[Bug c++/109757] New: Conversion from lvalue to rvalue without error

["jonathan.poelen at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109757

            Bug ID: 109757
           Summary: Conversion from lvalue to rvalue without error
           Product: gcc
           Version: 12.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jonathan.poelen at gmail dot com
  Target Milestone: ---

GCC 12.2.1

$ cat test.cpp

void foo(int&&) {}

int main()
{
  using T = int&&;
  int x = 0;
  T{x}; // ok -> should be error
  foo(T{x}); // ok -> should be error
  //T r{x}; // nok -> is good
}

$ g++ test.cpp

No error, there should be a 2 errors.

$ g++ test.cpp -v -save-temps
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++,d --enable-bootstrap
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--with-build-config=bootstrap-lto --with-linker-hash-style=gnu
--with-system-zlib --enable-__cxa_atexit --enable-cet=auto
--enable-checking=release --enable-clocale=gnu --enable-default-pie
--enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object
--enable-libstdcxx-backtrace --enable-link-serialization=1
--enable-linker-build-id --enable-lto --enable-multilib --enable-plugin
--enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-werror
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.2.1 20230201 (GCC) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64' '-dumpdir' 'a-'
 /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/cc1plus -E -quiet -v -D_GNU_SOURCE
test.cpp -mtune=generic -march=x86-64 -fpch-preprocess -o a-test.ii
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../include/c++/12.2.1

/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../include/c++/12.2.1/x86_64-pc-linux-gnu

/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../include/c++/12.2.1/backward
 /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/include
 /usr/local/include
 /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64' '-dumpdir' 'a-'
 /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/cc1plus -fpreprocessed a-test.ii
-quiet -dumpdir a- -dumpbase test.cpp -dumpbase-ext .cpp -mtune=generic
-march=x86-64 -version -o a-test.s
GNU C++17 (GCC) version 12.2.1 20230201 (x86_64-pc-linux-gnu)
        compiled by GNU C version 12.2.1 20230201, GMP version 6.2.1, MPFR
version 4.2.0, MPC version 1.3.1, isl version isl-0.25-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++17 (GCC) version 12.2.1 20230201 (x86_64-pc-linux-gnu)
        compiled by GNU C version 12.2.1 20230201, GMP version 6.2.1, MPFR
version 4.2.0, MPC version 1.3.1, isl version isl-0.25-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: ab2adc4aa87e9c5b6e6cb24c55e663d5
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64' '-dumpdir' 'a-'
 as -v --64 -o a-test.o a-test.s
GNU assembler version 2.40 (x86_64-pc-linux-gnu) using BFD version (GNU
Binutils) 2.40
COMPILER_PATH=/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/:/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/:/usr/lib/gcc/x86_64-pc-linux-gnu/:/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/:/usr/lib/gcc/x86_64-pc-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/:/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../lib/:/lib/../lib/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64' '-dumpdir' 'a.'
 /usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/collect2 -plugin
/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/liblto_plugin.so
-plugin-opt=/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/lto-wrapper
-plugin-opt=-fresolution=a.res -plugin-opt=-pass-through=-lgcc_s
-plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lc
-plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lgcc --build-id
--eh-frame-hdr --hash-style=gnu -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2 -pie
/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../lib/Scrt1.o
/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../lib/crti.o
/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/crtbeginS.o
-L/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1
-L/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../lib -L/lib/../lib
-L/usr/lib/../lib -L/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../.. a-test.o
-lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/crtendS.o
/usr/lib/gcc/x86_64-pc-linux-gnu/12.2.1/../../../../lib/crtn.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
'-march=x86-64' '-dumpdir' 'a.'

Up to at least 8.5, the code compiles. With MSVC too. Does not compile with
clang: https://godbolt.org/z/o96j5b8oc