[LLVMdev] How to insert a basic block in an edge

[Chayan Sarkar]

Hi All,

Still I could not figure out how to use Pass* while calling
SplitEdge() function. Can anyone provide me some example?

Regards,
Chayan

On Sun, Jul 18, 2010 at 11:49 PM, Nick Lewycky <nicholas at mxc.ca> wrote:
> Chayan Sarkar wrote:
>>
>> 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.
>
> The only reason it needs a non-NULL Pass* is to call llvm::SplitBlock which
> uses P->getAnalysisIfAvailable unconditionally. Feel free to wrap those
> calls in 'if (P) { ... }' and send us a patch.
>
> Of course, the obvious question is why aren't you doing your transforms
> inside of a Pass?
>
> Nick
>
>> 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
>>>
>>
>
>