[llvm-bugs] [Bug 47954] New: "Variable must be initialized by a constant expression" on std::min/max

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=47954

            Bug ID: 47954
           Summary: "Variable must be initialized by a constant
                    expression" on std::min/max
           Product: clang
           Version: 11.0
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++17
          Assignee: unassignedclangbugs at nondot.org
          Reporter: dmitriy.ovdienko at gmail.com
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

I cannot compile the following code:

```cpp
#include <algorithm>

static constexpr auto x = {1, 2, 3};
static constexpr auto y = std::min(x);
```

The error is:
=======================================================
bad.cpp:5:23: error: constexpr variable 'y' must be initialized by a constant
expression
static constexpr auto y = std::min(x);
                      ^   ~~~~~~~~~~~
C:\msys64\mingw64\include\c++\10.2.0\bits/predefined_ops.h:43:16: note: read of
temporary is not allowed in a constant expression outside the expression that
created the
      temporary
      { return *__it1 < *__it2; }
               ^
C:\msys64\mingw64\include\c++\10.2.0\bits/stl_algo.h:5636:6: note: in call to
'&__comp->operator()(&{1, 2, 3}[1], &{1, 2, 3}[0])'
        if (__comp(__first, __result))
            ^
C:\msys64\mingw64\include\c++\10.2.0\bits/stl_algo.h:5660:14: note: in call to
'__min_element(&{1, 2, 3}[1], &{1, 2, 3}[3], {})'
      return _GLIBCXX_STD_A::__min_element(__first, __last,
             ^
C:\msys64\mingw64\include\c++\10.2.0\x86_64-w64-mingw32\bits/c++config.h:400:25:
note: expanded from macro '_GLIBCXX_STD_A'
# define _GLIBCXX_STD_A std
                        ^
C:\msys64\mingw64\include\c++\10.2.0\bits/stl_algo.h:3469:15: note: in call to
'min_element(&{1, 2, 3}[0], &{1, 2, 3}[3])'
    { return *std::min_element(__l.begin(), __l.end()); }
              ^
bad.cpp:5:27: note: in call to 'min({&{1, 2, 3}[0], 3})'
static constexpr auto y = std::min(x);
                          ^
bad.cpp:3:27: note: temporary created here
static constexpr auto x = {1, 2, 3};

=======================================================

However following code does compile:

```cpp
#include <algorithm>
static constexpr auto y = std::min({1, 2, 3});
```

OS: Windows 10
Distribution: MSys2 (https://www.msys2.org/)
clang version 10.0.1 (https://github.com/Alexpux/MINGW-packages.git
94b687508346d10cec7e8c769785f73da18b4e54)
Target: x86_64-w64-windows-gnu
Thread model: posix
InstalledDir: C:\msys64\mingw64\bin

The code above does not compile on clang 11 and trunk on https://godbolt.org/
too.

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