On Fri, 20 Oct 2023, Jason Merrill wrote:
> Tested x86_64-pc-linux-gnu, applying to trunk. Patrick, sorry I didn't apply
> this sooner.
>
> -- 8< --
>
> In r13-3766 I changed the logic at the end of tourney to avoid redundant
> comparisons, but the change also meant skipping any less-good matches
> between the champ_compared_to_predecessor candidate and champ itself.
>
> This should not be a correctness issue, since we believe that joust is a
> partial order. But it can lead to missed warnings, as in this testcase.
I suppose this rules out optimizing tourney via transitivity when in
a non-SFINAE context since it'd cause missed warnings such as these.
But maybe we'd still want to optimize the second pass via transitivity
in a SFINAE context?
>
> gcc/cp/ChangeLog:
>
> * call.cc (tourney): Only skip champ_compared_to_predecessor.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/warn/Wsign-promo1.C: New test.
> ---
> gcc/cp/call.cc | 5 +++--
> gcc/testsuite/g++.dg/warn/Wsign-promo1.C | 15 +++++++++++++++
> 2 files changed, 18 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/warn/Wsign-promo1.C
>
> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
> index 657eca93d23..a49fde949d5 100644
> --- a/gcc/cp/call.cc
> +++ b/gcc/cp/call.cc
> @@ -13227,10 +13227,11 @@ tourney (struct z_candidate *candidates,
> tsubst_flags_t complain)
> been compared to. */
>
> for (challenger = candidates;
> - challenger != champ
> - && challenger != champ_compared_to_predecessor;
> + challenger != champ;
> challenger = challenger->next)
> {
> + if (challenger == champ_compared_to_predecessor)
> + continue;
> fate = joust (champ, challenger, 0, complain);
> if (fate != 1)
> return NULL;
> diff --git a/gcc/testsuite/g++.dg/warn/Wsign-promo1.C
> b/gcc/testsuite/g++.dg/warn/Wsign-promo1.C
> new file mode 100644
> index 00000000000..51b76eee735
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wsign-promo1.C
> @@ -0,0 +1,15 @@
> +// Check that we get joust warnings from comparing the final champ to a
> +// candidate between it and the previous champ.
> +
> +// { dg-additional-options -Wsign-promo }
> +
> +struct A { A(int); };
> +
> +enum E { e };
> +
> +int f(int, A);
> +int f(unsigned, A);
> +int f(int, int);
> +
> +int i = f(e, 42); // { dg-warning "passing 'E'" }
> +// { dg-warning "in call to 'int f" "" { target *-*-* } .-1 }
>
> base-commit: 084addf8a700fab9222d4127ab8524920d0ca481
> --
> 2.39.3
>
>
