NVidia nvc++ compiler with O2 optimization leads to unknown token error during parsing

[franzpoeschel]

I don't know if this is a compiler issue or an issue with the toml11 library, but with optimization level -O2 in nvc++, the toml11 will often fail parsing strings due to unknown tokens appearing. By putting printf statements in the toml11 source code, I found out that the unknown token appears to be a linefeed.

To reproduce:
I installed the NVidia compilers into an Ubuntu 20.04, using the following two packages:

1. https://developer.download.nvidia.com/hpc-sdk/21.5/nvhpc-2021_21.5_amd64.deb
2. https://developer.download.nvidia.com/hpc-sdk/21.5/nvhpc-21-5_21.5_amd64.deb

If not yet installed, the environment-modules OS package is needed to activate the compiler environment thereafter via:

> source /etc/profile.d/modules.sh 
> module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/21.5 
> which nvc++
/opt/nvidia/hpc_sdk/Linux_x86_64/21.5/compilers/bin/nvc++
> nvc++ --version

nvc++ 21.5-0 LLVM 64-bit target on x86-64 Linux -tp skylake 
NVIDIA Compilers and Tools
Copyright (c) 2021, NVIDIA CORPORATION.  All rights reserved.

I checked out toml11 at the v3.7.1 tag (the issue can also be reproduced on the latest master, 22db720 commit) and compiled the following test program:

#include <toml.hpp>

int main()
{
    constexpr char const *raw = R"(
left = "val"
right = "val"
    )";
    constexpr std::ios::openmode openmode = std::ios_base::in;
    std::istringstream istream(raw, openmode);
    toml::value tomlVal = toml::parse(istream);
}

Compilation and invocation:

> nvc++  -I"$HOME/git-repos/toml11" -O2 --c++17 -o main main.cpp
> ./main 
terminate called after throwing an instance of 'toml::syntax_error'
  what():  [error] toml::parse_value: unknown token appeared
 --> unknown file
   |
 2 | left = "val"
   |        ^--- unknown
Aborted (core dumped)
> nvc++  -I"$HOME/git-repos/toml11" -O1 --c++17 -o main main.cpp
> ./main

The second invocation, compiled with -O1 finishes cleanly.

[franzpoeschel]

I have tried this again with the recent NVidia developer kit (see installation instructions below). The issue seems to be fixed.

$ curl https://developer.download.nvidia.com/hpc-sdk/ubuntu/DEB-GPG-KEY-NVIDIA-HPC-SDK | sudo gpg --dearmor -o /usr/share/keyrings/nvidia-hpcsdk-archive-keyring.gpg
$ echo 'deb [signed-by=/usr/share/keyrings/nvidia-hpcsdk-archive-keyring.gpg] https://developer.download.nvidia.com/hpc-sdk/ubuntu/amd64 /' | sudo tee /etc/apt/sources.list.d/nvhpc.list
$ sudo apt-get update -y
$ sudo apt-get install -y nvhpc-23-1

Issue only comes up on NVHPC 2021 with optimization O2 or O3:

> for i in ./main_*; do echo "$i"; "$i"; done
./main_2021_O0
./main_2021_O2
terminate called after throwing an instance of 'toml::syntax_error'
  what():  [error] toml::parse_value: unknown token appeared
 --> unknown file
   |
 2 | left = "val"
   |        ^--- unknown
Aborted (core dumped)
./main_2023_O0
./main_2023_O2
./main_2023_O3