[llvm-bugs] [Bug 43900] New: Memory Corruption with clang-cl

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43900

            Bug ID: 43900
           Summary: Memory Corruption with clang-cl
           Product: clang
           Version: 9.0
          Hardware: PC
                OS: other
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
          Assignee: unassignedclangbugs at nondot.org
          Reporter: bussyantoine at gmail.com
                CC: blitzrakete at gmail.com, dgregor at apple.com,
                    erik.pilkington at gmail.com, llvm-bugs at lists.llvm.org,
                    richard-llvm at metafoo.co.uk

Created attachment 22766
  --> https://bugs.llvm.org/attachment.cgi?id=22766&action=edit
Reproduction of bug

Hi,

I've encountered a weird bug when using args (https://github.com/Taywee/args)
with clang-cl on Windows 10, in release mode only. Using Visual Studio 2019
debugger, I suspect a memory corruption. Here is the code:

#include "args.hpp"

#include <iostream>

inline auto to_argv(std::vector<std::string>& v)
{
        auto r = std::vector<char*>{};
        for (auto& e : v)
                r.emplace_back(e.data());
        r.emplace_back(nullptr);
        return r;
}

auto other_main(int argc, char* argv[]) -> int
{
        std::cerr << argc << std::endl;
        for(auto i = 0; i < argc; ++i)
                std::cerr << argv[i] << std::endl;
        auto parser = args::ArgumentParser{ "Command Line" };
        auto const help = args::HelpFlag{ parser, "help", "Display this help
menu", {'h', "help"} };
        try
        {
                parser.ParseCLI(argc, argv);
        }
        catch (const args::Help&)
        {
        }
        return 0;
}

int main(int argc, char* argv[])
{
        auto const commands = std::vector<std::string>
        {
                "command",
                "command_2",
        };
        for (auto const& command : commands)
        {
                auto _args = std::vector<std::string>
                {
                        command,
                        "-h",
                };
                for (auto const& a : _args)
                        std::cerr << a << std::endl;
                auto args = to_argv(_args);
                other_main(static_cast<int>(args.size()) - 1, args.data());
        }
}


This should print:

command
-h
2
command
-h
command_2
-h
2
command_2
-h

which it does in debug (or with MSVC or clang on Linux), but it prints:
command
-h
2
command
-h
command_2

2
command_2
-h

In other cases I tested, it prints rubbish, or simply crashes. I attached the
whole self-contained sample, with example cmake commands.

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