https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71761
Konstantin Kharlamov <Hi-Angel at yandex dot ru> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |Hi-Angel at yandex dot ru
--- Comment #4 from Konstantin Kharlamov <Hi-Angel at yandex dot ru> ---
(In reply to Marc Glisse from comment #3)
> For clang, this seems based on size: up to size 16 they get jmp, starting
> from 17 they get a call.
>
> For gcc, we give up on anything more complicated than a "register":
>
> /* If the LHS of our call is not just a simple register, we can't
> transform this into a tail or sibling call. This situation happens,
> in (e.g.) "*p = foo()" where foo returns a struct. In this case
> we won't have a temporary here, but we need to carry out the side
> effect anyway, so tailcall is impossible.
>
> ??? In some situations (when the struct is returned in memory via
> invisible argument) we could deal with this, e.g. by passing 'p'
> itself as that argument to foo, but it's too early to do this here,
> and expand_call() will not handle it anyway. If it ever can, then
> we need to revisit this here, to allow that situation. */
> if (ass_var && !is_gimple_reg (ass_var))
> return;
>
> The ??? comment is exactly your case.
So this means, if I dump GIMPLE, I should see something wrong, right? When I do
this, given a file named test.cpp and I use `-fdump-tree-all`, the whole GIMPLE
I see in file `test.cpp.231t.optimized` is this:
;; Function g (_Z1gv, funcdef_no=0, decl_uid=2305, cgraph_uid=1,
symbol_order=0)
g ()
{
<bb 2> [local count: 1073741824]:
# DEBUG BEGIN_STMT
<retval> = f (); [return slot optimization] [tail call]
return <retval>;
}
;; Function main (main, funcdef_no=1, decl_uid=2341, cgraph_uid=2,
symbol_order=1) (executed once)
main ()
{
struct token D.2343;
<bb 2> [local count: 1073741824]:
# DEBUG BEGIN_STMT
# DEBUG INLINE_ENTRY g
# DEBUG BEGIN_STMT
D.2343 = f (); [return slot optimization]
D.2343 ={v} {CLOBBER};
return 0;
}
What should I see? Should there be a `goto f` inside `g()` function, or what?
