On Tue, Mar 05, 2024 at 06:19:07PM -0500, Jason Merrill wrote:
> On 3/5/24 17:47, Nathaniel Shead wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk?
> >
> > -- >8 --
> >
> > Unification for conversion operators (DEDUCE_CONV) doesn't perform
> > transformations like handling forwarding references. This is correct in
> > general, but not for xobj parameters, which should be handled "normally"
> > for the purposes of deduction: [temp.deduct.conv] only applies to the
> > return type of the conversion function.
> >
> > PR c++/113629
> >
> > gcc/cp/ChangeLog:
> >
> > * pt.cc (type_unification_real): Use DEDUCE_CALL for xobj
> > parameters of conversion functions.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/cpp23/explicit-obj-conv-op.C: New test.
> >
> > Signed-off-by: Nathaniel Shead <[email protected]>
> > ---
> > gcc/cp/pt.cc | 15 +++++-
> > .../g++.dg/cpp23/explicit-obj-conv-op.C | 49 +++++++++++++++++++
> > 2 files changed, 63 insertions(+), 1 deletion(-)
> > create mode 100644 gcc/testsuite/g++.dg/cpp23/explicit-obj-conv-op.C
> >
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index c4bc54a8fdb..632437d3424 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -23281,6 +23281,10 @@ type_unification_real (tree tparms,
> > in TARGS. */
> > NON_DEFAULT_TEMPLATE_ARGS_COUNT (targs) = NULL_TREE;
> > + bool is_xobj_conv_fn
> > + = (strict == DEDUCE_CONV
> > + && DECL_XOBJ_MEMBER_FUNCTION_P (TREE_TYPE (tparms)));
> > +
> > again:
> > parms = xparms;
> > args = xargs;
> > @@ -23312,10 +23316,17 @@ type_unification_real (tree tparms,
> > parameter pack is a non-deduced context. */
> > continue;
> > + /* For explicit object parameters, unification should behave like
> > + normal function calls, even for conversion functions. This
> > + corresponds to the second (that is, last) argument. */
> > + unification_kind_t kind = strict;
> > + if (is_xobj_conv_fn && ia > 0)
>
> Is it necessary to check the xobj flag? Or can this just be
>
> if (strict == DEDUCE_CONV && ia > 0)
>
> ?
>
> Jason
>
I restricted it to xobj to be conservative, but I think you're right
that it's not necessary: there's nothing special about xobj here apart
from this being a new circumstance where we might actually need to unify
the object parameter.
Here's a new version of the patch. Bootstrapped and regtested (so far
only dg.exp) on x86_64-pc-linux-gnu, OK for trunk if full regtest
completes successfully?
-- >8 --
Unification for conversion operators (DEDUCE_CONV) doesn't perform
transformations like handling forwarding references. This is correct in
general, but not for xobj parameters, which should be handled "normally"
for the purposes of deduction: [temp.deduct.conv] only applies to the
return type of the conversion function.
PR c++/113629
gcc/cp/ChangeLog:
* pt.cc (type_unification_real): Only use DEDUCE_CONV for the
return type of a conversion function.
gcc/testsuite/ChangeLog:
* g++.dg/cpp23/explicit-obj-conv-op.C: New test.
Signed-off-by: Nathaniel Shead <[email protected]>
---
gcc/cp/pt.cc | 12 ++++-
.../g++.dg/cpp23/explicit-obj-conv-op.C | 49 +++++++++++++++++++
2 files changed, 60 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp23/explicit-obj-conv-op.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index c4bc54a8fdb..a6e6c804130 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -23312,10 +23312,18 @@ type_unification_real (tree tparms,
parameter pack is a non-deduced context. */
continue;
+ /* [temp.deduct.conv] only applies to the deduction of the return
+ type, which is always the first argument here. Other arguments
+ (notably, explicit object parameters) should undergo normal
+ call-like unification. */
+ unification_kind_t kind = strict;
+ if (strict == DEDUCE_CONV && ia > 0)
+ kind = DEDUCE_CALL;
+
arg = args[ia];
++ia;
- if (unify_one_argument (tparms, full_targs, parm, arg, subr, strict,
+ if (unify_one_argument (tparms, full_targs, parm, arg, subr, kind,
explain_p))
return 1;
}
@@ -23324,6 +23332,8 @@ type_unification_real (tree tparms,
&& parms != void_list_node
&& TREE_CODE (TREE_VALUE (parms)) == TYPE_PACK_EXPANSION)
{
+ gcc_assert (strict != DEDUCE_CONV);
+
/* Unify the remaining arguments with the pack expansion type. */
tree argvec;
tree parmvec = make_tree_vec (1);
diff --git a/gcc/testsuite/g++.dg/cpp23/explicit-obj-conv-op.C
b/gcc/testsuite/g++.dg/cpp23/explicit-obj-conv-op.C
new file mode 100644
index 00000000000..a6ae4ea1dda
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/explicit-obj-conv-op.C
@@ -0,0 +1,49 @@
+// PR c++/113629
+// { dg-do compile { target c++23 } }
+
+template <typename T> constexpr bool is_lvalue = false;
+template <typename T> constexpr bool is_lvalue<T&> = true;
+
+struct A {
+ constexpr operator bool(this auto&& self) {
+ return is_lvalue<decltype(self)>;
+ }
+};
+
+constexpr A a;
+static_assert(static_cast<bool>(a));
+static_assert((bool)a);
+static_assert(!static_cast<bool>(A{}));
+static_assert(!(bool)A{});
+
+struct B : A {};
+
+constexpr B b;
+static_assert(static_cast<bool>(b));
+static_assert((bool)b);
+static_assert(!static_cast<bool>(B{}));
+static_assert(!(bool)B{});
+
+struct C {
+ template <typename R, typename T>
+ explicit constexpr operator R(this T&&) {
+ return is_lvalue<T>;
+ }
+};
+
+constexpr C c;
+static_assert(static_cast<bool>(c));
+static_assert((bool)c);
+static_assert(!static_cast<bool>(C{}));
+static_assert(!(bool)C{});
+
+struct D {
+ explicit constexpr operator bool(this const D&) { return true; }
+ explicit constexpr operator bool(this const D&&) { return false; }
+};
+
+constexpr D d;
+static_assert(static_cast<bool>(d));
+static_assert((bool)d);
+static_assert(!static_cast<bool>(D{}));
+static_assert(!(bool)D{});
--
2.43.2
