Re: Manually set sret parameter

[Antoni Boucher via Gcc]

Le 2025-06-29 à 10 h 46, Andrew Pinski a écrit :


On Sun, Jun 29, 2025, 7:43 AM Andrew Pinski <pins...@gmail.com 
<mailto:pins...@gmail.com>> wrote:

    On Sun, Jun 29, 2025, 7:36 AM Antoni Boucher via Gcc
    <gcc@gcc.gnu.org <mailto:gcc@gcc.gnu.org>> wrote:

        Hi.
        Is there a way in GENERIC to specify that a parameter will be
        passed in
        "sret", or is this solely controlled by the hook struct_value_rtx?


    It is only controlled by the hook.
    What exactly are trying to do?
    You could set the return slot optimization bit on the call
    expression if you want the lhs of a call not to be copied and just
    passed as the address via sret.

I'm trying to follow the Rust ABI for rustc_codegen_gcc: they manually 
specify whether a param is "sret".


    That is if you have:
    StructVar = func(...);

    You set the return slot optimization bit on the call expr in generic
    and which will copy that bit to the gimple GIMPLE_CALL and then
    during expand will again copy it back to the generic call_expr and
    expand will use the target for the address.


CALL_EXPR_RETURN_SLOT_OPT is the macro.

Is this a guaranteed optimization? I'm asking because this is for ABI 
correctness and I need a solution that will always work.
If not, would there be another way to do this?
Thanks.




    Is that what you are looking for?


    Thanks,
    Andrew

        Thanks.