https://gcc.gnu.org/g:18f6bb9899209ccd41c476254d30596606c81dd7
commit r15-6909-g18f6bb9899209ccd41c476254d30596606c81dd7
Author: Jakub Jelinek <ja...@redhat.com>
Date: Wed Jan 15 08:56:40 2025 +0100
c++: Delete defaulted operator <=> if std::strong_ordering::equal doesn't
convert to its rettype [PR118387]
Note, the PR raises another problem.
If on the same testcase the B b; line is removed, we silently synthetize
operator<=> which will crash at runtime due to returning without a return
statement. That is because the standard says that in that case
it should return static_cast<int>(std::strong_ordering::equal);
but I can't find anywhere wording which would say that if that isn't
valid, the function is deleted.
https://eel.is/c++draft/class.compare#class.spaceship-2.2
seems to talk just about cases where there are some members and their
comparison is invalid it is deleted, but here there are none and it
follows
https://eel.is/c++draft/class.compare#class.spaceship-3.sentence-2
So, we synthetize with tf_none, see the static_cast is invalid, don't
add error_mark_node statement silently, but as the function isn't deleted,
we just silently emit it.
Should the standard be amended to say that the operator should be deleted
even if it has no elements and the static cast from
https://eel.is/c++draft/class.compare#class.spaceship-3.sentence-2
On Fri, Jan 10, 2025 at 12:04:53PM -0500, Jason Merrill wrote:
> That seems pretty obviously what we want, and is what the other compilers
> implement.
This patch implements it then.
2025-01-15 Jakub Jelinek <ja...@redhat.com>
PR c++/118387
* method.cc (build_comparison_op): Set bad if
std::strong_ordering::equal doesn't convert to rettype.
* g++.dg/cpp2a/spaceship-err6.C: Expect another error.
* g++.dg/cpp2a/spaceship-synth17.C: Likewise.
* g++.dg/cpp2a/spaceship-synth-neg6.C: Likewise.
* g++.dg/cpp2a/spaceship-synth-neg7.C: New test.
* testsuite/25_algorithms/default_template_value.cc
(Input::operator<=>): Use auto as return type rather than bool.
Diff:
---
gcc/cp/method.cc | 26 +++++-----
gcc/testsuite/g++.dg/cpp2a/spaceship-err6.C | 2 +-
gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C | 2 +-
gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg7.C | 58 ++++++++++++++++++++++
gcc/testsuite/g++.dg/cpp2a/spaceship-synth17.C | 2 +-
.../25_algorithms/default_template_value.cc | 2 +-
6 files changed, 75 insertions(+), 17 deletions(-)
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 304d11d145c5..3914bbb1ef23 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -1635,6 +1635,18 @@ build_comparison_op (tree fndecl, bool defining,
tsubst_flags_t complain)
rettype = common_comparison_type (comps);
apply_deduced_return_type (fndecl, rettype);
}
+ tree retvaleq;
+ if (code == EQ_EXPR)
+ retvaleq = boolean_true_node;
+ else
+ {
+ tree seql = lookup_comparison_result (cc_strong_ordering,
+ "equal", complain);
+ retvaleq = build_static_cast (input_location, rettype, seql,
+ complain);
+ if (retvaleq == error_mark_node)
+ bad = true;
+ }
if (bad)
{
DECL_DELETED_FN (fndecl) = true;
@@ -1722,19 +1734,7 @@ build_comparison_op (tree fndecl, bool defining,
tsubst_flags_t complain)
}
}
if (defining)
- {
- tree val;
- if (code == EQ_EXPR)
- val = boolean_true_node;
- else
- {
- tree seql = lookup_comparison_result (cc_strong_ordering,
- "equal", complain);
- val = build_static_cast (input_location, rettype, seql,
- complain);
- }
- finish_return_stmt (val);
- }
+ finish_return_stmt (retvaleq);
}
else if (code == NE_EXPR)
{
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-err6.C
b/gcc/testsuite/g++.dg/cpp2a/spaceship-err6.C
index 57fbdb330884..7e36df3ff9f3 100644
--- a/gcc/testsuite/g++.dg/cpp2a/spaceship-err6.C
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-err6.C
@@ -10,7 +10,7 @@ class MyClass
public:
MyClass(int value): mValue(value) {}
- bool operator<=>(const MyClass&) const = default;
+ bool operator<=>(const MyClass&) const = default; // { dg-error "invalid
'static_cast' from type 'const std::strong_ordering' to type 'bool'" }
};
int main()
