[LLVMdev] Cloning BasicBlock

[Sandra Johnson]

  Hello Andrew ,
  Yes , I have missed the phi node since my paths merge together. I'll try this out.
  I am implementing a timer based profiling scheme and hope your code will be useful 
  for me. Please send me a copy of your code. 
   
  Thanks
  Sandra


Andrew Lenharth <andrewl at lenharth.org> wrote:  On Tue, 2005-11-22 at 09:12 -0800, Sandra Johnson wrote:
> Hi ,
> I am trying to clone a BasicBlock. I want both to co-exist and I have
> introduced
> a conditional branch to the original or the cloned BB. 

I have a pass I haven't commited that does just this. Well, it does so
to implement Arnold and Ryder style profiling. I can send you a copy of
that if you want (I hope to commit it soon once it is cleaned up some).
Your best bet is to run reg2mem, which removes most live values by
placing them in memory. the only live values that remain after that
pass are the allocas for the old registers and values from loads in the
predecessors of phi nodes to those phi nodes. This makes it much easier
to maintain SSA form (as there is only one type of simple live value you
have to worry about). It is also possible to remove the phi nodes
completely with a bit more transform, but that wasn't desirable in my
case, so I didn't, but you could easily extend the pass to do so.

(just for reference, my code clones all BB in a function and the CFG,
then takes backedges and interconnects the backedges of the original and
cloned versions, adding conditional branches at those join points.)

Andrew Lenharth

> I tried mapping the original instruction and the clone as below :
> Instruction *NewInst = II->clone();
> if (II->hasName())
> NewInst->setName(II->getName());
> NewBB->getInstList().push_back(NewInst);
> ValueMap[II] = NewInst; 
> what I got from this is ,
> --> eventhough I have set the same name , a new name is set
> for the clone.
> original :
> %CS1 = call fastcc int %add( int %tmp.5, int %
> tmp.6 ) ; [#uses=1]
> clone :
> %CS11 = call fastcc int %add( int %tmp.5, int %
> tmp.6 ) ; [#uses=1]
> --> the verifier gives the following error
> Instruction does not dominate all uses!
> &n! bsp; for the original instruction.
> Is it possible to have the instructions in the clone to have the same
> name 
> as the original BB ?
> Is it possible to make the uses of the original instruction to be the 
> uses of the cloned instruction at the same time ? 
> What makes the above error ?
> Is it because of SSA ? 
> 
> 
> Thanks in advance for any help,
> Sandra
> 
> 
> 
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