On Thu, 12 Sept 2024 at 19:38, Patrick Palka <[email protected]> wrote:
>
> On Thu, 12 Sep 2024, 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%>");
>
> Do we care about making this builtin SFINAE-friendly by guarding these
> errors with tf_error?
I don't think so. I don't think there's any use case for using
__builtin_launder (or std::launder for that matter) in deduction
contexts.
>
> > + 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%>");
> > + 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'} }
> > +}
> > --
> > 2.46.0
> >
> >
>
