/cs6120-llvm-pass

Primary LanguageC++MIT LicenseMIT

llvm-pass-skeleton (Modified by Griffin Berlstein for CS6120)

A completely mostly useless LLVM pass. Based on the tutorial by Adrian Sampson (@sampsyo).

Build:

$ cd llvm-pass-skeleton
$ mkdir build
$ cd build
$ cmake ..
$ make
$ cd ..

Run:

$ clang -Xclang -load -Xclang build/skeleton/libSkeletonPass.* something.c helpers.c

The pass

This modified pass inserts calls to simple functions that print out messages when certain reducible operations are executed. The flagged operations are:

  1. a + 0 - Could be replaced by a
  2. a - 0 - Could be replaced by a
  3. a * 0 - Could be replaced by 0
  4. a / 1 (int div) - Could be replaced by a
  5. a * 1 - Could be replaced by a
  6. a & 0 - Could be replaced by 0
  7. a ^ 0 - Could be replaced by a
  8. a | -1 - Could be replaced by -1
  9. a ^ a - Could be replaced by 0
  10. a | a - Could be replaced by a
  11. a & a - Could be replaced by a

The pass doesn't remove any of these actions, it just places a call to the printing function after the computation. This will in fact make the program execute slower which we can pretend is a means of discouraging such behavior.