[Bug tree-optimization/97053] [10/11 Regression] an O2, O3 codegen bug

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97053

--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-9 branch has been updated by Jakub Jelinek
<jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:a24744c1ed89e255f3db5b3981519f538d231886

commit r9-8918-ga24744c1ed89e255f3db5b3981519f538d231886
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Sep 16 09:42:33 2020 +0200

    store-merging: Consider also overlapping stores earlier in the by bitpos
sorting [PR97053]

    As the testcases show, if we have something like:
      MEM <char[12]> [&b + 8B] = {};
      MEM[(short *) &b] = 5;
      _5 = *x_4(D);
      MEM <long long unsigned int> [&b + 2B] = _5;
      MEM[(char *)&b + 16B] = 88;
      MEM[(int *)&b + 20B] = 1;
    then in sort_by_bitpos the stores are almost like in the given order,
    except the first store is after the = _5; store.
    We can't coalesce the = 5; store with = _5;, because the latter is MEM_REF,
    while the former INTEGER_CST, and we can't coalesce the = _5 store with
    the = {} store because the former is MEM_REF, the latter INTEGER_CST.
    But we happily coalesce the remaining 3 stores, which is wrong, because the
    = _5; store overlaps those and is in between them in the program order.
    We already have code to deal with similar cases in check_no_overlap, but we
    deal only with the following stores in sort_by_bitpos order, not the
earlier
    ones.

    The following patch checks also the earlier ones.  In
coalesce_immediate_stores
    it computes the first one that needs to be checked (all the ones whose
    bitpos + bitsize is smaller or equal to merged_store->start don't need to
be
    checked and don't need to be checked even for any following attempts
because
    of the sort_by_bitpos sorting) and the end of that (that is the first store
    in the merged_store).

    2020-09-16  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/97053
            * gimple-ssa-store-merging.c (check_no_overlap): Add FIRST_ORDER,
            START, FIRST_EARLIER and LAST_EARLIER arguments.  Return false if
            any stores between FIRST_EARLIER inclusive and LAST_EARLIER
exclusive
            has order in between FIRST_ORDER and LAST_ORDER and overlaps the to
            be merged store.
            (imm_store_chain_info::try_coalesce_bswap): Add FIRST_EARLIER
argument.
            Adjust check_no_overlap caller.
            (imm_store_chain_info::coalesce_immediate_stores): Add
first_earlier
            and last_earlier variables, adjust them during iterations.  Adjust
            check_no_overlap callers, call check_no_overlap even when extending
            overlapping stores by extra INTEGER_CST stores.

            * gcc.dg/store_merging_31.c: New test.
            * gcc.dg/store_merging_32.c: New test.

    (cherry picked from commit bd909071ac04e94f4b6f0baab64d0687ec55681d)