warn-access: ignore template parameters when matching operator new/delete [PR109224]

Template parameters on a member operator new cannot affect its member
status nor whether it is a singleton or array operator new, hence, we
can ignore it for purposes of matching.  Similar logic applies to the
placement operator delete.

In the PR (and a lot of idiomatic coroutine code generally), operator
new is templated in order to be able to inspect (some of) the arguments
passed to the coroutine, to make allocation-related decisions.  However,
the coroutine implementation will not call a placement delete form, so
it cannot get templated.  As a result, when demangling, we have an extra
template DEMANGLE_COMPONENT_TEMPLATE around the actual operator new, but
not operator delete.  This terminates new_delete_mismatch_p early.

	PR middle-end/109224 - Wmismatched-new-delete false positive with a templated operator new (common with coroutines)

gcc/ChangeLog:

	PR middle-end/109224
	* gimple-ssa-warn-access.cc (new_delete_mismatch_p): Strip
	DEMANGLE_COMPONENT_TEMPLATE from the operator new and operator
	after demangling.

gcc/testsuite/ChangeLog:

	PR middle-end/109224
	* g++.dg/warn/Wmismatched-new-delete-9.C: New test.

3 files changed, 89 insertions, 1 deletions

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index 820f238..1eb9d2e 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -1765,7 +1765,23 @@ new_delete_mismatch_p (tree new_decl, tree delete_decl)
   void *np = NULL, *dp = NULL;
   demangle_component *ndc = cplus_demangle_v3_components (new_str, 0, &np);
   demangle_component *ddc = cplus_demangle_v3_components (del_str, 0, &dp);
-  bool mismatch = ndc && ddc && new_delete_mismatch_p (*ndc, *ddc);
+
+  /* Sometimes, notably quite often with coroutines, 'operator new' is
+     templated.  However, template arguments can't change whether a given
+     new/delete is a singleton or array one, nor what it is a member of, so
+     the template arguments can be safely ignored for the purposes of checking
+     for mismatches.   */
+
+  auto strip_dc_template = [] (demangle_component* dc)
+  {
+    if (dc->type == DEMANGLE_COMPONENT_TEMPLATE)
+      dc = dc->u.s_binary.left;
+    return dc;
+  };
+
+  bool mismatch = (ndc && ddc
+		   && new_delete_mismatch_p (*strip_dc_template (ndc),
+					     *strip_dc_template (ddc)));
   free (np);
   free (dp);
   return mismatch;
diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-9.C b/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-9.C
new file mode 100644
index 0000000..d431f40
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wmismatched-new-delete-9.C
@@ -0,0 +1,47 @@
+/* { dg-do compile { target c++11 } } */
+/* { dg-additional-options "-Wmismatched-new-delete" } */
+/* PR middle-end/109224 */
+/* Verify that we consider templated operator new matching with its operator
+   delete.  */
+
+#include <new>
+
+struct foo
+{
+  template<typename... Args>
+  void* operator new (std::size_t sz, Args&&...);
+  template<typename... Args>
+  void* operator new[] (std::size_t sz, Args&&...);
+
+  void operator delete (void* x);
+  void operator delete[] (void* x);
+
+  template<typename... Args>
+  void operator delete (void* x, Args&&...);
+  template<typename... Args>
+  void operator delete[] (void* x, Args&&...);
+};
+
+void
+f ()
+{
+  delete (new (123, true) foo);
+  delete[] (new (123, true) foo[123]);
+
+  delete (new (123, true) foo[123]);
+  // { dg-warning "Wmismatched-new-delete" "" { target *-*-* } {.-1} }
+  // { dg-note "returned from" "" { target *-*-* } {.-2} }
+  delete[] (new (123, true) foo);
+  // { dg-warning "Wmismatched-new-delete" "" { target *-*-* } {.-1} }
+  // { dg-note "returned from" "" { target *-*-* } {.-2} }
+
+  foo::operator delete (foo::operator new (1, 123, true), 123, true);
+  foo::operator delete[] (foo::operator new[] (123, 123, true), 123, true);
+
+  foo::operator delete (foo::operator new[] (123, 123, true), 123, true);
+  // { dg-warning "Wmismatched-new-delete" "" { target *-*-* } {.-1} }
+  // { dg-note "returned from" "" { target *-*-* } {.-2} }
+  foo::operator delete[] (foo::operator new (1, 123, true), 123, true);
+  // { dg-warning "Wmismatched-new-delete" "" { target *-*-* } {.-1} }
+  // { dg-note "returned from" "" { target *-*-* } {.-2} }
+}
diff --git a/gcc/testsuite/g++.dg/warn/pr109224.C b/gcc/testsuite/g++.dg/warn/pr109224.C
new file mode 100644
index 0000000..4b610222
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/pr109224.C
@@ -0,0 +1,25 @@
+// { dg-do compile { target c++20 } }
+#include <coroutine>
+
+struct Task {
+    struct promise_type {
+        std::suspend_never initial_suspend() { return {}; }
+        std::suspend_never final_suspend() noexcept { return {}; }
+        void unhandled_exception() { throw; }
+        Task get_return_object() { return {}; }
+        void return_void() {}
+
+        template<class I>
+        void* operator new(std::size_t sz, I);
+
+        void operator delete(void* ptr, std::size_t);
+    };
+};
+
+Task f(int) {
+    co_return;
+}
+
+int main() {
+    f(42);
+}