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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109756] "internal compiler error: tree check" when using
 the [[assume]] attribute with pack expansion
Date: Sat, 06 May 2023 16:54:37 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109756

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p1774r8.pdf
paper says in the introductory part:
We could therefore hypothetically permit the assume attribute to directly
support pack expansion:
template <int... args>
void f() {
[[assume(args >=3D 0)...]];
}
However, we do not propose this. It would require substantial additional wo=
rk
for a very rare use
case. Note that this can instead be expressed with a fold expression, which=
 is
equivalent to the
above and works out of the box without any extra effort:
template <int... args>
void f() {
[[assume(((args >=3D 0) && ...))]];
}

http://eel.is/c++draft/dcl.attr#grammar-4 says:
"In an attribute-list, an ellipsis may appear only if that attribute's
specification permits it."
And I don't see it being explicitly permitted for any of the standard attri=
bute
(except for alignas which uses a different syntax).
So, I think this is invalid and we should reject it.=