[Bug c++/99460] [C++20] Template with complex non-type argument re-uses different specialisation

["gcc.mexon at spamgourmet dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99460

--- Comment #1 from mexon <gcc.mexon at spamgourmet dot com> ---
Here's a transcript showing the platform (Ubuntu 20.10 in a virtual machine)
and output of g++ -v -save-temps:

$ vagrant init ubuntu/groovy64
$ vagrant up
$ ssh 127.0.0.1

vagrant@ubuntu-groovy:~$ sudo apt install build-essential bison flex
libgmp3-dev libmpc-dev libmpfr-dev texinfo
vagrant@ubuntu-groovy:~$ wget
ftp://ftp.fu-berlin.de/unix/languages/gcc/releases/gcc-10.2.0/gcc-10.2.0.tar.gz
vagrant@ubuntu-groovy:~$ tar xzf gcc-10.2.0.tar.gz 
vagrant@ubuntu-groovy:~$ cd gcc-10.2.0
vagrant@ubuntu-groovy:~/gcc-10.2.0$ ./contrib/download_prerequisites
vagrant@ubuntu-groovy:~/gcc-10.2.0$ cd ..
vagrant@ubuntu-groovy:~$ mkdir build-gcc
vagrant@ubuntu-groovy:~$ cd build-gcc
vagrant@ubuntu-groovy:~/build-gcc$ 
vagrant@ubuntu-groovy:~/build-gcc$ export PREFIX=$HOME/install-gcc
vagrant@ubuntu-groovy:~/build-gcc$ ../gcc-10.2.0/configure --prefix="$PREFIX"
--disable-nls --enable-languages=c,c++ --disable-multilib
vagrant@ubuntu-groovy:~/build-gcc$ make -j8
vagrant@ubuntu-groovy:~/build-gcc$ make install
vagrant@ubuntu-groovy:~/build-gcc$ cd ..
vagrant@ubuntu-groovy:~$ export PATH=$PREFIX/bin:$PATH
vagrant@ubuntu-groovy:~$ g++ -v -save-temps -Wall --std=c++2a
builder_simplified.cpp
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-10.2.0/configure --prefix=/home/vagrant/install-gcc
--disable-nls --enable-languages=c,c++ --disable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.2.0 (GCC) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c++2a' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 /home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/cc1plus -E
-quiet -v -imultiarch x86_64-linux-gnu -D_GNU_SOURCE builder_simplified.cpp
-mtune=generic -march=x86-64 -std=c++2a -Wall -fpch-preprocess -o
builder_simplified.ii
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../x86_64-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:

/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../include/c++/10.2.0

/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../include/c++/10.2.0/x86_64-pc-linux-gnu

/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../include/c++/10.2.0/backward
 /home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include
 /usr/local/include
 /home/vagrant/install-gcc/include
 /home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c++2a' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 /home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/cc1plus
-fpreprocessed builder_simplified.ii -quiet -dumpbase builder_simplified.cpp
-mtune=generic -march=x86-64 -auxbase builder_simplified -Wall -std=c++2a
-version -o builder_simplified.s
GNU C++17 (GCC) version 10.2.0 (x86_64-pc-linux-gnu)
        compiled by GNU C version 10.2.0, GMP version 6.1.0, MPFR version
3.1.4, MPC version 1.0.3, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++17 (GCC) version 10.2.0 (x86_64-pc-linux-gnu)
        compiled by GNU C version 10.2.0, GMP version 6.1.0, MPFR version
3.1.4, MPC version 1.0.3, isl version isl-0.18-GMP

GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 431465f3c3fef2337a2db16592d4b8cd
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c++2a' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 as -v --64 -o builder_simplified.o builder_simplified.s
GNU assembler version 2.35.1 (x86_64-linux-gnu) using BFD version (GNU Binutils
for Ubuntu) 2.35.1
COMPILER_PATH=/home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/:/home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/:/home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/:/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/:/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/
LIBRARY_PATH=/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/:/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../lib64/:/lib/x86_64-linux-gnu/:/lib/../lib64/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib64/:/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c++2a' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
 /home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/collect2
-plugin
/home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/liblto_plugin.so
-plugin-opt=/home/vagrant/install-gcc/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/lto-wrapper
-plugin-opt=-fresolution=builder_simplified.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 --eh-frame-hdr -m elf_x86_64 -dynamic-linker
/lib64/ld-linux-x86-64.so.2 /lib/x86_64-linux-gnu/crt1.o
/lib/x86_64-linux-gnu/crti.o
/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/crtbegin.o
-L/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0
-L/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../../../lib64
-L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu
-L/usr/lib/../lib64
-L/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/../../..
builder_simplified.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/home/vagrant/install-gcc/lib/gcc/x86_64-pc-linux-gnu/10.2.0/crtend.o
/lib/x86_64-linux-gnu/crtn.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-Wall' '-std=c++2a' '-shared-libgcc'
'-mtune=generic' '-march=x86-64'
vagrant@ubuntu-groovy:~$ ./a.out
a.out: builder_simplified.cpp:46: int main(): Assertion `flags2[1]' failed.
Aborted (core dumped)