[Bug c++/104031] New: [12 regression] Global nested constructors generate invalid code.

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104031

            Bug ID: 104031
           Summary: [12 regression] Global nested constructors generate
                    invalid code.
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Extracted from original example of nix-2.4 where global constructors register
invalid primops. Single-file example:

// $ cat main.cc
#include <string>
#include <vector>

struct Info {
    std::vector<std::string> args;
    size_t arity = 0;
};

struct RegisterPrimOp
{
    RegisterPrimOp(Info && info) __attribute__((noipa, noinline)) {
        if (info.arity != 0)
            __builtin_trap();
    }
};

static RegisterPrimOp s_op({
    .args = {"path"},
    .arity = 0,
});

int main() {}

# ok:
$ g++-11.2.0 main.cc -o main -O2 && ./main
# bad:
$ g++-12.0.0 main.cc -o main -O2 && ./main
Illegal instruction (core dumped)

Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-12.0.0/bin/g++
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-12.0.0/libexec/gcc/x86_64-unknown-linux-gnu/12.0.0/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 12.0.0 20220109 (experimental) (GCC)

Must be a recent regression. Possibly a close sibling of diagnostic false
positive: https://gcc.gnu.org/PR103984