[Bug target/92038] Extremely inefficient x86_64 code for trivally copyable types passed in registers.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92038

--- Comment #9 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Fri Nov  8 10:53:50 2019
New Revision: 277963

URL: https://gcc.gnu.org/viewcvs?rev=277963&root=gcc&view=rev
Log:
        PR target/92038
        * gimple-ssa-store-merging.c (find_constituent_stores): For return
        value only, return non-NULL if there is a single non-clobber
        constituent store even if there are constituent clobbers and return
        one of clobber constituent stores if all constituent stores are
        clobbers.
        (split_group): Handle clobbers.
        (imm_store_chain_info::output_merged_store): When computing
        bzero_first, look after all clobbers at the start.  Don't count
        clobber stmts in orig_num_stmts, except if the first orig store is
        a clobber covering the whole area and split_stores cover the whole
        area, consider equal number of stmts ok.  Punt if split_stores
        contains only ->orig stores and their number plus number of original
        clobbers is equal to original number of stmts.  For ->orig, look past
        clobbers in the constituent stores.
        (imm_store_chain_info::output_merged_stores): Don't remove clobber
        stmts.
        (rhs_valid_for_store_merging_p): Don't return false for clobber stmt
        rhs.
        (store_valid_for_store_merging_p): Allow clobber stmts.
        (verify_clear_bit_region_be): Fix up a thinko in function comment.

        * g++.dg/opt/store-merging-1.C: New test.
        * g++.dg/opt/store-merging-2.C: New test.
        * g++.dg/opt/store-merging-3.C: New test.

Added:
    trunk/gcc/testsuite/g++.dg/opt/store-merging-1.C
    trunk/gcc/testsuite/g++.dg/opt/store-merging-2.C
    trunk/gcc/testsuite/g++.dg/opt/store-merging-3.C
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/gimple-ssa-store-merging.c
    trunk/gcc/testsuite/ChangeLog