[Bug rtl-optimization/114674] [aarch64] ldp_fusion fails to merge 2 strs due to imprecise alignment info

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114674

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Alex Coplan <acoplan@gcc.gnu.org>:

https://gcc.gnu.org/g:74690ff96b263b8609639b7fbc5d6afd3f19cb98

commit r15-282-g74690ff96b263b8609639b7fbc5d6afd3f19cb98
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Wed Apr 10 16:30:36 2024 +0100

    aarch64: Preserve mem info on change of base for ldp/stp [PR114674]

    The ldp/stp fusion pass can change the base of an access so that the two
    accesses end up using a common base register.  So far we have been using
    adjust_address_nv to do this, but this means that we don't preserve
    other properties of the mem we're replacing.  It seems better to use
    replace_equiv_address_nv, as this will preserve e.g. the MEM_ALIGN of the
    mem whose address we're changing.

    The PR shows that by adjusting the other mem we lose alignment
    information about the original access and therefore end up rejecting an
    otherwise viable pair when --param=aarch64-stp-policy=aligned is passed.
    This patch fixes that by using replace_equiv_address_nv instead.

    Notably this is the same approach as taken by
    aarch64_check_consecutive_mems when a change of base is required, so
    this at least makes things more consistent between the ldp fusion pass
    and the peepholes.

    gcc/ChangeLog:

            PR target/114674
            * config/aarch64/aarch64-ldp-fusion.cc (ldp_bb_info::fuse_pair):
            Use replace_equiv_address_nv on a change of base instead of
            adjust_address_nv on the other access.

    gcc/testsuite/ChangeLog:

            PR target/114674
            * gcc.target/aarch64/pr114674.c: New test.