CODEWITHSUNDEEP
optimizationllvm
harry
harry

Reputation: 1095

LLVM Immutable Pass

I'm going through the LLVM Pass classes and didn't quite understand the ImmutablePass. Can someone give an example of how is it helpful and when should we use it?

Upvotes: 0

Views: 217

Answers (1)

CPPCPPCPPCPPCPPCPPCPPCPPCPPCPP
CPPCPPCPPCPPCPPCPPCPPCPPCPPCPP

Reputation: 1025

You can check the examples in LLVM itself: https://github.com/llvm/llvm-project/search?q=%22public+ImmutablePass%22. There are only 2 pages in the search.

By looking of the code itself, you can see that it is not doing so much lol: https://github.com/llvm/llvm-project/blob/86341247c4a2ffa4328945b03e7a05b1c51c3889/llvm/include/llvm/Pass.h#L269.

As I see, if you consider not to use runOnModule, runOnFunction and affect LLVM module somehow, you can use ImmutablePass.

Soooooo, everything these passes additionally have:

  • initializePass() which is settable by user
  • bool runOnModule(Module &) override { return false; }

Personally, I remember that LLVM runs some immutable passes before meaningful passes, due if it won't be done, these other passes will segfault due the lack of some information...

Upvotes: 1

Related Questions