https://github.com/dtcxzyw/conservative-clang

An early LLVM pass which removes most of UB-implying information
https://github.com/dtcxzyw/conservative-clang

clang compiler llvm llvm-pass optimzation undefined-behavior

Last synced: 3 days ago
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An early LLVM pass which removes most of UB-implying information

• Host: GitHub
• URL: https://github.com/dtcxzyw/conservative-clang
• Owner: dtcxzyw
• License: apache-2.0
• Created: 2024-08-04T22:39:47.000Z (6 months ago)
• Default Branch: main
• Last Pushed: 2025-01-20T12:41:58.000Z (4 days ago)
• Last Synced: 2025-01-20T13:48:28.479Z (4 days ago)
• Topics: clang, compiler, llvm, llvm-pass, optimzation, undefined-behavior
• Language: C++
• Homepage:
• Size: 18.6 KB
• Stars: 8
• Watchers: 2
• Forks: 2
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Conservative-Clang

Conservative-Clang: An early LLVM pass which removes most of UB-implying information.

If you are fighting with C/C++ undefined behavior (or clang miscompilation bugs), please try this tool :)

Before using the pass, please try with the following compilation flags in [clang-flags.txt](./clang-flags.txt):

```

-fwrapv -fno-check-new -fno-delete-null-pointer-checks -fno-strict-aliasing -fno-strict-enums -fno-strict-float-cast-overflow -fno-strict-return -fno-strict-vtable-pointers -fno-struct-path-tbaa -fno-pointer-tbaa -fno-assume-nothrow-exception-dtor -fno-assume-sane-operator-new -fno-assume-unique-vtables -fno-assumptions -fno-finite-loops -fno-common -mno-global-merge -fno-merge-all-constants -fno-strict-overflow

```

If this "magical formula" does not work, please try the LLVM pass.

This work is inspired by Daniel J. Bernstein's [blog](https://blog.cr.yp.to/20240803-clang.html). I hope this work can unblock your project at the prototype stage.

## Getting Started

### Installation

```bash

sudo apt install llvm-20-dev # Depends on your clang version

git clone https://github.com/dtcxzyw/conservative-clang.git

cd conservative-clang

mkdir -p build && cd build

cmake .. -DCMAKE_BUILD_TYPE=Release

cmake --build . -j

```

### Usage

```bash

export CFLAGS=-fpass-plugin=/build/cclang.so

export CXXFLAGS=-fpass-plugin=/build/cclang.so

# Configure & build your project

```

If you are using CMake, please pass `-DCMAKE_C_FLAGS=-fpass-plugin=/build/cclang.so -DCMAKE_CXX_FLAGS=-fpass-plugin=/build/cclang.so` to CMake.

## Performance

I did some performance evaluation on llvm test-suite. This pass can result in ~10% performance degradation on average.

## License

This project is licensed under the Apache License 2.0. Please see the [LICENSE](./LICENSE) for details.