On Wed, 12 Jun 2024, Patrick Palka wrote:
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/14?
>
> -- >8 --
>
> Here during overload resolution we have two strictly viable ambiguous
> candidates #1 and #2, and two non-strictly viable candidates #3 and #4
> which we hold on to ever since r14-6522. These latter candidates have
> an empty third arg conversion since the second arg conversion was deemed
> bad. This ends up causing an ICE during joust for #3 and #4 due to this
> empty arg conversion.
>
> We can fix this by making joust robust to empty arg conversions, but in
> this situation we shouldn't need to compare #3 and #4 at all given that
> we have a strictly viable candidate. To that end, this patch makes
> tourney shortcut considering non-strictly viable candidates upon
> encountering ambiguity between two strictly viable candidates, taking
> advantage of the fact that the candidates list is sorted according to
> viability via splice_viable.
>
> PR c++/115239
>
> gcc/cp/ChangeLog:
>
> * call.cc (tourney): Don't consider a non-strictly viable
> candidate as the champ if there was ambiguity between two
> strictly viable candidates.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/overload/error7.C: New test.
> ---
> gcc/cp/call.cc | 4 +++-
> gcc/testsuite/g++.dg/overload/error7.C | 10 ++++++++++
> 2 files changed, 13 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/overload/error7.C
>
> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
> index ed68eb3c568..82c70f5c39f 100644
> --- a/gcc/cp/call.cc
> +++ b/gcc/cp/call.cc
> @@ -13484,9 +13484,11 @@ tourney (struct z_candidate *candidates,
> tsubst_flags_t complain)
> }
> else
> {
> + z_candidate *prev_champ = *champ;
> previous_worse_champ = nullptr;
> champ = &(*challenger)->next;
> - if (!*champ || !(*champ)->viable)
> + if (!*champ || !(*champ)->viable
> + || (prev_champ->viable == 1 && (*champ)->viable == -1))
> {
> champ = nullptr;
> break;
> diff --git a/gcc/testsuite/g++.dg/overload/error7.C
> b/gcc/testsuite/g++.dg/overload/error7.C
> new file mode 100644
> index 00000000000..68aaa236de4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/overload/error7.C
> @@ -0,0 +1,10 @@
> +// PR c++/115239
> +
> +bool foo(const char *, char *, long); // #1, strictly viable, ambig with
> #2
> +bool foo(const char *, char *, unsigned); // #2, strictly viable, ambig with
> #1
> +bool foo(char, char, long); // #3, non-strictly viable
> +bool foo(char, char, unsigned); // #4, non-strictly viable
> +
> +int main() {
> + foo((char *)0, (char *)0, 0); // { dg-error "ambiguous" }
> +}
FWIW I just realized this testcase can be simplified to:
// PR c++/115239
bool foo(char *, long); // #1, strictly viable, ambig with #2
bool foo(char *, unsigned); // #2, strictly viable, ambig with #1
bool foo(char, long); // #3, non-strictly viable
bool foo(char, unsigned); // #4, non-strictly viable
int main() {
foo((char *)0, 0); // { dg-error "ambiguous" }
}
