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

[Chayan Sarkar]

Hi,

I could not figure out, how to declare a Pass*. Can anyone give me an
example, how to use SplitEdge() function ?

Please help me out.

Regards,
Chayan

On Tue, Jul 20, 2010 at 10:12 AM, Chayan Sarkar <chayan.ju at gmail.com> wrote:
> 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
>>>>
>>>
>>
>>
>