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C
b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C
index d3f95e13f135..f4df61ed5088 100644
--- a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg6.C
@@ -5,7 +5,7 @@
struct S {
int a; // { dg-error "three-way comparison of 'S::a'
has type 'std::strong_ordering', which does not convert to 'int\\*'" }
- int *operator<=>(const S&) const = default;
+ int *operator<=>(const S&) const = default; // { dg-error "invalid
'static_cast' from type 'const std::strong_ordering' to type 'int\\*'" }
};
bool b = S{} < S{}; // { dg-error "use of deleted function
'constexpr int\\* S::operator<=>\\\(const S&\\\) const'" }
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg7.C
b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg7.C
new file mode 100644
index 000000000000..f3ef9fe13c07
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth-neg7.C
@@ -0,0 +1,58 @@
+// PR c++/118387
+// { dg-do compile { target c++20 } }
+
+#include <compare>
+
+struct A {
+ int operator<=> (const A &) const;
+};
+
+struct B {
+ A a;
+ int operator<=> (const B &) const = default; // { dg-message "'constexpr int
B::operator<=>\\\(const B&\\\) const' is implicitly deleted because the default
definition would be ill-formed:" }
+}; // { dg-error "invalid 'static_cast' from type 'const
std::strong_ordering' to type 'int'" "" { target *-*-* } .-1 }
+
+struct C {
+ int operator<=> (const C &) const = default; // { dg-message "'constexpr int
C::operator<=>\\\(const C&\\\) const' is implicitly deleted because the default
definition would be ill-formed:" }
+}; // { dg-error "invalid 'static_cast' from type 'const
std::strong_ordering' to type 'int'" "" { target *-*-* } .-1 }
+
+struct D {
+ auto operator<=> (const D &) const = default;
+};
+
+struct E {
+ D a; // { dg-error "three-way comparison of 'E::a' has type
'std::strong_ordering', which does not convert to 'int'" }
+ int operator<=> (const E &) const = default; // { dg-message "'constexpr int
E::operator<=>\\\(const E&\\\) const' is implicitly deleted because the default
definition would be ill-formed:" }
+}; // { dg-error "invalid 'static_cast' from type 'const
std::strong_ordering' to type 'int'" "" { target *-*-* } .-1 }
+
+struct F {
+ A a;
+ int operator<=> (const F &) const = default;
+};
+
+struct G {
+ int operator<=> (const G &) const = default;
+};
+
+struct H {
+ D a;
+ int operator<=> (const H &) const = default;
+};
+
+auto
+foo (B a, B b)
+{
+ return a <=> b; // { dg-error "use of deleted function 'constexpr int
B::operator<=>\\\(const B&\\\) const'" }
+}
+
+auto
+bar (C a, C b)
+{
+ return a <=> b; // { dg-error "use of deleted function 'constexpr int
C::operator<=>\\\(const C&\\\) const'" }
+}
+
+auto
+baz (E a, E b)
+{
+ return a <=> b; // { dg-error "use of deleted function 'constexpr int
E::operator<=>\\\(const E&\\\) const'" }
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth17.C
b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth17.C
index a7793314ce1e..050ea330db0d 100644
--- a/gcc/testsuite/g++.dg/cpp2a/spaceship-synth17.C
+++ b/gcc/testsuite/g++.dg/cpp2a/spaceship-synth17.C
@@ -8,7 +8,7 @@ struct B {};
struct A
{
B b; // { dg-error "no match for 'operator<=>' in
'\[^\n\r]*' \\\(operand types are 'B' and 'B'\\\)" }
- int operator<=> (const A &) const = default;
+ int operator<=> (const A &) const = default; // { dg-error "invalid
'static_cast' from type 'const std::strong_ordering' to type 'int'" }
};
int
diff --git a/libstdc++-v3/testsuite/25_algorithms/default_template_value.cc
b/libstdc++-v3/testsuite/25_algorithms/default_template_value.cc
index 3cf51bc087b4..b05234e1f8df 100644
--- a/libstdc++-v3/testsuite/25_algorithms/default_template_value.cc
+++ b/libstdc++-v3/testsuite/25_algorithms/default_template_value.cc
@@ -27,7 +27,7 @@ struct Output
struct Input
{
Input(int, double);
- friend bool operator<=>(const Input &, const Input &) = default;
+ friend auto operator<=>(const Input &, const Input &) = default;
friend Input operator+(const Input &, const Input &);
operator Output() const;
};
