TargetLibraryInfoAliasAnalysis - A pass for LLVM opt

Introduction

This is a pass using LLVM opt.

Features

• Out-of-source builds thanks to cmake.
• In-tree LLVM builds.

Requirements

• cmake 3.2.0 or later
• C++ compilers:
  • LLVM
    tested with:
    • 3.7.x
    • 7.0.0
  • GCC
    tested with:
    • 5.4.1
  • googletest
    tested with:
    • 1.8.0

External dependencies

Mandatory

• cmake-utils
  Used for supporting the cmake-based build system. Using git clone --recursive should take care of everything.
• sanitizers-cmake Used to provide support for sanitizers. Although the subproject is required for successful configuration, its use is optional.

Optional

None.

How to build

1. git clone --recursive this repo.
2. Create a directory for an out-of-source build and cd into it.
3. Run cmake and cmake --build . with that appropriate options. For examples on the various options have a look at the build scripts (provided for convenience) located in the utils/scripts/build subdirectory.

• compiler selection is catered by the exports_local_* scripts using the CC and CXX variables for my current machine, so adjust appropriately for your setup.
• export one of the exports_deps_* scripts, depending on the kind of setup you are interested in.

4. Optionally, you can install the pass by

   cmake -DCMAKE_INSTALL_PREFIX=[path-to-install] -P cmake_install.cmake

   Omitting CMAKE_INSTALL_PREFIX will use the ../install/ directory relative to the build directory.

5. lit-based tests can be run with cmake --build . --target check

6. googletest-based unit tests can be run with ./run_unit_tests.sh (see the script for details).

How to execute

Using opt

opt -load [path to plugin]/libLLVMTargetLibraryInfoAliasAnalysisPass.so -tli-aa foo.bc -o foo.out.bc

Using clang

clang -Xclang -load -Xclang [path to plugin]/libLLVMTargetLibraryInfoAliasAnalysisPass.so foo.c -o foo

Notes

Customizing

A first step towards customization is to search for the pattern [Ss]keleton] and replace as with the desired name. A general good approach is to prefix everything with the name of the pass, especially in languages that do not offer some sort of namespace capability like cmake.

Another customization that needs to be take care of in the case of creating a new project based on this template is the use of cmake-utils. There are 3 options:

• Just copy the files and include them in the new repository.
• Use it as a submodule using the initial URL address.
• Use it as a submodule using a fork of the initial URL address. This allows you to keep the repo separately and have full control on updates and other desired enhancements.

Clarifications on building

The shared object containing the pass is dynamically loaded by opt. This poses a restriction on its build dependency upon opt and its transient dependency to the C++ library it is linked against. So, it is recommended to perform readelf -d $(which opt) and note which implementation of the C++ library it uses (libc++ or libstdc++). Then, you can influence which C++ library your pass uses with the CMAKE_CXX_FLAGS and the -stdlib flag for LLVM.

The main problem stems from the binary incompatibility (ABI) between the two implementations, although they are API compatible since they adhere to the ISO standard. For this reason, libc++ uses the inlined namespace std::__1, which will show up in the errors when you have your pass built against libstdc++ and try to load it using an opt built against libc++.

When LLVM is build with BUILD_SHARED_LIBS=OFF, opt cannot load dynamically any pass built as a shared object, complaining about multiply defined symbols, since it contains everything in its executable. The only workaround is to build your pass in the LLVM tree (resulting in a static archive, also included in the opt executable).

Miscellaneous

When the build script uses LLVM cmake utility functions the lib shared library prefix is omitted.

TODO

• Add travis-ci support.