On Tue, 25 Mar 2025, Andi Kleen wrote:
> On Tue, Mar 25, 2025 at 07:43:28PM +0300, Alexander Monakov wrote:
> > Hello,
> >
> > FWIW I think Clang made a mistake in bending semantics in a way that is
> > clearly
> > misaligned with the general design of C and C++, where a language-native,
> > so to
> > speak, solution was available: introduce a scope for the local variables to
> > indicate that they cannot escape to the intended tailcall:
> >
> > void foo(int v)
> > {
> > {
> > int a;
> > capture(&a);
> > }
> > tailcall(v); // this cannot refer to 'a', even though it escaped earlier
> > }
>
> This is not a universal fix? e.g. consider a case like
>
> void foo(int v)
> {
> int a;
> capture(&a);
> if (condition)
> return tailcall(v);
> // do something with a
> }
This can be rewritten as
void foo(int v)
{
{
int a;
capture(&a);
if (condition)
goto tail_position;
// do something with a
}
tail_position:
tailcall(v);
}
or with 'do { ... if (...) break; ...} while (0)' when one prefers that to goto.
Alexander
