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

Hongxu Chen leftcopy.chx at gmail.com
Wed Sep 18 02:45:02 PDT 2013


   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

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

Hongxu Chen
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