On Sat, Oct 03, 2026 at 09:32:38AM +0200, Jason Merrill wrote:
> On 10/2/26 11:19 PM, Marek Polacek wrote:
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> >
> > -- >8 --
> > In this PR we have
> >
> > consteval{
> > const int* m = std::allocator<int>().allocate(1);
> > std::meta::reflect_constant(m);
> > }
> >
> > which is invalid: reflect_constant throws meta::exception unless the
> > template-id TCls<V> would be valid ([meta.reflection.result]/5).
> >
> > [temp.arg.nontype]/1 wants the invented declaration T x = E; to satisfy
> > the semantic constraints of a constexpr variable with static storage
> > duration.
> >
> > [dcl.constexpr]/6: A constexpr variable shall be constant-initializable.
> >
> > [expr.const.init]/4: A variable v is constant-initializable if [...]
> > -- the full-expression of its initialization is a constant expression
> > -- if x has static or thread storage duration, x is constexpr-representable
> > [...]
> >
> > [expr.const.init]/3: x is constexpr-representable at P if every object
> > that a constituent value of x points to is constexpr-referenceable
> > from P.
> >
> > [expr.const.init]/2: An object o is constexpr-referenceable from a point P
> > if ... it has static storage duration, or automatic storage duration with
> > certain scope conditions.
> >
> > But the array object allocate gave us has dynamic storage duration as per
> > [allocator.members]/5 -> it's not constexpr-referenceable -> this TCls<V>
> > is invalid so reflect_constant should throw. But we trip on the assert
> > because decl is a heap variable.
> >
> > There is no way AFAIK to check the failure sooner than
> > invalid_tparm_referent_p
> > (here we are called from eval_reflect_constant) so this patch extends the
> > existing assert.
> >
> > PR c++/125649
> >
> > gcc/cp/ChangeLog:
> >
> > * constexpr.cc (addr_of_non_const_var): Use heap_var_p.
> > (non_const_var_error): Likewise.
> > (cxx_eval_constant_expression): Likewise.
> > (find_heap_var_refs): Likewise.
> > (heap_var_p): New.
> > * cp-tree.h (heap_var_p): Declare.
> > * pt.cc (invalid_tparm_referent_p): Add heap_var_p to an
> > assert.
> >
> > gcc/testsuite/ChangeLog:
> >
> > * g++.dg/reflect/reflect_constant10.C: New test.
> > ---
> > gcc/cp/constexpr.cc | 35 +++++++++--------
> > gcc/cp/cp-tree.h | 1 +
> > gcc/cp/pt.cc | 18 ++++++---
> > .../g++.dg/reflect/reflect_constant10.C | 38 +++++++++++++++++++
> > 4 files changed, 68 insertions(+), 24 deletions(-)
> > create mode 100644 gcc/testsuite/g++.dg/reflect/reflect_constant10.C
> >
> > diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
> > index 31ef5bf1111..a99659f9685 100644
> > --- a/gcc/cp/constexpr.cc
> > +++ b/gcc/cp/constexpr.cc
> > @@ -3276,10 +3276,7 @@ addr_of_non_const_var (tree *tp, int *walk_subtrees,
> > void *data)
> > if (tree var = get_base_address (TREE_OPERAND (*tp, 0)))
> > if (VAR_P (var) && TREE_STATIC (var))
> > {
> > - if (DECL_NAME (var) == heap_uninit_identifier
> > - || DECL_NAME (var) == heap_identifier
> > - || DECL_NAME (var) == heap_vec_uninit_identifier
> > - || DECL_NAME (var) == heap_vec_identifier)
> > + if (heap_var_p (var))
>
> Why don't we want to include _deleted in all cases?
I didn't want to change behavior by introducing that helper. E.g.,
in non_const_var_error the second branch would be dead if the first
one accepted _deleted, and cxx_eval_constant_expression would also
behave differently for the void* -> T* cast.
Marek
