[Bug ipa/103083] [10/11/12 Regression] Wrong code due to ipa-cp's bits value propagation since r10-5538-gc7ac9a0c7e3916f1

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103083

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Martin Jambor
<jamborm@gcc.gnu.org>:

https://gcc.gnu.org/g:4f939ac1e295f38624c82fa75fa798e83d825232

commit r11-9775-g4f939ac1e295f38624c82fa75fa798e83d825232
Author: Martin Jambor <mjambor@suse.cz>
Date:   Mon Apr 4 19:31:42 2022 +0200

    ipa: Careful processing ANCESTOR jump functions and NULL pointers (PR
103083)

    IPA_JF_ANCESTOR jump functions are constructed also when the formal
    parameter of the caller is first checked whether it is NULL and left
    as it is if it is NULL, to accommodate C++ casts to an ancestor class.

    The jump function type was invented for devirtualization and IPA-CP
    propagation of tree constants is also careful to apply it only to
    existing DECLs(*) but as PR 103083 shows, the part propagating "known
    bits" was not careful about this, which can lead to miscompilations.

    This patch introduces a flag to the ancestor jump functions which
    tells whether a NULL-check was elided when creating it and makes the
    bits propagation behave accordingly, masking any bits otherwise would
    be known to be one.  This should safely preserve alignment info, which
    is the primary ifnormation that we keep in bits for pointers.

    (*) There still may remain problems when a DECL resides on address
    zero (with -fno-delete-null-pointer-checks ...I hope it cannot happen
    otherwise).  I am looking into that now but I think it will be easier
    for everyone if I do so in a follow-up patch.

    gcc/ChangeLog:

    2022-02-11  Martin Jambor  <mjambor@suse.cz>

            PR ipa/103083
            * ipa-prop.h (ipa_ancestor_jf_data): New flag keep_null;
            (ipa_get_jf_ancestor_keep_null): New function.
            * ipa-prop.c (ipa_set_ancestor_jf): Initialize keep_null field of
the
            ancestor function.
            (compute_complex_assign_jump_func): Pass false to keep_null
            parameter of ipa_set_ancestor_jf.
            (compute_complex_ancestor_jump_func): Pass true to keep_null
            parameter of ipa_set_ancestor_jf.
            (update_jump_functions_after_inlining): Carry over keep_null from
the
            original ancestor jump-function or merge them.
            (ipa_write_jump_function): Stream keep_null flag.
            (ipa_read_jump_function): Likewise.
            (ipa_print_node_jump_functions_for_edge): Print the new flag.
            * ipa-cp.c (class ipcp_bits_lattice): Make various getters const. 
New
            member function known_nonzero_p.
            (ipcp_bits_lattice::known_nonzero_p): New.
            (ipcp_bits_lattice::meet_with_1): New parameter drop_all_ones,
            observe it.
            (ipcp_bits_lattice::meet_with): Likewise.
            (propagate_bits_across_jump_function): Simplify.  Pass true in
            drop_all_ones when it is necessary.
            (propagate_aggs_across_jump_function): Take care of keep_null
            flag.
            (ipa_get_jf_ancestor_result): Propagate NULL accross keep_null
            jump functions.

    gcc/testsuite/ChangeLog:

    2021-11-25  Martin Jambor  <mjambor@suse.cz>

            * gcc.dg/ipa/pr103083-1.c: New test.
            * gcc.dg/ipa/pr103083-2.c: Likewise.

    (cherry picked from commit 7ea3a73c195a79e6740ae594ee1a14c8bf7a938d)