METALOC: Robustifying Debug Location Updates in LLVM

For artifact evaluation, please check EVALUATION.md.

Main Components

1. AST-level pass instrumentation tool (Rust, under src/)
2. Build-in LLVM library (C++, under library/)

Prerequisite

• rust compilation environment (cargo, rustc...)
• Provide your own LLVM project directory (modify the configurations in config.json). "llvm" gives the path to llvm root; "opt" specifies the path to opt binary (required for running instrumented optimizations).

{
    "llvm": "your/path/to/llvm-project/llvm",
    "opt": "your/opt/binary",
}

Compile LLVM

If the LLVM has already been compiled, please skip.

1. Clone the LLVM repo and install build tools. For saving time, you can add the flag --depth=1 when cloning.

$ git clone https://github.com/llvm/llvm-project.git
$ sudo apt install ninja-build cmake

2. Initialize the build directory.

$ cd llvm-project
$ cmake -S llvm -B ../build-llvm -G Ninja \
	-DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=On \
	-DCMAKE_INSTALL_PREFIX=../llvm

3. Build the opt

$ cd ../build-llvm && ninja opt

How to Use

STEP 1: Copy the Library into LLVM

This step copies the implemented library to the directory of LLVM's include files, i.e., llvm/include/llvm/Transforms/Utils/.

$ python3 script/metaloc.py setup

STEP 2: Instrument the Target Optimization Pass

This step instruments a given LLVM optimization pass.

$ python3 script/metaloc.py instrument path/to/llvm/lib/Transforms/Scalar/TailRecursionElimination.cpp

After this step, the LLVM project (especially opt) should be rebuild.

$ ninja opt

STEP 3: Run the Instrumented Optimization Pass

One can simply use opt to run the instrumented optimization pass with a specified test case.

$ opt -S -passes=tailcallelim dropping_debugloc_acc_rec_inst_rnew.ll --disable-output

Or use the script to analyze the instrumented pass with a bunch of test cases.

$ python3 script/metaloc.py analyze path/to/llvm/test/Transforms/TailCallElim/

In the output, potential debug location update errors denoted by FAIL are printed along with the constructed proper updates.