How do I use an exisiting function pass from my LLVM - pass?

Question

I have been using LLVM and I was confused how to use a different already present pass from my own pass ? Precisely my program needs Dominance Frontier Calculation for any given instruction. LLVM already has the Dominance function Class that is implemented as a function pass. How can i invoke it/make use of it in my Module Pass ?

Have you checked the docs? Because the last time I checked, the answer was there: llvm.org/docs/WritingAnLLVMPass.html — user784668
– user784668, Commented Feb 17, 2012 at 18:58
Add AU.addRequired<DominanceFrontier>(); to your pass getAnalysisUsage(AnalysisUsage &AU) method. — osgx
– osgx, Commented Feb 17, 2012 at 18:59
The documentation is really obscure and I had real problems deciphering it. An example would have helped. — Sharad
– Sharad, Commented Feb 17, 2012 at 19:09
What is your version of LLVM? What kind of information do you want to get? — osgx
– osgx, Commented Feb 17, 2012 at 19:12

Sharad · Accepted Answer · 2012-04-09 02:09:09Z

4

WARNING: I have no real experience and answer may be incorrect or outdated. (it is based largely on outdated LLVM sources: version 1.3.)

Add an include:

#include "llvm/Analysis/DominanceFrontier.h"

If your pass if Function Pass, add to your class the method (if it is not implemented):

virtual void getAnalysisUsage(AnalysisUsage &AU) const { }

And put this into it:

 AU.addRequired<DominanceFrontier>();

Then, in your class runOnFunction method:

 DominanceFrontier *DF = &getAnalysis<DominanceFrontier>();

After this you can use:

    BasicBlock *BB = /* some BB */;
    DominanceFrontier::iterator DFI = DF->find(BB);

edited Apr 9, 2012 at 2:09

Sharad

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answered Feb 17, 2012 at 19:07

osgx

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