[LLVMdev] Regarding BasicBlock Cloning

[John Criswell]

On 4/16/11 7:01 PM, tarun agrawal wrote:
> The clone llvm:CloneBasicBlock copies the phi function in the 
> replicated basic block from the original basic block.

After you clone the basic block, you can probably replace the phi 
instruction with another value of your choice.  If you're adding 
variables, you'll probably want to create them as allocas and use loads 
and stores to access them.  In such as case, you'd replace the phi in 
the new BasicBlock with a load of your new variable.

Once all your basic blocks are in place and all the terminator 
instructions are modified so that your control-flow graph is the way you 
want it to be, you can run mem2reg to change your alloca variables into 
real SSA variables with phi-nodes in your new basic blocks.

-- John T.


> I don't want the copy of phi in relplicated block. For now I am 
> creating .bc file with -O0 option so that it doesn't generate phi 
> function in first place. Is this a good approach or there are some 
> other function available for it.
>
> Tarun
>
> On Sun, Apr 17, 2011 at 5:22 AM, Eli Friedman <eli.friedman at gmail.com 
> <mailto:eli.friedman at gmail.com>> wrote:
>
>     On Sat, Apr 16, 2011 at 4:32 PM, tarun agrawal
>     <tarun at cse.iitb.ac.in <mailto:tarun at cse.iitb.ac.in>> wrote:
>     > Hi,
>     >
>     > I am writing a pass for constant propagation using graph
>     restructuring (
>     > code duplication). I am facing following difficulties..
>     >
>     > 1) I need to replicate the basic block but without phi function
>     in the
>     > replicated block. How can I do this.
>     >
>     > 2) I need to insert that basic block after and before some
>     particular basic
>     > block.
>
>     You probably want to use llvm::CloneBasicBlock from
>     Transforms/Utils/Cloning.h to get a cloned version of a block.
>     BasicBlock::splitBasicBlock might be useful as well.
>
>     -Eli
>
>
>
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