[Bug debug/105089] CTF for a defined extern variable is ambiguous

["cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105089

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Indu Bhagat <ibhagat@gcc.gnu.org>:

https://gcc.gnu.org/g:d0b00e74bf59c73b79471bbe9de19373b8661e20

commit r12-8163-gd0b00e74bf59c73b79471bbe9de19373b8661e20
Author: Indu Bhagat <indu.bhagat@oracle.com>
Date:   Thu Apr 14 10:01:22 2022 -0700

    CTF for extern variable fix [PR105089]

    The CTF format cannot differentiate between a non-defining extern
    variable declaration vs. a defining variable declaration (unlike DWARF).
    So, the correct behaviour wrt the compiler generating CTF for such
    extern variables (i.e., when both the defining and non-defining decl
    are present in the same CU) is to simply emit the CTF variable
    correspoding to the defining declaration.

    To carry out the above, following changes are introduced via the patch:

    1. The CTF container (ctfc.h) now keeps track of the non-defining
declarations
    (by noting the DWARF attribute DW_AT_specification) in a new
ctfc_ignore_vars
    hashtable.  Such book-keeping is necessary because the CTF container should
    not rely on the order of DWARF DIEs presented to it at generation time.

    2. At the time of ctf_add_variable (), the DW_AT_specification DIE if
present
    is added in the ctfc_ignore_vars hashtable.  The CTF variable generation
for
    the defining declaration continues as normal.

    3. If the ctf_add_variable () is asked to generate CTF variable for a DIE
    present in the ctfc_ignore_vars, it skips generating CTF for it.

    4. Recall that CTF variables are pre-processed before emission.  Till now,
the
    only pre-processing that was being done was to sort them in order of their
    names.  Now an additional step is added:  If the CTF variable which
    corresponds to the non-defining declaration is indeed present in the
ctfc_vars
    hashtable (because the corresponding DWARF DIE was encountered first by the
    CTF generation engine), skip that CTF variable from output.

    An important side effect of such a workflow above is that CTF for the C
type
    of the non-defining decl will remain in the CTF dictionary (and will be
    emitted in the output section as well).  This type can be pruned by the
    link-time de-duplicator as usual, if deemed unused.

    2022-04-14  Indu Bhagat  <indu.bhagat@oracle.com>

    gcc/ChangeLog:

            PR debug/105089
            * ctfc.cc (ctf_dvd_ignore_insert): New function.
            (ctf_dvd_ignore_lookup): Likewise.
            (ctf_add_variable): Keep track of non-defining decl DIEs.
            (new_ctf_container): Initialize the new hash-table.
            (ctfc_delete_container): Empty hash-table.
            * ctfc.h (struct ctf_container): Add new hash-table.
            (ctf_dvd_ignore_lookup): New declaration.
            (ctf_add_variable): Add additional argument.
            * ctfout.cc (ctf_dvd_preprocess_cb): Skip adding CTF variable
            record for non-defining decl for which a defining decl exists
            in the same TU.
            (ctf_preprocess): Defer updating the number of global objts
            until here.
            (output_ctf_header): Use ctfc_vars_list_count as some CTF
            variables may not make it to the final output.
            (output_ctf_vars): Likewise.
            * dwarf2ctf.cc (gen_ctf_variable): Skip generating CTF variable
            if this is known to be a non-defining decl DIE.