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Subject: [Bug target/102125] (ARM Cortex-M3 and newer) missed optimization.
 memcpy not needed operations
Date: Mon, 13 Sep 2021 10:27:23 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102125

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Earnshaw <rearnsha@gcc.gnu.or=
g>:

https://gcc.gnu.org/g:5f6a6c91d7c592cb49f7c519f289777eac09bb74

commit r12-3482-g5f6a6c91d7c592cb49f7c519f289777eac09bb74
Author: Richard Earnshaw <rearnsha@arm.com>
Date:   Fri Sep 3 17:06:15 2021 +0100

    gimple: allow more folding of memcpy [PR102125]

    The current restriction on folding memcpy to a single element of size
    MOVE_MAX is excessively cautious on most machines and limits some
    significant further optimizations.  So relax the restriction provided
    the copy size does not exceed MOVE_MAX * MOVE_RATIO and that a SET
    insn exists for moving the value into machine registers.

    Note that there were already checks in place for having misaligned
    move operations when one or more of the operands were unaligned.

    On Arm this now permits optimizing

    uint64_t bar64(const uint8_t *rData1)
    {
        uint64_t buffer;
        memcpy(&buffer, rData1, sizeof(buffer));
        return buffer;
    }

    from
            ldr     r2, [r0]        @ unaligned
            sub     sp, sp, #8
            ldr     r3, [r0, #4]    @ unaligned
            strd    r2, [sp]
            ldrd    r0, [sp]
            add     sp, sp, #8

    to
            mov     r3, r0
            ldr     r0, [r0]        @ unaligned
            ldr     r1, [r3, #4]    @ unaligned

    PR target/102125 - (ARM Cortex-M3 and newer) missed optimization. memcpy
not needed operations

    gcc/ChangeLog:

            PR target/102125
            * gimple-fold.c (gimple_fold_builtin_memory_op): Allow folding
            memcpy if the size is not more than MOVE_MAX * MOVE_RATIO.=