[llvm-bugs] [Bug 41863] New: [C++17] std:variant fails with libstdc++ from gcc-9.1.0

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=41863

            Bug ID: 41863
           Summary: [C++17] std:variant fails with libstdc++ from
                    gcc-9.1.0
           Product: clang
           Version: 8.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++'17
          Assignee: unassignedclangbugs at nondot.org
          Reporter: orbea at riseup.net
                CC: blitzrakete at gmail.com, erik.pilkington at gmail.com,
                    llvm-bugs at lists.llvm.org, richard-llvm at metafoo.co.uk

Created attachment 21944
  --> https://bugs.llvm.org/attachment.cgi?id=21944&action=edit
variant demo which reproduces the problem

On Slackware64-current gcc was updated from 8.3.0 to 9.1.0 and I found that
clang++ which uses libstdc++ now fails to build C++17 projects which use
'#include <variant>'. The issue does not occur with libc++.

I have attached a small demo which I have found online which can reproduce this
issue, but I first encountered the issue in the current master for dolphin-emu.

https://github.com/dolphin-emu/dolphin/commit/1d5dd5db914d94f3f612c13c6c5e1d5e711b49b5

With the example it can be reproduced:

  clang++ -std=c++17 variant.cpp -o variant -v

While both of these work:

  g++ -std=c++17 variant.cpp -o variant -v
  clang++ -std=c++17 -stdlib=libc++ variant.cpp -o variant -v

In Slackware current llvm is compiled as a single mostly complete package with
these cmake arguments.

cd build
  cmake \
    -DCMAKE_C_COMPILER="clang" \
    -DCMAKE_CXX_COMPILER="clang++" \
    -DCMAKE_C_FLAGS:STRING="$SLKCFLAGS" \
    -DCMAKE_CXX_FLAGS:STRING="$SLKCFLAGS" \
    -DCMAKE_INSTALL_PREFIX=/usr \
    -DLLVM_LIBDIR_SUFFIX=${LIBDIRSUFFIX} \
    -DCMAKE_BUILD_TYPE=Release \
    -DBUILD_SHARED_LIBS=OFF \
    -DCLANG_BUILD_SHARED_LIBS=ON \
    -DLLVM_BUILD_LLVM_DYLIB=ON \
    -DLLVM_LINK_LLVM_DYLIB=ON \
    -DLLVM_USE_LINKER=gold \
    -DLLVM_ENABLE_RTTI=ON \
    -DLLVM_ENABLE_FFI=ON \
    -DLLVM_ENABLE_ASSERTIONS=OFF \
    -DLLVM_USE_OPROFILE=ON \
    -DLLVM_INSTALL_UTILS=ON \
    -DLLVM_BINUTILS_INCDIR=/usr/include \
    -DCLANG_RESOURCE_DIR="../lib${LIBDIRSUFFIX}/clang/${VERSION}" \
    .. || exit 1

For further details please see this link.

https://mirrors.slackware.com/slackware/slackware64-current/source/d/llvm/

I will add further attachments with details.

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