Re: [PATCH 1/2] c++: Make __builtin_launder reject invalid types [PR116673]

[Jason Merrill]

On 9/12/24 4:49 AM, Jonathan Wakely wrote:
Tested x86_64-linux. OK for trunk?
-- >8 --

The standard says that std::launder is ill-formed for function pointers
and cv void pointers, so there's no reason for __builtin_launder to
accept them. This change allows implementations of std::launder to defer
to the built-in for error checking, although libstdc++ will continue to
diagnose it directly for more user-friendly diagnostics.

        PR c++/116673

gcc/cp/ChangeLog:

        * semantics.cc (finish_builtin_launder): Diagnose function
        pointers and cv void pointers.

gcc/testsuite/ChangeLog:

        * g++.dg/cpp1z/launder10.C: New test.
---
  gcc/cp/semantics.cc                    | 17 +++++++++++++----
  gcc/testsuite/g++.dg/cpp1z/launder10.C | 15 +++++++++++++++
  2 files changed, 28 insertions(+), 4 deletions(-)
  create mode 100644 gcc/testsuite/g++.dg/cpp1z/launder10.C

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 63212afafb3..b194b01f865 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -13482,11 +13482,20 @@ finish_builtin_launder (location_t loc, tree arg, 
tsubst_flags_t complain)
      arg = decay_conversion (arg, complain);
    if (error_operand_p (arg))
      return error_mark_node;
-  if (!type_dependent_expression_p (arg)
-      && !TYPE_PTR_P (TREE_TYPE (arg)))
+  if (!type_dependent_expression_p (arg))
      {
-      error_at (loc, "non-pointer argument to %<__builtin_launder%>");
-      return error_mark_node;
+      tree type = TREE_TYPE (arg);
+      if (!TYPE_PTR_P (type))
+       {
+         error_at (loc, "non-pointer argument to %<__builtin_launder%>");
+         return error_mark_node;
+       }
+      else if (!object_type_p (TREE_TYPE (type)))
+       {
+         // std::launder is ill-formed for function and cv void pointers.
+         error_at (loc, "invalid argument to %<__builtin_launder%>");

Let's be more specific by combining both errors into

"type %qT of argument to %<__builtin_launder"> is not a pointer to 
object type"

The tests can also be combined to !TYPE_PTROB_P.

OK with that change.

+         return error_mark_node;
+       }
      }
    if (processing_template_decl)
      arg = orig_arg;
diff --git a/gcc/testsuite/g++.dg/cpp1z/launder10.C 
b/gcc/testsuite/g++.dg/cpp1z/launder10.C
new file mode 100644
index 00000000000..7c15eeb891f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/launder10.C
@@ -0,0 +1,15 @@
+// PR c++/116673
+// { dg-do compile }
+
+void
+bar (void *p)
+{
+  __builtin_launder (bar); // { dg-error {invalid argument to 
'__builtin_launder'} }
+  __builtin_launder (p);   // { dg-error {invalid argument to 
'__builtin_launder'} }
+  const void* cp = p;
+  __builtin_launder (cp);  // { dg-error {invalid argument to 
'__builtin_launder'} }
+  volatile void* vp = p;
+  __builtin_launder (vp);  // { dg-error {invalid argument to 
'__builtin_launder'} }
+  const volatile void* cvp = p;
+  __builtin_launder (cvp); // { dg-error {invalid argument to 
'__builtin_launder'} }
+}