On Tue, Jan 18, 2022 at 11:51:31AM -0500, Jason Merrill wrote:
> On 1/18/22 09:26, Jakub Jelinek wrote:
> > On Tue, Jan 18, 2022 at 09:08:03AM -0500, Jason Merrill wrote:
> > > > which makes call a TARGET_EXPR with the dtor in TARGET_EXPR_CLEANUP,
> > > > but then call cxx_constant_value on it. In
> > > > cxx_eval_outermost_constant_expr
> > > > it triggers the:
> > > > else if (TREE_CODE (t) != CONSTRUCTOR)
> > > > {
> > > > r = get_target_expr_sfinae (r, tf_warning_or_error |
> > > > tf_no_cleanup);
> > > > TREE_CONSTANT (r) = true;
> > > > }
> > > > which wraps the CONSTRUCTOR r into a new TARGET_EXPR, but one without
> > > > dtors (I think we need e.g. the TREE_CONSTANT for the callers),
> > > > and finally build_over_call uses that.
> > >
> > > Looks like you added the tf_no_cleanup in r10-3661 (constexpr new). Maybe
> > > that should only be added if TARGET_EXPR_CLEANUP (t) is null?
> >
> > I thought about that, but I'm worried that if the cleanup action
> > is non-empty, then the TREE_CONSTANT (r) = true; after it isn't appropriate,
> > because the TARGET_EXPR has side-effects.
>
> Hmm. If we e.g. pull out a subobject value from the TARGET_EXPR temporary,
> we still need to run the cleanup, so we don't want to optimize the temporary
> away, so not setting TREE_CONSTANT sounds right.
>
> > And the callers like cxx_constant_value_sfinae just return error_mark_node
> > if it isn't set:
> > if (sfinae && !TREE_CONSTANT (r))
> > r = error_mark_node;
>
> Yes. Is that wrong? I guess we need to be more careful about adjusting the
> arguments to cxx_constant_value_sfinae if we still want a constant value.
>
> Perhaps we also still want to set tf_no_cleanup if object is nonnull, since
> in that case we know the prvalue is going to be an initializer rather than a
> temporary.
This passed bootstrap/regtest on i686-linux and bootstrap on
x86_64-linux (regtest still pending):
2022-01-18 Jakub Jelinek <ja...@redhat.com>
PR c++/104055
* constexpr.cc (cxx_eval_outermost_constant_expr): If t is a
TARGET_EXPR with TARGET_EXPR_CLEANUP, use get_target_expr rather
than get_target_expr_sfinae with tf_no_cleanup, and don't set
TREE_CONSTANT.
* g++.dg/cpp2a/consteval27.C: New test.
--- gcc/cp/constexpr.cc.jj 2022-01-18 11:58:59.296986142 +0100
+++ gcc/cp/constexpr.cc 2022-01-18 20:07:28.362485336 +0100
@@ -7821,7 +7821,11 @@ cxx_eval_outermost_constant_expr (tree t
if (TREE_CODE (t) == TARGET_EXPR
&& TARGET_EXPR_INITIAL (t) == r)
return t;
- else if (TREE_CODE (t) != CONSTRUCTOR)
+ else if (TREE_CODE (t) == CONSTRUCTOR)
+ ;
+ else if (TREE_CODE (t) == TARGET_EXPR && TARGET_EXPR_CLEANUP (t))
+ r = get_target_expr (r);
+ else
{
r = get_target_expr_sfinae (r, tf_warning_or_error | tf_no_cleanup);
TREE_CONSTANT (r) = true;
--- gcc/testsuite/g++.dg/cpp2a/consteval27.C.jj 2022-01-18 20:12:55.326006216
+0100
+++ gcc/testsuite/g++.dg/cpp2a/consteval27.C 2022-01-18 20:13:01.442921759
+0100
@@ -0,0 +1,18 @@
+// PR c++/104055
+// { dg-do run { target c++20 } }
+
+int g;
+
+struct A {
+ ~A () { if (a != 17 || b != 26) __builtin_abort (); g = 42; }
+ consteval A () : a (17), b (26) {}
+ int a, b;
+};
+
+int
+main ()
+{
+ A{};
+ if (g != 42)
+ __builtin_abort ();
+}
Jakub
