From 1c522c9eafa5b86b78cd7b3044e120762fb4c879 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Wed, 3 Jan 2024 15:43:28 -0500
Subject: [PATCH] c++: bad direct reference binding via conv fn [PR113064]
When computing a direct reference binding via a conversion function
yields a bad conversion, reference_binding incorrectly commits to that
conversion instead of trying a conversion via a temporary. This causes
us to reject the first testcase because the bad direct conversion to B&&
via the && conversion operator prevents us from considering the good
conversion via the & conversion operator and a temporary. (Similar
story for the second testcase.)
This patch fixes this by making reference_binding not prematurely commit
to such a bad direct conversion. We still fall back to it if using a
temporary also fails (otherwise the diagnostic for cpp0x/explicit7.C
regresses).
PR c++/113064
gcc/cp/ChangeLog:
* call.cc (reference_binding): Still try a conversion via a
temporary if a direct conversion was bad.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/rv-conv4.C: New test.
* g++.dg/cpp0x/rv-conv5.C: New test.
---
gcc/cp/call.cc | 22 ++++++++++++++++++----
gcc/testsuite/g++.dg/cpp0x/rv-conv4.C | 16 ++++++++++++++++
gcc/testsuite/g++.dg/cpp0x/rv-conv5.C | 23 +++++++++++++++++++++++
3 files changed, 57 insertions(+), 4 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/rv-conv4.C
create mode 100644 gcc/testsuite/g++.dg/cpp0x/rv-conv5.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index d9ddd36cec0d..1c675726f8ca 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -1739,6 +1739,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags,
tsubst_flags_t complain)
{
conversion *conv = NULL;
+ conversion *bad_direct_conv = nullptr;
tree to = TREE_TYPE (rto);
tree from = rfrom;
tree tfrom;
@@ -1925,13 +1926,23 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags,
z_candidate *cand = build_user_type_conversion_1 (rto, expr, flags,
complain);
if (cand)
- return cand->second_conv;
+ {
+ if (!cand->second_conv->bad_p)
+ return cand->second_conv;
+
+ /* Direct reference binding wasn't successful and yielded a bad
+ conversion. Proceed with trying to go through a temporary
+ instead, and if that also fails then we'll return this bad
+ conversion rather than no conversion for sake of better
+ diagnostics. */
+ bad_direct_conv = cand->second_conv;
+ }
}
/* From this point on, we conceptually need temporaries, even if we
elide them. Only the cases above are "direct bindings". */
if (flags & LOOKUP_NO_TEMP_BIND)
- return NULL;
+ return bad_direct_conv ? bad_direct_conv : nullptr;
/* [over.ics.rank]
@@ -1972,6 +1983,9 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags,
there's no strictly viable candidate. */
if (!maybe_valid_p && (flags & LOOKUP_SHORTCUT_BAD_CONVS))
{
+ if (bad_direct_conv)
+ return bad_direct_conv;
+
conv = alloc_conversion (ck_deferred_bad);
conv->bad_p = true;
return conv;
@@ -1995,7 +2009,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags,
conv = implicit_conversion (to, from, expr, c_cast_p,
flags, complain);
if (!conv)
- return NULL;
+ return bad_direct_conv ? bad_direct_conv : nullptr;
if (conv->user_conv_p)
{
@@ -2018,7 +2032,7 @@ reference_binding (tree rto, tree rfrom, tree expr, bool c_cast_p, int flags,
= reference_binding (rto, ftype, NULL_TREE, c_cast_p,
sflags, complain);
if (!new_second)
- return NULL;
+ return bad_direct_conv ? bad_direct_conv : nullptr;
conv = merge_conversion_sequences (t, new_second);
gcc_assert (maybe_valid_p || conv->bad_p);
return conv;
diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C
new file mode 100644
index 000000000000..7ecd2dc3ccdc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv4.C
@@ -0,0 +1,16 @@
+// PR c++/113064
+// { dg-do compile { target c++11 } }
+
+struct B { };
+
+struct A {
+ operator B() &;
+ operator B&&() &&;
+};
+
+void f(B&&);
+
+int main() {
+ A a;
+ f(a);
+}
diff --git a/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C
new file mode 100644
index 000000000000..dcb6fc6f76f3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/rv-conv5.C
@@ -0,0 +1,23 @@
+// PR c++/113064
+// { dg-do compile { target c++11 } }
+
+struct no_copy {
+ no_copy() = default;
+
+ no_copy(const no_copy&) = delete;
+ no_copy(no_copy&&);
+
+ no_copy& operator=(const no_copy&) = delete;
+ no_copy& operator=(no_copy&&);
+};
+
+struct A {
+ operator no_copy() &;
+ operator no_copy&&() && = delete;
+};
+
+int main() {
+ no_copy nc;
+ A a;
+ nc = a;
+}
--
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