In llvm, how can I delete a whole branch elegantly?

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#1

Hi,

I am trying to prune some uninteresting llvm ir branches, corresponding to the if-else condition in the source code. And here is the procedures:

  1. Get the BasicBlock containing the BranchInst which has 2 successors(in order to keep consistent with the source code I am using the llvm ir without any optimizations, so SelectInst/SwitchInst/PHINode is absent), one of which should be pruned; let’s name these 2 branches bb1 and bb2 and bb2 is to be pruned.

  2. Find their nearest common post dominator, bb_join

  3. Create a new branInst bb_new whose successors are bb1 and bb_join; replace the original BranchInst with bb_new

  4. For bb2, dropAllReferences && eraseFromParent

However since bb2 also has several successors(before bb_join), which are not pruned together with bb2. Is there any existing API to remove them as well?

Also, in Step 4, could I just call bb2->eraseFromParent() without dropping any references? I am a bit confused with the function dropAllReferences.

Thanks,

Hongxu Chen

#2

Sorry for the pollute, I later found that DeleteDeadBlock(BasicBlock *B) inside BasicBlockUtils.h might be helpful since it just removes those blocks without any predecessors. Now I am using Function::iterator with this function to remove those dangling basicblock nodes. However I still have no idea whether this can prune ALL the suspicious blocks, in theory(still the presiquite, no optimization and only for if-else like branches). And is there a better way?

Thanks,

Hongxu Chen