llvm dev - Jul 2010 - [LLVMdev] How to insert a basic block in an edge

Hi all,

Suppose in a CFG bb1 has two succesor bb3 and bb4, and bb3 has two
predecessor bb1 and bb2. Now how can I insert a basic block between
bb1 and bb3 that at the edge bb1-->bb3 .

In general how can I insert a basic block on an edge?

Regards,
Chayan

Chayan Sarkar wrote:
> Hi all,
>
> Suppose in a CFG bb1 has two succesor bb3 and bb4, and bb3 has two
> predecessor bb1 and bb2. Now how can I insert a basic block between
> bb1 and bb3 that at the edge bb1-->bb3 .
>
> In general how can I insert a basic block on an edge?
Use llvm::SplitEdge in Transforms/Utils/BasicBlockUtils.h.

The technique is to create a new bb with a single branch to bb3, then 
modify bb1's use of bb3 to point to 'new bb' instead, then fix up
any
phi nodes in bb3 by replacing uses of bb1 with 'new bb'.

Nick

Hi,

I have tried to use SplitEdge function, but failed. Actually the third
parameter is a variable of type Pass and it need to be non-null. But I
could not figure out how to use it. Please help me out.

Regards,
Chayan

On Sat, Jul 17, 2010 at 10:16 PM, Nick Lewycky <nicholas at mxc.ca>
wrote:
> Chayan Sarkar wrote:
>>
>> Hi all,
>>
>> Suppose in a CFG bb1 has two succesor bb3 and bb4, and bb3 has two
>> predecessor bb1 and bb2. Now how can I insert a basic block between
>> bb1 and bb3 that at the edge bb1-->bb3 .
>>
>> In general how can I insert a basic block on an edge?
>
> Use llvm::SplitEdge in Transforms/Utils/BasicBlockUtils.h.
>
> The technique is to create a new bb with a single branch to bb3, then
modify
> bb1's use of bb3 to point to 'new bb' instead, then fix up any
phi nodes in
> bb3 by replacing uses of bb1 with 'new bb'.
>
> Nick
>