procedure call (to new_prt_spec) has the side effect of freeing prt_in's
> allocatable components, as the array constructor temporary for [prt_in]
> is a shallow copy of prt_in.
> 
> This bug is a regression caused by the Dominique's PR41936 memory leak
> fix, itself based on a patch originally from me.
> 
> The attached patch is basically a revert of that fix.  It avoids the
> problem by not deallocating allocatable components in the problematic
> case, at the price of a (possible) memory leak.  A new function is
> introduced telling whether there is aliasing, so that we don't regress
> on PR41936's memory leak when there is no aliasing, and we don't free
> components when there is aliasing.
> The possible remaining memory leak case is the case of a "mixed" array
> constructor with some parts aliasing variables, and some non-aliasing parts.
> 
> The patch takes also the opportunity to reassemble the scattered
> procedure argument deallocation code into a single place.
> 
> The test needs pr65792's fix (thanks Paul), so for the 4.9 branch I
> propose commenting the parts that depend on PR65792 in the test.
> 
> Regression tested on x86_64-linux. OK for 6/5/4.9 ?

Hello,

I would like to come back to the patch:
https://gcc.gnu.org/ml/gcc-patches/2015-05/msg01491.html

PR66082 made me notice one bug in that patch:
for descriptorless arrays, the patch was deallocating only the first
element's allocatable components.
As gfc_conv_array_parameter returns the array data only, the bounds are
lost and it is not possible to loop through all the elements.

With the attached patch, the deallocation code is kept in
gfc_conv_array_parameter where the bounds of descriptorless arrays are
known.
To test this fixes the bug, I have added a count of while (1) loops in
the dump of pr66082's test.  I'm open to better ideas to properly test this.

For arrays with descriptors, I have decided to not handle them in
gfc_conv_array_parameter, because in some cases gfc_conv_expr_descriptor
is called directly from gfc_conv_procedure_call, without passing through
gfc_conv_array_parameter.
To be able to select everything but descriptorless arrays for
allocatable component deallocation, the flags are moved around somewhat.
The rest is as in the previous patch.

The test provided is basically unchanged, thus not suitable for the
branches without pr65792.
We can decide what to do with it later (backport pr65792 or disable
parts of the test), I would like to have the fix in mainline first.
It has been fortran-tested on x86_64-linux, OK for trunk?

Mikael



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2015-06-20  Mikael Morin  <mikael@gcc.gnu.org>
	    Dominique d'Humieres  <dominiq@lps.ens.fr>

	PR fortran/61831
	* trans-array.c (gfc_conv_array_parameter): Guard allocatable
	component deallocation code generation with descriptorless
	calling convention flag.
	* trans-expr.c (gfc_conv_expr_reference): Remove allocatable
	component deallocation code generation from revision 212329.
	(expr_may_alias_variables): New function.
	(gfc_conv_procedure_call): New boolean elemental_proc to factor
	check for procedure elemental-ness.  Rename boolean f to nodesc_arg
	and declare it in the outer scope.  Use expr_may_alias_variables,
	elemental_proc and nodesc_arg to decide whether generate allocatable
	component deallocation code.
	(gfc_trans_subarray_assign): Set deep copy flag.

2015-06-20  Mikael Morin  <mikael@gcc.gnu.org>

	PR fortran/61831
	* gfortran.dg/derived_constructor_components_6.f90: New.

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