[Bug c++/63217] template conversion operator returning const reference not used for conversion in some cases

[vz at quantitativesystems dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63217

--- Comment #2 from Edward <vz at quantitativesystems dot com> ---
I can confirm the bug in version 6.3.0 freshly built:

(found this bug researching for a similar bug I am reporting)

Using built-in specs.
COLLECT_GCC=/home/h/packages/gcc-6.3.0/bin/g++
COLLECT_LTO_WRAPPER=/home/h/packages/gcc-6.3.0/libexec/gcc/x86_64-pc-linux-gnu/6.3.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-6.3.0/configure --prefix=/home/h/packages/gcc-6.3.0
--enable-languages=c++
Thread model: posix
gcc version 6.3.0 (GCC) 
COLLECT_GCC_OPTIONS='-v' '-std=c++1z' '-shared-libgcc' '-mtune=generic'
'-march=x86-64'
 /home/h/packages/gcc-6.3.0/libexec/gcc/x86_64-pc-linux-gnu/6.3.0/cc1plus
-quiet -v -D_GNU_SOURCE src/f5.cpp -quiet -dumpbase f5.cpp -mtune=generic
-march=x86-64 -auxbase f5 -std=c++1z -version -o /tmp/ccSkJoqY.s
GNU C++14 (GCC) version 6.3.0 (x86_64-pc-linux-gnu)
    compiled by GNU C version 6.3.0, GMP version 5.1.1, MPFR version 3.1.1, MPC
version 1.0.1, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory
"/home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:

/home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../include/c++/6.3.0

/home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../include/c++/6.3.0/x86_64-pc-linux-gnu

/home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/../../../../include/c++/6.3.0/backward
 /home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/include
 /usr/local/include
 /home/h/packages/gcc-6.3.0/include
 /home/h/packages/gcc-6.3.0/lib/gcc/x86_64-pc-linux-gnu/6.3.0/include-fixed
 /usr/include
End of search list.
GNU C++14 (GCC) version 6.3.0 (x86_64-pc-linux-gnu)
    compiled by GNU C version 6.3.0, GMP version 5.1.1, MPFR version 3.1.1, MPC
version 1.0.1, isl version none
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 80f12065068033b5f76b36dba8781986
src/f5.cpp: In function ‘int main()’:
src/f5.cpp:8:18: error: cannot convert ‘foo’ to ‘int’ in initialization
     int t((foo()));