On Wed, 12 Jun 2024, Jason Merrill wrote:
> On 6/12/24 13:56, 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))
>
> Maybe
>
> (!*champ || (*champ)->viable < prev_champ->viable) ?
>
> OK with that change.
Nice, done. In passing it occurred to me that we can just consider
challenger->viable instead of prev_champ->viable (they must be the
same since there was ambiguity), so we don't need to introduce
prev_champ.
This is what I ended up pushing:
-- >8 --
Subject: [PATCH] c++: ICE w/ ambig and non-strictly-viable cands [PR115239]
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.
Reviewed-by: Jason Merrill <ja...@redhat.com>
---
gcc/cp/call.cc | 3 ++-
gcc/testsuite/g++.dg/overload/error7.C | 10 ++++++++++
2 files changed, 12 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 85536fc25ff..7bbc1fb0c78 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -13490,7 +13490,8 @@ tourney (struct z_candidate *candidates, tsubst_flags_t
complain)
{
previous_worse_champ = nullptr;
champ = &(*challenger)->next;
- if (!*champ || !(*champ)->viable)
+ if (!*champ || !(*champ)->viable
+ || (*champ)->viable < (*challenger)->viable)
{
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..de50ce5f66e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/overload/error7.C
@@ -0,0 +1,10 @@
+// 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" }
+}
--
2.45.2.457.g8d94cfb545
