On Mon, Sep 26, 2022 at 11:51:30AM -0400, Patrick Palka wrote:
> On Mon, 26 Sep 2022, Marek Polacek via Gcc-patches wrote:
>
> > Jon reported that evaluating __is_convertible in this test leads to
> > instantiating char_traits<char>::eq, which is invalid (because we
> > are trying to call a member function on a char) and so we fail to
> > compile the test. __is_convertible doesn't and shouldn't need to
> > instantiate so much, so let's limit it with a cp_unevaluated guard.
> >
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > PR c++/106784
> >
> > gcc/cp/ChangeLog:
> >
> > * method.cc (is_convertible): Use cp_unevaluated.
>
> I think is_nothrow_convertible would need cp_unevaluated too (or maybe we
> should define is_nothrow_convertible in terms of is_convertible).
/facepalm, that's what I get by not using a single implementation for both!
> And the testcase can probably be minimized to something like:
>
> struct A;
> struct B { template<class T> B(const T&) noexcept { T::nonexistent; } };
>
> static_assert(__is_convertible(const A&, B));
> static_assert(__is_nothrow_convertible(const A&, B));
Adjusted, thanks.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
Jon reported that evaluating __is_convertible in a test led to
instantiating something ill-formed and so we failed to compile the test.
__is_convertible doesn't and shouldn't need to instantiate so much, so
let's limit it with a cp_unevaluated guard. Use a helper function to
implement both built-ins.
PR c++/106784
gcc/cp/ChangeLog:
* method.cc (is_convertible_helper): New.
(is_convertible): Use it.
(is_nothrow_convertible): Likewise.
gcc/testsuite/ChangeLog:
* g++.dg/ext/is_convertible3.C: New test.
* g++.dg/ext/is_nothrow_convertible3.C: New test.
---
gcc/cp/method.cc | 23 ++++++++++++-------
gcc/testsuite/g++.dg/ext/is_convertible3.C | 9 ++++++++
.../g++.dg/ext/is_nothrow_convertible3.C | 9 ++++++++
3 files changed, 33 insertions(+), 8 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/ext/is_convertible3.C
create mode 100644 gcc/testsuite/g++.dg/ext/is_nothrow_convertible3.C
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index c35a59fe56c..9f917f13134 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -2236,6 +2236,19 @@ ref_xes_from_temporary (tree to, tree from, bool
direct_init_p)
return ref_conv_binds_directly (to, val, direct_init_p).is_false ();
}
+/* Worker for is_{,nothrow_}convertible. Attempt to perform an implicit
+ conversion from FROM to TO and return the result. */
+
+static tree
+is_convertible_helper (tree from, tree to)
+{
+ if (VOID_TYPE_P (from) && VOID_TYPE_P (to))
+ return integer_one_node;
+ cp_unevaluated u;
+ tree expr = build_stub_object (from);
+ return perform_implicit_conversion (to, expr, tf_none);
+}
+
/* Return true if FROM can be converted to TO using implicit conversions,
or both FROM and TO are possibly cv-qualified void. NB: This doesn't
implement the "Access checks are performed as if from a context unrelated
@@ -2244,10 +2257,7 @@ ref_xes_from_temporary (tree to, tree from, bool
direct_init_p)
bool
is_convertible (tree from, tree to)
{
- if (VOID_TYPE_P (from) && VOID_TYPE_P (to))
- return true;
- tree expr = build_stub_object (from);
- expr = perform_implicit_conversion (to, expr, tf_none);
+ tree expr = is_convertible_helper (from, to);
if (expr == error_mark_node)
return false;
return !!expr;
@@ -2258,10 +2268,7 @@ is_convertible (tree from, tree to)
bool
is_nothrow_convertible (tree from, tree to)
{
- if (VOID_TYPE_P (from) && VOID_TYPE_P (to))
- return true;
- tree expr = build_stub_object (from);
- expr = perform_implicit_conversion (to, expr, tf_none);
+ tree expr = is_convertible_helper (from, to);
if (expr == NULL_TREE || expr == error_mark_node)
return false;
return expr_noexcept_p (expr, tf_none);
diff --git a/gcc/testsuite/g++.dg/ext/is_convertible3.C
b/gcc/testsuite/g++.dg/ext/is_convertible3.C
new file mode 100644
index 00000000000..7a986d075c2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_convertible3.C
@@ -0,0 +1,9 @@
+// PR c++/106784
+// { dg-do compile { target c++11 } }
+// Make sure we don't reject this at runtime by trying to instantiate
+// something that would be ill-formed.
+
+struct A;
+struct B { template<class T> B(const T&) noexcept { T::nonexistent; } };
+
+static_assert(__is_convertible(const A&, B), "");
diff --git a/gcc/testsuite/g++.dg/ext/is_nothrow_convertible3.C
b/gcc/testsuite/g++.dg/ext/is_nothrow_convertible3.C
new file mode 100644
index 00000000000..05b1e1d9ad9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_nothrow_convertible3.C
@@ -0,0 +1,9 @@
+// PR c++/106784
+// { dg-do compile { target c++11 } }
+// Make sure we don't reject this at runtime by trying to instantiate
+// something that would be ill-formed.
+
+struct A;
+struct B { template<class T> B(const T&) noexcept { T::nonexistent; } };
+
+static_assert(__is_nothrow_convertible(const A&, B), "");
base-commit: 099a66498bf7a40764002793eba66c881a251b76
--
2.37.3
