[clang-cl] access violation with an extern reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest #127572

Mishura4 · 2025-02-18T06:44:16Z

// test.hpp

#include <vector>
#include <string>

extern const std::vector<std::string>& vec_ref;

void init();

// test.cpp
#include "test.hpp"

namespace
{

std::vector<std::string> impl;

}

const std::vector<std::string>& vec_ref = impl;

void init() {
    std::vector<std::string> vec;

    vec.push_back("hello");
    vec.push_back("world!");

    impl = std::move(vec);
}

// main.cpp
#include "test.hpp"

#include <iostream>

int main()
{
    init();
    for (auto& str : vec_ref)
    {
        std::cout << str << std::endl;
    }
}

Compile with clang-cl test.cpp main.cpp /std:c++latest. For some reason either vec_ref or impl seems to become corrupted and the for loop seems to read garbage data. In the project I initially encountered this, the program crashed with an access violation in std::vector::begin().

Observations:

The issue seems to be with /std:c++latest, the same code works without an issue on 20.1.0-rc2 with /std:c++20
The same code works without an issue on 19.1.7 even with /std:c++latest.

clang-cl was compiled with:

set CXX=clang-cl
set CC=clang-cl
set VECTORIZE="-march=native -mtune=native"

cmake llvm/ -B build ^
  -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld;lldb" ^
  -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx" ^
  -DLLVM_TARGETS_TO_BUILD=Native ^
  -DLLVM_PARALLEL_COMPILE_JOBS=30 ^
  -DLLVM_PARALLEL_LINK_JOBS=3 ^
  -DLLVM_ENABLE_LLD=on ^
  -DCLANG_DEFAULT_LINKER=lld ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCLANG_ENABLE_BOOTSTRAP=On ^
  -DLLVM_HOST_TRIPLE=x86_64-pc-windows-msvc ^
  -DLLVM_ENABLE_LTO=Thin ^
  -DLLVM_ENABLE_EH=ON ^
  -DLLVM_ENABLE_RTTI=ON ^
  -DLLVM_ENABLE_LIBXML2=ON ^
  -DCMAKE_CXX_STANDARD=20 ^
  -DBOOTSTRAP_CMAKE_CXX_FLAGS=%VECTORIZE% ^
  -DBOOTSTRAP_CMAKE_C_FLAGS=%VECTORIZE% ^
  -DBOOTSTRAP_CMAKE_EXE_LINKER_FLAGS=%VECTORIZE% ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_EH=ON ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_RTTI=ON ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_LIBXML2=ON ^
  -DCMAKE_MT=mt.exe ^
  -G Ninja

ninja -C build

(Issue also happens with -fuse-ld=link)

The text was updated successfully, but these errors were encountered:

dtcxzyw · 2025-02-18T06:49:14Z

It may be duplicate of #127475

llvmbot · 2025-02-18T06:49:47Z

@llvm/issue-subscribers-clang-codegen

Author: Miuna (Mishura4)

```c++ // test.hpp

#include <vector>
#include <string>

extern const std::vector<std::string>& vec_ref;

void init();


```c++
// test.cpp
#include "test.hpp"

namespace
{

std::vector&lt;std::string&gt; impl;

}

const std::vector&lt;std::string&gt;&amp; vec_ref = impl;

void init() {
    std::vector&lt;std::string&gt; vec;

    vec.push_back("hello");
    vec.push_back("world!");

    impl = std::move(vec);
}

// main.cpp
#include "test.hpp"

#include &lt;iostream&gt;

int main()
{
    init();
    for (auto&amp; str : vec_ref)
    {
        std::cout &lt;&lt; str &lt;&lt; std::endl;
    }
}

Compile with clang-cl test.cpp main.cpp /std:c++latest. For some reason either vec_ref or impl seems to become corrupted and the for loop seems to read garbage data. In the project I initially encountered this, the program crashed with an access violation in std::vector::begin().

Observations:

The issue seems to be with /std:c++latest, the same code works without an issue on 20.1.0-rc2 with /std:c++20
The same code works without an issue on 19.1.7 even with /std:c++latest.

clang-cl was compiled with:

set CXX=clang-cl
set CC=clang-cl
set VECTORIZE="-march=native -mtune=native"

cmake llvm/ -B build ^
  -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld;lldb" ^
  -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx" ^
  -DLLVM_TARGETS_TO_BUILD=Native ^
  -DLLVM_PARALLEL_COMPILE_JOBS=30 ^
  -DLLVM_PARALLEL_LINK_JOBS=3 ^
  -DLLVM_ENABLE_LLD=on ^
  -DCLANG_DEFAULT_LINKER=lld ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCLANG_ENABLE_BOOTSTRAP=On ^
  -DLLVM_HOST_TRIPLE=x86_64-pc-windows-msvc ^
  -DLLVM_ENABLE_LTO=Thin ^
  -DLLVM_ENABLE_EH=ON ^
  -DLLVM_ENABLE_RTTI=ON ^
  -DLLVM_ENABLE_LIBXML2=ON ^
  -DCMAKE_CXX_STANDARD=20 ^
  -DBOOTSTRAP_CMAKE_CXX_FLAGS=%VECTORIZE% ^
  -DBOOTSTRAP_CMAKE_C_FLAGS=%VECTORIZE% ^
  -DBOOTSTRAP_CMAKE_EXE_LINKER_FLAGS=%VECTORIZE% ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_EH=ON ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_RTTI=ON ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_LIBXML2=ON ^
  -DCMAKE_MT=mt.exe ^
  -G Ninja

ninja -C build

(Issue also happens with -fuse-ld=link)

