On Mon, Sep 6, 2021 at 12:40 PM Richard Earnshaw <rearn...@arm.com> wrote:
>
>
> 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
OK.
Thanks,
Richard.
> 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.
> ---
> gcc/gimple-fold.c | 16 +++++++++++-----
> 1 file changed, 11 insertions(+), 5 deletions(-)
>
