llvm dev - Jun 2015 - [LLVMdev] Moving instructions from one basic block to another

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

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

On 6/26/2015 11:08 AM, Frank Winter wrote:
> 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
>
>
>
>
>
>
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