Mishura4 · 2025-02-18T06:49:59Z

Yep, looks very similar

Mishura4 · 2025-03-23T02:52:14Z

Fixed in 9010db1

llvmbot · 2025-03-23T02:55:11Z

@llvm/issue-subscribers-clang-frontend

Author: Miuna (Mishura4)

```c++ // test.hpp

#include <vector>
#include <string>

extern const std::vector<std::string>& vec_ref;

void init();


```c++
// test.cpp
#include "test.hpp"

namespace
{

std::vector&lt;std::string&gt; impl;

}

const std::vector&lt;std::string&gt;&amp; vec_ref = impl;

void init() {
    std::vector&lt;std::string&gt; vec;

    vec.push_back("hello");
    vec.push_back("world!");

    impl = std::move(vec);
}

// main.cpp
#include "test.hpp"

#include &lt;iostream&gt;

int main()
{
    init();
    for (auto&amp; str : vec_ref)
    {
        std::cout &lt;&lt; str &lt;&lt; std::endl;
    }
}

Compile with clang-cl test.cpp main.cpp /std:c++latest. For some reason either vec_ref or impl seems to become corrupted and the for loop seems to read garbage data. In the project I initially encountered this, the program crashed with an access violation in std::vector::begin().

Observations:

The issue seems to be with /std:c++latest, the same code works without an issue on 20.1.0-rc2 with /std:c++20
The same code works without an issue on 19.1.7 even with /std:c++latest.

clang-cl was compiled with:

set CXX=clang-cl
set CC=clang-cl
set VECTORIZE="-march=native -mtune=native"

cmake llvm/ -B build ^
  -DLLVM_ENABLE_PROJECTS="clang;clang-tools-extra;lld;lldb" ^
  -DLLVM_ENABLE_RUNTIMES="compiler-rt;libcxx" ^
  -DLLVM_TARGETS_TO_BUILD=Native ^
  -DLLVM_PARALLEL_COMPILE_JOBS=30 ^
  -DLLVM_PARALLEL_LINK_JOBS=3 ^
  -DLLVM_ENABLE_LLD=on ^
  -DCLANG_DEFAULT_LINKER=lld ^
  -DCMAKE_BUILD_TYPE=Release ^
  -DCLANG_ENABLE_BOOTSTRAP=On ^
  -DLLVM_HOST_TRIPLE=x86_64-pc-windows-msvc ^
  -DLLVM_ENABLE_LTO=Thin ^
  -DLLVM_ENABLE_EH=ON ^
  -DLLVM_ENABLE_RTTI=ON ^
  -DLLVM_ENABLE_LIBXML2=ON ^
  -DCMAKE_CXX_STANDARD=20 ^
  -DBOOTSTRAP_CMAKE_CXX_FLAGS=%VECTORIZE% ^
  -DBOOTSTRAP_CMAKE_C_FLAGS=%VECTORIZE% ^
  -DBOOTSTRAP_CMAKE_EXE_LINKER_FLAGS=%VECTORIZE% ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_EH=ON ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_RTTI=ON ^
  -DRUNTIMES_x86_64-pc-windows-msvc_LLVM_ENABLE_LIBXML2=ON ^
  -DCMAKE_MT=mt.exe ^
  -G Ninja

ninja -C build

(Issue also happens with -fuse-ld=link)

llvmbot added the new issue label Feb 18, 2025

dtcxzyw added clang:codegen miscompilation and removed new issue labels Feb 18, 2025

Mishura4 changed the title ~~[clang-cl] access violation at runtime with clang-cl 20.1.0-rc2 using /std:c++latest~~ [clang-cl] access violation with a global reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest Feb 18, 2025

Mishura4 changed the title ~~[clang-cl] access violation with a global reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest~~ [clang-cl] access violation with an extern reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest Feb 18, 2025

Mishura4 closed this as completed Mar 23, 2025

EugeneZelenko added the clang:frontend label Mar 23, 2025

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[clang-cl] access violation with an extern reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest #127572

[clang-cl] access violation with an extern reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest #127572

Mishura4 commented Feb 18, 2025 •

edited

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dtcxzyw commented Feb 18, 2025

llvmbot commented Feb 18, 2025

Mishura4 commented Feb 18, 2025

Mishura4 commented Mar 23, 2025 •

edited

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llvmbot commented Mar 23, 2025

[clang-cl] access violation with an extern reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest #127572

[clang-cl] access violation with an extern reference at runtime with clang-cl 20.1.0-rc2 using /std:c++latest #127572

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Mishura4 commented Feb 18, 2025 • edited Loading

dtcxzyw commented Feb 18, 2025

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Mishura4 commented Feb 18, 2025

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Mishura4 commented Feb 18, 2025 •

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Mishura4 commented Mar 23, 2025 •

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