Moving instructions from one basic block to another

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1

Say, you have basic blocks BB_source and BB_dest, where BB_source contains many instructions and some of them you'd like to move to BB_dest where the builder's insertion point currently points to. The instructions to move are stored in a SetVector<Value*> in no particular order. Thus, moving the instructions (removeFromParent and Builder->insert) while iterating over the set vector causes problems a la 'value does not dominate all uses'. However, iterating over BB_source and checking for presence of the processed instruction in the set vector and moving it to BB_dest seems to invalidate the iterator. Here's the code I am trying:

   for (BasicBlock::iterator inst = BB_source->begin() ;
        inst != BB_source->end() ;
        ++inst ) {
     if (Instruction *Inst = dyn_cast<Instruction>(inst)) {
       if (set_vector->instructions.count(Inst)) {
        Inst->removeFromParent();
        Builder->Insert(Inst);
       }
     }
   }

That doesn't work. I was already wondering if I am on the right path since the simplified version doesn't compile:

   for (BasicBlock::iterator inst = BB_source->begin() ;
        inst != BB_source->end() ;
        ++inst ) {
       if (set_vector->instructions.count(inst)) {
        inst->removeFromParent();
        Builder->Insert(inst);
     }
   }

How would You do that?

Thanks,
Frank

2

You can use BB->getInstList().splice(...) to move instructions across basic block boundaries. Look in include/llvm/ADT/ilist.h for the declaration of splice.

-Krzysztof