Am Freitag, den 04.10.2019, 14:28 +0200 schrieb Richard Biener:
> On Fri, Oct 4, 2019 at 1:55 PM Uecker, Martin
> <martin.uec...@med.uni-goettingen.de> wrote:
> >
> > Am Freitag, den 04.10.2019, 12:29 +0200 schrieb Richard Biener:
> > > On Wed, Oct 2, 2019 at 8:24 PM Uecker, Martin
> > > <martin.uec...@med.uni-goettingen.de> 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;
> > }
>
> If the frontend puts those structures at local scope
> then yes, the above presents a problem to LTO
> at the moment. So, trigger some inlining,
> make main() read b.x after f(&b) and assert that
> it is 3. I think that would fail at the moment.
I expected it to fail, but it seems to work (returns 3).
Maybe by chance.
The example which doesn't work is the one I gave
at the beginning in the thread (even without lto).
Best,
Martin
