On Sun, Jun 29, 2025, 4:36 PM Antoni Boucher <boua...@zoho.com> wrote:
> > > 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". > Not all ABI/targets have a sret specific register. So this is even more confusing. > > > > 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. > Yes it is guaranteed that if the return type is returned via memory reference to the other function it will use that memory location. Even for things like a->b = func(...)[RSO]. It is even used by the c++ frontend that way. > > > > > > > > Is that what you are looking for? > > > > > > Thanks, > > Andrew > > > > Thanks. > > > >
