https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97053
--- Comment #13 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The releases/gcc-8 branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:87ae45cdbd7b70a4c92d5137552228ed9ad9e9e7 commit r8-10518-g87ae45cdbd7b70a4c92d5137552228ed9ad9e9e7 Author: Jakub Jelinek <ja...@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 <ja...@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)
