Dear Gilles, > -----Ursprüngliche Nachricht----- > Von: Gilles Gouaillardet <gil...@rist.or.jp> > Gesendet: Freitag, 12. April 2019 02:25 > An: Bader, Reinhold <reinhold.ba...@lrz.de>; Paul Richard Thomas > <paul.richard.tho...@gmail.com>; fort...@gcc.gnu.org; gcc-patches <gcc- > patc...@gcc.gnu.org> > Betreff: Re: AW: [Patch, fortran] PRs 89843 and 90022 - C Fortran Interop > fixes. > > Reinhold, > > > Thanks for the insights ! > > > That means there is currently an other issue since copy-in is performed even > if the argument is declared as ASYNCHRONOUS. > > > I gave the copy-in mechanism some more thoughts, and as a library > developers, I can clearly see a need *not* to do that > > on a case-by-case basis, mainly for performance reasons, but also to be > friendly with legacy apps that are not strictly standard compliant. > > At this stage, I think the best way to move forward is to add an other > directive in the interface definition. > > > for example, we could declare > > > module foo > > interface > > subroutine bar_f08(buf) BIND(C, name="bar_c") > > implicit none > > !GCC$ ATTRIBUTES NO_COPY_IN :: buf
maybe so, but some care must be taken to perform proper checking in case copy-in is necessary - these situations exist as well. For example, if the declaration for buf is TYPE(*), DIMENSION(..), INTENT(IN), CONTIGUOUS :: buf and the actual argument is a discontiguous array section. My preference is for the compiler to automatically avoid copy-in whenever possible. Cheers Reinhold > > TYPE(*), DIMENSION(..), INTENT(IN) :: buf > > end subroutine > > end interface > > end module > > > Does this make sense ? > > > Gilles > > On 4/10/2019 4:22 PM, Bader, Reinhold wrote: > > Hi Gilles, > > > >> I also found an other potential issue with copy-in. > >> > >> If in Fortran, we > >> > >> call foo(buf(0,0)) > >> > >> then the C subroutine can only access buf(0,0), and other elements such > >> as buf(1025,1025) cannot be accessed. > >> > >> Such elements are valid in buf, but out of bounds in the copy (that > >> contains a single element). > >> > >> Strictly speaking, I cannot say whether this is a violation of the > >> standard or not, but I can see how this will > >> > >> break a lot of existing apps (once again, those apps might be incorrect > >> in the first place, but most of us got used to them working). > > > > The above call will only be conforming if the dummy argument is declared > > assumed or explicit size. > > Otherwise, the compiler should reject it due to rank mismatch. For > assumed > > rank, the call would be > > legitimate, but the rank of the dummy argument is then zero. Even if no > > copy-in is performed, > > accessing data beyond the address range of that scalar is not strictly > > allowed. > > > > Of more interest is the situation where the dummy argument in Fortran is > > declared, e.g., > > > > TYPE(*), ASYNCHRONOUS, INTENT(IN) :: BUF(..) > > > > The standard's semantics *forbids* performing copy-in/out in this case, > IIRC. > > Otherwise > > ASYNCHRONOUS semantics would not work, and non-blocking MPI calls > would fail > > due > > to buffers vanishing into thin air. > > > > Regards > > Reinhold > > > >> To me, this is a second reason why copy-in is not desirable (at least as > >> a default option). > >> > >> > >> > >> Cheers, > >> > >> > >> Gilles > >> > >> On 4/9/2019 7:18 PM, Paul Richard Thomas wrote: > >>> The most part of this patch is concerned with implementing calls from > >>> C of of fortran bind c procedures with assumed shape or assumed rank > >>> dummies to completely fix PR89843. The conversion of the descriptors > >>> from CFI to gfc occur on entry to and reversed on exit from the > >>> procedure. > >>> > >>> This patch is safe for trunk, even at this late stage, because its > >>> effects are barricaded behind the tests for CFI descriptors. I believe > >>> that it appropriately rewards the bug reporters to have this feature > >>> work as well as possible at release. > >>> > >>> Between comments and the ChangeLogs, this patch is self explanatory. > >>> > >>> Bootstrapped and regtested on FC29/x86_64 - OK for trunk? > >>> > >>> Paul > >>> > >>> 2019-04-09 Paul Thomas <pa...@gcc.gnu.org> > >>> > >>> PR fortran/89843 > >>> * trans-decl.c (gfc_get_symbol_decl): Assumed shape and assumed > >>> rank dummies of bind C procs require deferred initialization. > >>> (convert_CFI_desc): New procedure to convert incoming CFI > >>> descriptors to gfc types and back again. > >>> (gfc_trans_deferred_vars): Call it. > >>> * trans-expr.c (gfc_conv_gfc_desc_to_cfi_desc): Null the CFI > >>> descriptor pointer. Free the descriptor in all cases. > >>> > >>> PR fortran/90022 > >>> * trans-decl.c (gfc_get_symbol_decl): Make sure that the se > >>> expression is a pointer type before converting it to the symbol > >>> backend_decl type. > >>> > >>> 2019-04-09 Paul Thomas <pa...@gcc.gnu.org> > >>> > >>> PR fortran/89843 > >>> * gfortran.dg/ISO_Fortran_binding_4.f90: Modify the value of x > >>> in ctg. Test the conversion of the descriptor types in the main > >>> program. > >>> * gfortran.dg/ISO_Fortran_binding_10.f90: New test. > >>> * gfortran.dg/ISO_Fortran_binding_10.c: Called by it. > >>> > >>> PR fortran/90022 > >>> * gfortran.dg/ISO_Fortran_binding_1.c: Correct the indexing for > >>> the computation of 'ans'. Also, change the expected results for > >>> CFI_is_contiguous to comply with standard. > >>> * gfortran.dg/ISO_Fortran_binding_1.f90: Correct the expected > >>> results for CFI_is_contiguous to comply with standard. > >>> * gfortran.dg/ISO_Fortran_binding_9.f90: New test. > >>> * gfortran.dg/ISO_Fortran_binding_9.c: Called by it. > >>> > >>> 2019-04-09 Paul Thomas <pa...@gcc.gnu.org> > >>> > >>> PR fortran/89843 > >>> * runtime/ISO_Fortran_binding.c (cfi_desc_to_gfc_desc): Only > >>> return immediately if the source pointer is null. Bring > >>> forward the extraction of the gfc type. Extract the kind so > >>> that the element size can be correctly computed for sections > >>> and components of derived type arrays. Remove the free of the > >>> CFI descriptor since this is now done in trans-expr.c. > >>> (gfc_desc_to_cfi_desc): Only allocate the CFI descriptor if it > >>> is not null. > >>> (CFI_section): Normalise the difference between the upper and > >>> lower bounds by the stride to correctly calculate the extents > >>> of the section. > >>> > >>> PR fortran/90022 > >>> * runtime/ISO_Fortran_binding.c (CFI_is_contiguous) : Return > >>> 1 for true and 0 otherwise to comply with the standard. Correct > >>> the contiguity check for rank 3 and greater by using the stride > >>> measure of the lower dimension rather than the element length.
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