Early PING for that patch.
On 06.09.21 12:52, Tobias Burnus wrote:
Hi all,
gfortran's internal array descriptor (xgfc descriptor) and
the descriptor used with BIND(C) (CFI descriptor, ISO_Fortran_binding.h
of TS29113 / Fortran 2018) are different. Thus, when calling a BIND(C)
procedure the gfc descriptor has to be converted to cfi – and when a
BIND(C) procedure is implemented in Fortran, the argument has to be
converted back from CFI to gfc.
The current implementation handles part in the FE and part in
libgfortran,
but there were several issues, e.g. PR101635 failed due to alias issues,
debugging wasn't working well, uninitialized memory was used in some
cases
etc.
This patch now moves descriptor conversion handling to the FE – which
also
can make use of compile-time knowledge, useful both for diagnostic and to
optimize the code.
Additionally:
- Some cases where TS29113 mandates that the array descriptor should be
used now use the array descriptor, in particular character scalars with
'len=*' and allocatable/pointer scalars.
- While debugging the alias issue, I simplified 'select rank'. While some
special case is needed for assumed-shape arrays, those cannot appear
when
the argument has the pointer or allocatable attribute. That's not
only a
missed optimization, pointer/allocatable arrays can also be NULL - such
that accessing desc->dim.ubound[rank-1] can be uninitialized memory ...
OK? Comments? Suggestions?
* * *
For some more dumps, see the discussion about the alias issue at:
https://gcc.gnu.org/pipermail/gcc-patches/2021-August/578364.html
("[RFH] ME optimizes variable assignment away / Fortran bind(C)
descriptor conversion")
plus the original emails:
- https://gcc.gnu.org/pipermail/gcc-patches/2021-August/578271.html
- and (correct dump)
https://gcc.gnu.org/pipermail/gcc-patches/2021-August/578274.html
Debugging - not ideal but not too bad either. For
subroutine f(x) bind(C)
integer :: x(:)
with an uninitialized size-4 array as argument:
m::f (_x=...) at foo4.f90:3
3 subroutine f(x) bind(C)
(gdb) p x
Cannot access memory at address 0x38
(gdb) p _x
$6 = ( base_addr = 0x7fffffffe2c0, elem_len = 4, version = 1, rank = 1
'\001', attribute = 2 '\002', type = 1025, dim = (( lower_bound = 0,
extent = 5, sm = 4 )) )
(gdb) s
5 x(1) = 5
(gdb) p x
$7 = (0, 0, 0, -670762413, 0)
Tobias
PS: This patch fixes but not necessarily fully the following PRs:
PR fortran/102086 - [F2008][TS29113] Accepts invalid scalar TYPE(*) as
actual argument to assumed-rank
PR fortran/92189 - Fortran-written bind(C) function with allocatable
argument does not update C descriptor on exit
PR fortran/92621 - Problems with memory handling with allocatable
intent(out) arrays with bind(c)
PR fortran/101308 - Bind(C): gfortran does not create C descriptors
for scalar pointer/allocatable arguments
PR fortran/101635 - FAIL: gfortran.dg/PR93963.f90 – alias-handling
issue with BIND(C)'s _gfortran_cfi_desc_to_gfc_desc
PR fortran/92482 - BIND(C) with array-descriptor mishandled for type
character
and possibly some more.
PPS: I should add some additional testcases – I try to do this as Part
2 of this patch.
PPPS: Once the patch is in, some audit needs to be done which parts of
those PRs remain
as follow-up work. I think some still existing issues are covered by
José's pending
patches + for those which are now fixed, the testcase might still be
added.
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