[Bug c++/103183] New: ind[arr] produces an lvalue when arr is an array xvalue

[Bug c++/103183] New: ind[arr] produces an lvalue when arr is an array xvalue

[de34 at live dot cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103183

            Bug ID: 103183
           Summary: ind[arr] produces an lvalue when arr is an array
                    xvalue
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Keywords: accepts-invalid, rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: de34 at live dot cn
  Target Milestone: ---

With gcc 10 and later versions, the following program compiles in C++11/14
modes, but fails to compile in C++17 and later modes. It compiles in C++17 and
later modes if "int&&" is replaced with "int&" (which is wrong according to
[expr.sub]/2).

#include <type_traits>
#include <utility>

int main()
{
    int arr[]{0};
    static_assert(std::is_same<decltype(0[std::move(arr)]), int&&>::value, "");
}

It seems that arr[ind] doesn't suffer from this bug.

Gcc 9 correctly produced an xvalue in this case.

wandbox links (rejected valid code):
gcc 12.0 (-std=c++17): https://wandbox.org/permlink/HvNaq9T4J7oeYflt
gcc 12.0 (-std=c++14): https://wandbox.org/permlink/S3dhGvKr3aD5OeOW
gcc 10.1 (-std=c++17): https://wandbox.org/permlink/NzqYCtytSUW4oZjR
gcc 10.1 (-std=c++14): https://wandbox.org/permlink/LviIophRujplHx6o
gcc  9.3 (-std=c++17): https://wandbox.org/permlink/JkCQHBdc3xqDSG9s

wandbox links (accepted invalid code, with "int&&" replaced with "int&"):
gcc 12.0 (-std=c++17): https://wandbox.org/permlink/JkCQHBdc3xqDSG9s
gcc 10.1 (-std=c++17): https://wandbox.org/permlink/Yr3Vl2mbeDzGi02v

[Bug c++/103183] ind[arr] produces an lvalue when arr is an array xvalue

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103183

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There has to be C++ defect report about this.  Because clang has the behavior
you are requesting but ICC, MSVC all act the same as GCC.

[Bug c++/103183] ind[arr] produces an lvalue when arr is an array xvalue

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103183

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Found it PR 79832.

[Bug c++/103183] ind[arr] produces an lvalue when arr is an array xvalue

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103183

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Found it PR 79832.

Well DR 1213, http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1213

[Bug c++/103183] [11/12/13/14 Regression] ind[arr] produces an lvalue when arr is an array xvalue

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103183

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
            Summary|ind[arr] produces an lvalue |[11/12/13/14 Regression]
                   |when arr is an array xvalue |ind[arr] produces an lvalue
                   |                            |when arr is an array xvalue
   Target Milestone|---                         |11.5

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Like PR103185, this one also started with r10-3793-g1a37b6d9a7e57c

[Bug c++/103183] [11/12/13/14 Regression] ind[arr] produces an lvalue when arr is an array xvalue

[de34 at live dot cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103183

--- Comment #5 from Jiang An <de34 at live dot cn> ---
Seems fixed together by commit
r14-6753-g8dfc52a75d4d6c8be1c61b4aa831b1812b14a10e.

https://godbolt.org/z/on3K451a5

[Bug c++/103183] [11/12/13/14 Regression] ind[arr] produces an lvalue when arr is an array xvalue

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103183

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |law at gcc dot gnu.org
         Resolution|---                         |FIXED

--- Comment #6 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Per c#5.