RiscInside / SimpleLLVMPass

SImple LLVM pass for LLVM11

Simple LLVM pass

This repository contains a simple example of a fully functional LLVM pass.

CountPass.cpp file implements a simple LLVM pass that calculates number of functions, basic blocks, and instructions in each basic block. This pass also produces a histogram of basic blocks by instruction count using gnuplot tool.

Dependencies

This project requires llvm-11, make, cmake, and gnuplot to be installed.

Building

CMake build system is used to build an LLVM plugin with the pass. Makefile wrapper is provided for convinience.

Run make build to build the plugin.

Run make to test the plugin on the program.c file:

int main(int argc, char **argv) {
  if (argc != 2) {
    printf("The program expects one argument\n");
    return 1;
  }

  if (argv[1][0] == 'A')
    printf("A\n");
  else if (argv[1][0] == 'B')
    printf("B\n");
  else
    printf("C\n");

  return 0;
}

By default, Makefile uses clang and opt commands for emiiting LLVM IR and running the pass. To use clang-11 and opt-11 instead, set CLANG and OPT variables to clang-11 and opt-11 respectfully.

make CLANG=clang-11 OPT=opt-11

Acknowledgements

This blog helped me to figure out how to draw histograms in gnuplot.

This page helped me with writing skeleton code for this LLVM pass.

I used CMakeLists.txt from this GitHub repository with some minor changes.