On 2/8/23 13:01, Marek Polacek wrote:
(This may not be a complete fix but I got stuck so I'm posting what
I have, which at least fixes the ICE.)
We ICE on the simple:
struct X { const X* x = this; };
constexpr const X& x = X{};
where store_init_value initializes 'x' with
&TARGET_EXPR <D.2768, {.x=(const struct X *) &<PLACEHOLDER_EXPR struct X>}>
but we must lifetime-extend via extend_ref_init_temps and we get
_ZGR1x_.x = (const struct X *) &<PLACEHOLDER_EXPR struct X> >>>;, (const struct X
&) &_ZGR1x_;
Since 'x' was declared constexpr, we do cxx_constant_init and we hit
the preeval code added in r269003 while evaluating the INIT_EXPR:
_ZGR1x_.x = (const struct X *) &<PLACEHOLDER_EXPR struct X> >>>
but we have no ctx.ctor or ctx.object here so lookup_placeholder won't
find anything that could replace X and we ICE on
7861 /* A placeholder without a referent. We can get here when
7862 checking whether NSDMIs are noexcept, or in massage_init_elt;
7863 just say it's non-constant for now. */
7864 gcc_assert (ctx->quiet);
because cxx_constant_init means !ctx->quiet. It's not correct that
there isn't a referent. I think the following patch is a pretty
straightforward fix: pass the _ZGR var down to maybe_constant_init so
that it can replace the PLACEHOLDER_EXPR with _ZGR1x_.
What I wasn't able to make work is the commented assert in the test.
It doesn't pass because we complain that _ZGR1x_ isn't a constexpr
variable,
That sounds like we aren't (correctly) implementing
https://eel.is/c++draft/expr.const#4.7
but making it so would just result in "used in its own
initializer" (which is true).
True, but not in the sense it means; its initializer doesn't depend on
its (uninitialized) value.
I notice that while clang++ compiles
the assert fine, MSVC++/icc reject it as non-constant. So maybe we
don't have to/shouldn't make it work.
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
PR c++/107079
gcc/cp/ChangeLog:
* call.cc (set_up_extended_ref_temp): Pass var to maybe_constant_init.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/constexpr-nsdmi2.C: New test.
---
gcc/cp/call.cc | 2 +-
gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C | 9 +++++++++
2 files changed, 10 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index f7c5d9da94b..a0afab9b26a 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -13583,7 +13583,7 @@ set_up_extended_ref_temp (tree decl, tree expr, vec<tree,
va_gc> **cleanups,
/* If the initializer is constant, put it in DECL_INITIAL so we get
static initialization and use in constant expressions. */
- init = maybe_constant_init (expr);
+ init = maybe_constant_init (expr, var);
We should also pass true for manifestly_const_eval as in store_init_value.
/* As in store_init_value. */
init = cp_fully_fold (init);
if (TREE_CONSTANT (init))
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C
b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C
new file mode 100644
index 00000000000..6dbb7eb739a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-nsdmi2.C
@@ -0,0 +1,9 @@
+// PR c++/107079
+// { dg-do compile { target c++11 } }
+
+struct X {
+ const X* x = this;
+};
+constexpr const X& x = X{};
+// TODO: Should the assert pass?
+//static_assert(x.x == &x);
base-commit: 77bb54b1b07add45007c664724b726541d672ef3
