Am Freitag, den 04.10.2019, 12:29 +0200 schrieb Richard Biener:
> On Wed, Oct 2, 2019 at 8:24 PM Uecker, Martin
> <[email protected]> wrote:
> >
> > Am Mittwoch, den 02.10.2019, 17:37 +0200 schrieb Richard Biener:
> >
> > ...
> >
> > > > > Oh, and LTO does _not_ merge types declared inside a function,
> > > > > so
> > > > >
> > > > > void foo () { struct S { int i; }; }
> > > > > void bar () { struct S { int i; }; }
> > > > >
> > > > > the two S are distinct and objects of that type do not conflict.
> > > >
> > > > This is surprising as these types are compatible across TUs. So
> > > > if some pointer is passed between these functions this is
> > > > supposed to work.
> > >
> > > So if they are compatible the frontend needs to mark them so in this case.
> >
> > It can't. The front end never sees the other TU.
>
> If the type "leaves" the CU via a call the called function has a prototype
> through which it "sees" the CU.
The prototype could be local to the function or it could be a void*
(or other pointer type) argument.
TU1-----------------------
#include <stdio.h>
extern void f(void *p);
int main()
{
struct foo { int x; } b;
b.x = 2;
f(&b);
printf("%d\n", b.x);
}
TU2-----------------------------
extern void f(void *p)
{
struct foo { int x; } *q = p;
q->x = 3;
}
Best,
Martin
