This is a simple reproducer for NVIDIA bug (5840342)[https://developer.nvidia.com/bugs/5840342]

Description

nvcc accepts invalid device code when a constexpr function containing host-only C++ standard library types (e.g. std::: string) is instantiated and called from a CUDA kernel, particularly when using --std=c++20 --expt-relaxed-constexpr. Thee code compiles without diagnostics even though such constructs are not supported in device code. This can lead to silent mii scompilation or undefined behavior at runtime.

Reproducer

A reproducer can be as simple as test.cu:

#include <cstdio>
#include <string>

template <int I>
constexpr void dump() {
        std::string data = std::to_string(I);
        printf("%s\n", data.data());
}

template <int I>
__global__ void kernel() {
        dump<I>();
}

int main() {
        printf("Before\n");
        cudaDeviceSynchronize();
        kernel<42><<<1, 1>>>();
        cudaDeviceSynchronize();
        printf("After\n");
}

Compiling with:

/usr/local/cuda-13.0/bin/nvcc -ccbin /opt/rh/gcc-toolset-14/root/usr/bin/gcc -std=c++20 --expt-relaxed-constexpr test.cu -oo
 test

Investigation indicates additionally that the behavior depends on the host compiler. For example, using nvcc v13.0.88 witt h gcc 11.5.0 produces an expected compilation error, whereas switching to gcc 14.2.1 suppresses the error and allows thh e invalid code to compile.

An an example nvcc 12.9.1 with gcc (GCC) 11.5.0 leads to the correct error message

<source>(17): error: calling a __host__ function("void  ::dump<(int)42> ()") from a __global__ function("kernel<(int)42> "))
 is not allowed

<source>(17): error: identifier "dump<(int)42> " is undefined in device code