Unused `sycl::accessor` detected only when created with `buffer.get_access(...)`

Describe the bug

It appears that icpx is able to detect unused accessors only when they are created with buffer.get_access(...). For example, creating them with sycl::accessor{buffer, ...} does not generate any warning.

To reproduce

I have this simple program:

#include <iostream>
#include <vector>
#include <numeric>

#include <sycl/sycl.hpp>

int main() {
    const size_t n = 10;
    std::vector<int> x(n);

    std::iota(x.begin(), x.end(), 1);

    sycl::queue q{sycl::default_selector_v};

    {
        auto x_buf = sycl::buffer<int, 1>{x.data(), sycl::range<1>{n}};

        q.submit([&](sycl::handler& cgh) {
            sycl::accessor x_acc = x_buf.get_access(cgh, sycl::read_write);
            auto unused_acc = sycl::accessor{x_buf, cgh, sycl::read_write};

            cgh.parallel_for(sycl::range<1>{n}, [=](sycl::id<1> idx) {
                x_acc[idx] *= 2;
            });
        });

        q.wait_and_throw();
    }

    for(size_t i{0}; i < n; i++) {
        std::cout << " x[" << i << "] = " << x.at(i) << std::endl;
    }

    return 0;
}

with an unused accessor which doesn't get detected when I compile with icpx --std=c++17 -fsycl -Wall -Wextra -Wpedantic -Werror -Wshadow main.cpp -o main.x.

However, If I change it to:

#include <iostream>
#include <vector>
#include <numeric>

#include <sycl/sycl.hpp>

int main() {
    const size_t n = 10;
    std::vector<int> x(n);

    std::iota(x.begin(), x.end(), 1);

    sycl::queue q{sycl::default_selector_v};

    {
        auto x_buf = sycl::buffer<int, 1>{x.data(), sycl::range<1>{n}};

        q.submit([&](sycl::handler& cgh) {
            sycl::accessor x_acc = x_buf.get_access(cgh, sycl::read_write);
            sycl::accessor unused_acc = x_buf.get_access(cgh, sycl::read_write);

            cgh.parallel_for(sycl::range<1>{n}, [=](sycl::id<1> idx) {
                x_acc[idx] *= 2;
            });
        });

        q.wait_and_throw();
    }

    for(size_t i{0}; i < n; i++) {
        std::cout << " x[" << i << "] = " << x.at(i) << std::endl;
    }

    return 0;
}

It gets detected and the compilation fails with:

main.cpp:20:19: error: unused variable 'unused_acc' [-Werror,-Wunused-variable]
   20 |                         sycl::accessor unused_acc = x_buf.get_access(cgh, sycl::read_write);
      |                                        ^~~~~~~~~~
1 error generated.

Environment

OS: Ubuntu 22.04.3
Target device and vendor: Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz

DPC++ version:

Intel(R) oneAPI DPC++/C++ Compiler 2024.2.1 (2024.2.1.20240711)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /opt/intel/oneapi/compiler/2024.2/bin/compiler
Configuration file: /opt/intel/oneapi/compiler/2024.2/bin/compiler/../icpx.cfg

Dependencies version:


[opencl:cpu][opencl:0] Intel(R) OpenCL, Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz OpenCL 3.0 (Build 0) [2024.18.7.0.11_160000]
[opencl:gpu][opencl:1] Intel(R) OpenCL Graphics, Intel(R) UHD Graphics 620 OpenCL 3.0 NEO  [23.30.26918.9]

Platforms: 2 Platform [#1]: Version : OpenCL 3.0 LINUX Name : Intel(R) OpenCL Vendor : Intel(R) Corporation Devices : 1 Device [#0]: Type : cpu Version : OpenCL 3.0 (Build 0) Name : Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz Vendor : Intel(R) Corporation Driver : 2024.18.7.0.11_160000 Aspects : cpu fp16 fp64 online_compiler online_linker queue_profiling usm_device_allocations usm_host_allocations usm_shared_allocations usm_system_allocations usm_atomic_host_allocations usm_atomic_shared_allocations atomic64 ext_oneapi_srgb ext_oneapi_native_assert ext_intel_legacy_image ext_oneapi_ballot_group ext_oneapi_fixed_size_group ext_oneapi_opportunistic_group ext_oneapi_tangle_group info::device::sub_group_sizes: 4 8 16 32 64 Platform [#2]: Version : OpenCL 3.0 Name : Intel(R) OpenCL Graphics Vendor : Intel(R) Corporation Devices : 1 Device [#1]: Type : gpu Version : OpenCL 3.0 NEO Name : Intel(R) UHD Graphics 620 Vendor : Intel(R) Corporation Driver : 23.30.26918.9 Aspects : gpu fp16 fp64 online_compiler online_linker queue_profiling usm_device_allocations usm_host_allocations usm_shared_allocations atomic64 ext_oneapi_srgb ext_intel_device_id ext_intel_legacy_image ext_intel_esimd ext_oneapi_ballot_group ext_oneapi_fixed_size_group ext_oneapi_opportunistic_group ext_oneapi_tangle_group info::device::sub_group_sizes: 8 16 32 default_selector() : gpu, Intel(R) OpenCL Graphics, Intel(R) UHD Graphics 620 OpenCL 3.0 NEO [23.30.26918.9] accelerator_selector() : No device of requested type available. Please chec... cpu_selector() : cpu, Intel(R) OpenCL, Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz OpenCL 3.0 (Build 0) [2024.18.7.0.11_160000] gpu_selector() : gpu, Intel(R) OpenCL Graphics, Intel(R) UHD Graphics 620 OpenCL 3.0 NEO [23.30.26918.9] custom_selector(gpu) : gpu, Intel(R) OpenCL Graphics, Intel(R) UHD Graphics 620 OpenCL 3.0 NEO [23.30.26918.9] custom_selector(cpu) : cpu, Intel(R) OpenCL, Intel(R) Core(TM) i5-8265U CPU @ 1.60GHz OpenCL 3.0 (Build 0) [2024.18.7.0.11_160000] custom_selector(acc) : No device of requested type available. Please chec...



### Additional context

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intel / llvm