On 8/1/24 4:19 PM, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
This fixes another false positive. When a function is taking a
temporary of scalar type that couldn't be bound to the return type
of the function, don't warn, such a program would be ill-formed.
Thanks to Jonathan for reporting the problem.
PR c++/115987
gcc/cp/ChangeLog:
* call.cc (do_warn_dangling_reference): Don't consider a
temporary with a scalar type that cannot bind to the return type.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wdangling-reference22.C: New test.
---
gcc/cp/call.cc | 15 +++++++++++++--
.../g++.dg/warn/Wdangling-reference22.C | 19 +++++++++++++++++++
2 files changed, 32 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wdangling-reference22.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 40cb582acc7..375256ebcc4 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -14290,8 +14290,19 @@ do_warn_dangling_reference (tree expr, bool arg_p)
/* Recurse to see if the argument is a temporary. It could also
be another call taking a temporary and returning it and
initializing this reference parameter. */
- if (do_warn_dangling_reference (arg, /*arg_p=*/true))
- return expr;
+ if ((arg = do_warn_dangling_reference (arg, /*arg_p=*/true)))
+ {
+ /* If we know the temporary could not bind to the return type,
+ don't warn. This is for scalars only because for classes
+ we can't be sure we are not returning its sub-object. */
+ if (SCALAR_TYPE_P (TREE_TYPE (arg))
+ && TYPE_REF_P (rettype)
+ && SCALAR_TYPE_P (TREE_TYPE (rettype))
I don't think we need to check for scalar return type, only argument type.
+ && !reference_related_p (TREE_TYPE (arg),
+ TREE_TYPE (rettype)))
+ continue;
+ return expr;
+ }
/* Don't warn about member functions like:
std::any a(...);
S& s = a.emplace<S>({0}, 0);
diff --git a/gcc/testsuite/g++.dg/warn/Wdangling-reference22.C
b/gcc/testsuite/g++.dg/warn/Wdangling-reference22.C
new file mode 100644
index 00000000000..0381f9313fb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wdangling-reference22.C
@@ -0,0 +1,19 @@
+// PR c++/115987
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wdangling-reference" }
+
+template <typename T>
+struct Wrapper {
+ T val;
+};
+
+template <typename T, typename FUNC>
+ const T& unwrap_2(const Wrapper<T>& r, FUNC&&) {
+ return r.val;
+}
+
+int main(int, char**) {
+ const Wrapper<int> w{1234};
+ const auto& u = unwrap_2(w, 1L); // { dg-bogus "dangling reference" }
+ __builtin_printf("Unwrapped value : %d\n", u);
+}
base-commit: 1f53319cae81aea438b6c0ba55f49e5669acf1c8
