SSIfy

Overview

SSIfy is a parameterized tool for constructing program representations suitable for program static analyses. Given an input program, it can be converted to forms such as Extended Static Single Assignment, Static Single Use, etc.

The main motivation is to offer an all-in-one solution, which is capable of producing program representations that combine properties of different forms. That is, one can transform a program to a representation which is, loosely speaking, e-SSA and SSU at the same time.

Current version: 2.0.

Compatibility

SSIfy works on LLVM 3.7. Along with installing SSIfy, it's necessary to deploy a modified version of LLVM's Dominators.h, also provided here.

Modes of operation

SSIfy has two modes of operation: upwards and downwards. These should be selected according to the purpose of the analysis that will follow the transformation. That is, if the analysis flows information down (e.g. tainted flow analysis, range analysis), you should set the downwards mode on. Likewise, if the analysis flows information up (e.g. class inference), you should set the upwards mode on.

In conjunction with the flow direction option, you can also specify where the live range splitting should occur. The two options are (i) in the exit of conditional branches and (ii) after uses of values.

Implementation

This is done as a compiler pass that works on LLVM 3.7, written in C++.

Requirements

In order to use SSIfy on LLVM bitcode programs, one has to run it through the following passes first:

1. mem2reg;

2. break-crit-edges;

Also, for cosmetic reasons, it is recommended to run instnamer pass after all passes that create new variables.

Installing

1. Build LLVM: http://llvm.org/docs/GettingStarted.html
2. Put Dominators.h inside llvm/include/llvm/IR/.
3. Put the SSIfy folder inside llvm/lib/Transforms/.
4. Build SSIfy by running make in the root of the build dir.

How to run

After building LLVM and SSIfy, you can try it with the command:

$ opt -mem2reg -break-crit-edges [... -instnamer] -load /path/to/SSIfy.so -ssify [-v] FLAGS Input.bc -o Output.bc

-v: verbose mode

FLAGS determine how SSIfy will split live ranges in the program:

1. -essa: Extended Static Single Assignment
2. -ssu: Static Single Use
3. -essa-up: upwards e-SSA
4. -ssu-up upwards SSU

Further

If you have any questions or suggestions, I'd be happy to address them. Reach out on victorsc at dcc.ufmg.br