[Bug target/109465] New: LoongArch: The expansion of memcpy is slow and bloated for some sizes

[Bug target/109465] New: LoongArch: The expansion of memcpy is slow and bloated for some sizes

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109465

            Bug ID: 109465
           Summary: LoongArch: The expansion of memcpy is slow and bloated
                    for some sizes
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: xry111 at gcc dot gnu.org
  Target Milestone: ---

extern char *a, *b;

void test() { __builtin_memcpy(a, b, 15); }

With -mno-strict-align, this is compiled to 15 ld.bu/st.b pairs instead of the
optimal (4 pairs).

All size values >= 19 (except 24) seem affected.

[Bug target/109465] LoongArch: The expansion of memcpy is slow and bloated for some sizes

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109465

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-04-10
                 CC|                            |chenglulu at loongson dot cn
             Target|                            |loongarch64-linux-gnu
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Not a regression nor "serious" issue, the fix can be deferred into GCC 14 stage
1.

[Bug target/109465] LoongArch: The expansion of memcpy is slow and bloated for some sizes

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109465

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Xi Ruoyao <xry111@gcc.gnu.org>:

https://gcc.gnu.org/g:6d7e0bcfa49e4ddc84dabe520bba8a023bc52692

commit r14-70-g6d7e0bcfa49e4ddc84dabe520bba8a023bc52692
Author: Xi Ruoyao <xry111@xry111.site>
Date:   Wed Apr 12 11:45:48 2023 +0000

    LoongArch: Improve cpymemsi expansion [PR109465]

    We'd been generating really bad block move sequences which is recently
    complained by kernel developers who tried __builtin_memcpy.  To improve
    it:

    1. Take the advantage of -mno-strict-align.  When it is set, set mode
       size to UNITS_PER_WORD regardless of the alignment.
    2. Half the mode size when (block size) % (mode size) != 0, instead of
       falling back to ld.bu/st.b at once.
    3. Limit the length of block move sequence considering the number of
       instructions, not the size of block.  When -mstrict-align is set and
       the block is not aligned, the old size limit for straight-line
       implementation (64 bytes) was definitely too large (we don't have 64
       registers anyway).

    Change since v1: add a comment about the calculation of num_reg.

    gcc/ChangeLog:

            PR target/109465
            * config/loongarch/loongarch-protos.h
            (loongarch_expand_block_move): Add a parameter as alignment RTX.
            * config/loongarch/loongarch.h:
            (LARCH_MAX_MOVE_BYTES_PER_LOOP_ITER): Remove.
            (LARCH_MAX_MOVE_BYTES_STRAIGHT): Remove.
            (LARCH_MAX_MOVE_OPS_PER_LOOP_ITER): Define.
            (LARCH_MAX_MOVE_OPS_STRAIGHT): Define.
            (MOVE_RATIO): Use LARCH_MAX_MOVE_OPS_PER_LOOP_ITER instead of
            LARCH_MAX_MOVE_BYTES_PER_LOOP_ITER.
            * config/loongarch/loongarch.cc (loongarch_expand_block_move):
            Take the alignment from the parameter, but set it to
            UNITS_PER_WORD if !TARGET_STRICT_ALIGN.  Limit the length of
            straight-line implementation with LARCH_MAX_MOVE_OPS_STRAIGHT
            instead of LARCH_MAX_MOVE_BYTES_STRAIGHT.
            (loongarch_block_move_straight): When there are left-over bytes,
            half the mode size instead of falling back to byte mode at once.
            (loongarch_block_move_loop): Limit the length of loop body with
            LARCH_MAX_MOVE_OPS_PER_LOOP_ITER instead of
            LARCH_MAX_MOVE_BYTES_PER_LOOP_ITER.
            * config/loongarch/loongarch.md (cpymemsi): Pass the alignment
            to loongarch_expand_block_move.

    gcc/testsuite/ChangeLog:

            PR target/109465
            * gcc.target/loongarch/pr109465-1.c: New test.
            * gcc.target/loongarch/pr109465-2.c: New test.
            * gcc.target/loongarch/pr109465-3.c: New test.

[Bug target/109465] LoongArch: The expansion of memcpy is slow and bloated for some sizes

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109465

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Fixed for GCC 14.  Not suitable for backporting.

[Bug target/109465] LoongArch: The expansion of memcpy is slow and bloated for some sizes

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109465

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |14.0